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Maño accent starts SOMONPARTY 2010

A little over a month to the third edition of SOMONPARTY, Hall of users of new technologies, this morning had held a press conference in which we presented the new website for this issue and Journals and DJ competitions.

A failure to close the whole program acts, which this year includes professional workshops on ICT, developments in digital entertainment and events such as Wine & Blogs, repeat the contests were so successful in its previous edition and for those already open enrollment periods. Contest

SOMONPARTY 2010
Journals Open to any person who has his own blog, the II Journals SOMONPARTY maintains the intention of recognizing the efforts of those who have chosen this new form of communication, free and altruistic, sharing their knowledge and concerns around the world.

bases, categories and awards are similar to the previous edition. You can consult and register at the following link:
http://www.somonparty.com/index.php?somonparty=05_b

Updated
registration deadline extended to Thursday, 5 August.

SOMONPARTY DJ Competition 2010
Sound Machine Music and technology come together at this festival that celebrates its second edition, after great success in the first. During this festival will be held DJ Contest final and one of the main DJ on the national scene, juror DJ Contest will close the festival with a professional session.

Here also the link to the bases and form Registration:
http://www.somonparty.com/index.php?somonparty=06_b

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Photodiode amplifier, current to voltage converter amplifier with feedback

A high-efficiency amplifier for photodiode is often indispensable. If one takes into account the current delivered by the photodiode is very small, to amplify the signal it receives is very useful.

Although you can use a large number of different operational amplifiers to perform this amplification was used in this case a LM308, because it has a great profit, is more immune to noise than other operational and its frequency response is better (must be taken into account that the gain of an op amp decreases with increasing frequency).

This circuit is designed to receive pulses of light. If we want this amplifier is used as light detector is to remove the capacitor C1 and the photodiode must be connected directly to the noninverting input (negative symbol-) operational amplifier (leg 2).

This circuit is very sensitive and works well as a receiver of light signals.

The amplifier is configured as an inverting amplifier. This means that the waveform of the output is opposite to the entrance (Deprecated 180 °). The amplifier gain can be adjusted with the potentiometer R2.

Another way to look at this circuit is as current converter (photodiode current) to voltage (output of operational amplifier). The output voltage is the product of the photodiode current by the resistance R1.

The capacitor C2 is used in the LM308 to improve its frequency response.

This circuit can also work with the operational amplifier 741C (cheaper), but the gain and frequency response is lower. In this case the capacitor C2 is not necessary

voltage Power may be between 6 and 15 volts.

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EES Section: 02

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Family

"Amplifier with feedback (CFB-current feedback) is an electronic circuit (usually presented as an integrated circuit) having two inputs and one output. The output is the difference of the two inputs multiplied by a factor (G) (gain):

The feedback amplifier is an alternative to voltage-feedback amplifiers, also called operational.

The feedback amplifier is an alternative the voltage-feedback amplifiers, also called operational.

negative feedback theory

Definition

general strategy of system design, whereby a magnitude proportional to the system output is subtracted from the reference input .

RN Advantages 

reduces system sensitivity to parameter variations. 

Increases bandwidth. 

reduces nonlinear distortion. 

Improves input impedances and output

feedback amplifier configuration

For amplifiers feedback voltage must increase and decrease Rin Rout, so that all the stress that comes from the input signal falls on the amp and all the tension of the output signal falls on the burden placed. In transresistance amplifiers feedback should decrease the lower Rhine and Ro, so that the entire current input signal passes through the amplifier and for the whole amplifier output voltage drop on the load placed. In the case of current feedback amplifiers to decrease and increase Rout Rin, so that the entire current input signal passes through the amplifier and for the entire output current passes through the load placed. And finally in the feedback transconductance amplifiers will increase and increase Ri Ro, for all the tension of the input signal falls on the amp, and that all the output current passes through the load placed.

The feedback increases or decreases Rin and Rout of the amplifiers is more like the ideal case.

feedback Types

feedback in voltage opposes any change in the input signal attempts to change the output voltage to reduce Rout (suitable for power amplifiers and transresistance)

feedback in current opposes the current change, making the output is a constant-current source to increase The Rout (suitable for current and transconductance amplifiers)

The Feedback Series. Is connected in series circuit with feedback amplifier. This increases the input resistance (suitable for amp. Voltage and transconductance).

The Parallel Feedback. Are connected in parallel circuit and the feedback amplifier. This reduces the input resistance (suitable for amp. Transrresistencia current and).

series voltage feedback to voltage amplifier.

current feedback amplifier in parallel to current.

Advantages

The main advantage of development using current feedback amplifiers with high speed is provided. Consequently, it has been shown to increase the speed has the advantage of improved sound. Also, the speed affects the speed in which it may correct the faults that they themselves produce.

The current feedback amplifiers (CFA) is a type of electronic amplifier whose negative input is sensitive to lacorriente, unlike normal amplifiers that they are to stress (VFA).

The CFA was invented about 1988. They are usually produced as integrated circuits with the same pin assignment that VFA, thus allowing the two types can be easily interchanged. In simple configurations, such as linear amplifiers, a CFA can be used in place of a VFA without modifying the circuit, but in other cases, such as integrators need a redesign. The classic configuration of the amplifier with four resistors will also work with a CFA, but the CMRR is very poor.

Mario Dominguez Zambrano EES

Section: 02

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LM124 operational amplifiers, LM224, LM324

Integrated circuits of this family of amplifier contains four independent operational amplifiers in the same package. High gain, internal compensation and the wide range of power supplies are the main features. Its low power consumption allows for use in battery powered equipment. Unlike other operational amplifiers require power supplies of ± 15V, these amplifiers can operate with simple supplies voltage of only 5V.

Features

 High gain at low frequencies: 100,000 times

 Bandwidth of 1MHz offset heat

 Wide supply voltage range: 3V - 32V, or ± 1.5V - ± 16V

 Low power consumption, only 700 uA

 voltage range equals input voltage Power

 minimum output voltage: 0v 

Maximum output voltage: positive voltage less than 5V

Operating temperature

 LM124 -55 ° C to +125 ° C

 LM224 -25 ° C to +85 ° C

 LM324 0 ° C to +70 ° C

Illustration of a package of amplificadoroperacional LM124 DIP14

Pin Distribution Amplifier

Mario Dominguez Zambrano

EES Section: 02

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Effect of the use of Schmitt trigger (B) instead of a comparator (A)

In electronics a Schmitt trigger Schmitt trigger is a special type of comparator circuit. It was invented by American Otto Herbert Schmitt.

Operation

A Schmitt trigger output changes state when the voltage at its input exceeds a certain level, the output does not change back when the low input voltage, but the level of tension for change is a different, lower than the first. This effect is called hysteresis. This is the main difference with a normal comparator, which is a simple operational amplifier without feedback, and that its output depends only on the largest input.

The uses Schmitt trigger hysteresis to prevent noise that could overlap with the original signal and cause false changes in status if the reference and input levels are similar.

For its implementation is often used an operational amplifier positive feedback. The reference levels can be controlled by adjusting the resistors R1 and R2:

For example, if the initial trigger is activated, the output is in high state at a voltage Vout = + Vs, and the two resistors form a voltage divider between the output and input. The tension between the two resistors (entry +) is V +, which is compared with the input voltage - which assume 0V (in this case, the absence of negative feedback in the operational, the tension between the two inputs need not be the same). To produce a transition to the output, V + must descend and reach at least to 0V. In this case the input voltage is
At this point the output voltage changes Vout =- Vs For an argument equivalent to the condition we get to go from-Vs to + Vs:

This causes the circuit to create a band centered at zero, with trigger levels ± (R1 / R2) VS. The input signal must come from that band to get to change the output voltage.

If R1 or R2 is zero is infinity (open circuit) the band has a width of zero and a comparator circuit will work as normal.

To indicate that a logic gate is the Schmitt trigger type is placed on the inside of the hysteresis symbol:

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EES Section: 02

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Schmitt Trigger Electronic amplifier analogue-digital converters

Electronic amplifier can mean thus a kind of electronic circuit or stage of this, as a modular computer that performs the same function, and that is usually part of HIFI equipment. Its function is to increase the intensity of current, voltage or power signal is applied to its input, yielding the increased signal at the output. To amplify the power necessary to obtain energy from external power supply. In this sense, the amplifier can be considered as a modulator output power

HIFI Class D amplifier circuit of 200W RMS into 4 Ohm speaker.

FEATURES

The amplifier can perform its function in a passive manner by varying the ratio between current and voltage at constant power (similar to a transformer), or actively, taking power from a power supply and increasing the power of the signal leaving the amplifier, usually keeping the shape of the signal, but giving it more widely.

The relationship between input and output of the amplifier can be expressed in terms frequency of the input signal, which is called transfer function, which indicates the gain of the same for each frequency. It is customary to keep an amplifier working within a certain range of frequencies over which behaves linearly, which means that its gain is constant for any amplitude to its input.

The main component of these amplifiers, called active element may be a vacuum tube or transistor. The vacuum tubes are often used even in some audio amplifiers designed specifically for the frequency response of these, preferred in some styles. Represent the base transistors electronics modern. They are designed with more complex circuits such as operational amplifiers, which in turn are used in others such as instrumentation amplifiers.

amplifier classes

Class A amplifiers are

consuming high continuous flow of power regardless of the existence of signal in the input. This amplification has the disadvantage of generating a strong and constant amount of heat that must be dissipated. This causes a very low yield, to miss an important part energy that goes into it. It is common in audio circuits and high-end home computers, as they provide great sound quality, being very linear, with little distortion.

has a bias current greater than the maximum output current can be delivered. Class A amplifiers often consist of an output transistor connected to the positive terminal of the power supply and a constant current transistor connected from output to negative power supply. When no input signal constant bias current flows directly from positive to negative to negative power supply, power consumed not useful.

Class B

Class B.

Class B amplifiers are characterized by almost zero intensity through their transistors when no input signal circuit. This is what polarizes the transistors to fit in driving area, so consumption is lower than in class A, although the quality is somewhat lower because of the way in which the wave is transmitted. It is used in telephone systems, portable transmitters, security and warning systems, but not audio.

class B amps have output stages with zero bias current. Have a significant distortion with small signals, known as filter distortion, because it occurs at the point where the output stage crosses between the source and the current buffer.

Class C

Class C amplifiers are similar to class B in the output stage has zero bias current. However, they have a region of zero idle current which is over 50% of total supply voltage. The disadvantages of class B amplifiers are more evident in Class C amplifiers This type of amplifier used in audio.

Class AB

Class AB amplifiers are a small constant power at its input, independent of the existence of signal. It is the most common audio at high yield and quality. These amplifiers are named because with large signals behave as a class B, but with small signals behave as a class A.

have two output transistors, such as class B, but unlike them, have a small free stream flowing between the terminals of the power supply, yet not so high as in Class A. This free flow corrects almost all of the nonlinearities associated with the distortion of the filters.

Class D

Class D amplifiers have high energy efficiency, superior in some cases 95%, reducing the size of heat sinks needed, and therefore the overall size and weight of the circuit.

Although previously limited to portable devices or subwoofers, in which distortion or bandwidth, are not determinants with modern technology there are class D amplifiers for the entire frequency band, with distortion levels similar to class AB.

Class D amplifiers are based on switching between two states, which output devices are always on the cutting areas or saturation, cases in which the power dissipated in them is practically nil, except at the transition, the duration must be minimized to maximize performance.

The switching signal can be generated in various ways, but the most common is the pulse width modulation. Then it must be filtered to recover the signal information, for which the switching frequency must be greater than the bandwidth of the signal at least 10 times.

Class D amplifiers require careful design to minimize electromagnetic radiation they emit, and thus avoid interfering with nearby equipment, typically in the FM band.

Other classes

Classes E, G and H are not standardized as A and B. These variations of the classic circuits, which depend on the variation of supply voltage to minimize power dissipation in the power transistors in each time, depending on the input signal.

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EES Section: 02

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1. Introduction

Among the valid signals for digital and analog signals that are normally found in nature is necessary conversion allow digital systems to communicate with the outside.

This communication is passed in two directions:

1. from the digital system to the outside, making a conversion digital / analog (D / A).

2. from the outside to the digital system, making a conversion to an analog / digital (A / D).

There are a lot of converters implemented through a combination

of analog and digital electronics. The choice between one or another design will depend on the performance required for each application.

2. Converting digital / analog (D / A) binary weighted

Let

mount a simple system of digital to analog conversion, which will convert the signal generated by a digital system to obtain an analog signal the output of the circuit. Our digital system will be a counter 74LS93A integrated circuit, very versatile, which allows changing the external connections, configure it to make a note that we truncated at any point in the sequence.

will use to build digital signals that we want to convert, 74LS93A configurations shown in Figure 1 (a reasoned analysis by the integrated block diagram of which is attached, as is generated each sequence):

Figure 1: Set a timer module 16, 10 and 5 respectively

obtained signals Q0, Q1, Q2 and Q3 are digital signals whose value (4 bits) we will convert into an analog signal. The value is a simple digital signal that goes from zero hasta el modulo dado por la configuración respectiva, y por tanto su conversión analógica será una rampa lineal hasta dicho valor. Uno de los conversores D/A más simple es el de ponderación binaria, que se construye mediante una red de resistencias en el que los valores de las resistencias son inversamente proporcionales a los pesos binarios de cada bit digital de la señal de entrada al conversor. Mediante un amplificador operacional, convertimos la intensidad de corriente que circula por cada rama del circuito (y que será proporcional al peso del bit correspondiente), en una señal de voltaje analógica cuyo valor corresponderá al valor binario dado por los cuatro bits de la señal digital. Montar el siguiente circuito for D / A converter will use the given resistance (nominal value then gives slightly from ideal standard shown in the diagram), and integrated operational amplifier LM741. To power the operational amplifier is necessary to connect the integrated power 􀀀 12 V / +12 V, for which we use the two voltage sources interconnected as shown in the figure, creating an intermediate node to ground, which is the basis of land for all the circuit. Feeding the other integrated circuits is between 0 and 5 V, using the TTL power supply voltage. Before connecting the integrated check the polarity of the feeds to the millimeter.

input signals Q0, Q1, Q2 and Q3 of the converter, are the ones that get to the counter output that we connect 74LS93A and respecting the weight of each bit.

After mounting the circuit, perform the following steps:

1. Check, displaying on the oscilloscope signals Q0, Q1, Q2 and Q3, if the sequence generated by the counter in three different configurations are correct.

2. Overlay to display on the oscilloscope clock signal introduced at the counter, and the output signal Vout to get the converter. We must get the correct conversion for the inverted output signal (press and hold the button for the channel 2 on the oscilloscope to see the inverse of Vout), ie, a stepped ramp that increases linearly and becomes

Figure 2: Circuit binary weighting

start after reaching the modulo value for which we set the converter. Make this observation for the three configurations given the counter and graph the signal obtained.

Choose one of the settings of the counter to perform the following steps:

1. Change the value of RVAR and observe its effect on the ramp conversion. Build

a graph that is rendered (for five values) the value of variable resistance and the maximum of the ramp. > It saturates the ramp? Get the maximum value of RVAR for the amplifier is not saturated. Modify slightly (to + -13.5 V) supply of 741 and observe the effect on the conversion. RVAR get the maximum value of -13.5 + V supply.

2. Modify one of the strengths of the resistive network (Eg changing a value slightly higher 2R, using the potentiometer, which we will _ja replaced by a resistance of 100 k) and observe its effect on the ramp conversion. Several different branches and note that steps are modified in each case.

3. Measure time delays for each step of the ramp (with respect to the reference clock signal) and the initialization delay time of conversion (zero ramp). Increasing the clock frequency and see how the signal is distorted. Get the maximum frequency at which the converter operates without errors.

reasonably explain the results of the measures obtained in the last three points.

3. Analog / digital converter (A / D) parallel

in this case is to digitize an analog input signal to obtain the value of the magnitude of the signal expressed by a binary sequence. There are a lot of designs, a wide variety of A / D, whose accuracy depends on the number of output bits by which digitize the signal.

We will set up a simple scan converter in parallel, giving an output of two bits (a limited accuracy), an analog input signal generating a signal that we will get synod with the function generator. We will use four 100 k resistors, three of the four operational amplifiers having the LM324 and a 74LS148 priority encoder. (NOTE: In this case the integrated operational fed with (0, +5 V) and the other, which simplifies the mounting board).

Before mounting the circuit, we will make a trial of digital conversion using a single operational which will control the signal input to the inverting input of the amplifier via the power supply (Vcont), we can modify and convert the analog sine signal introduced by the non-inverting input to a square wave (digital) we obtain at the output. Observe the effect of the value of continuous control signal on output Vcont get (make a sketch of the display of the conversion on the oscilloscope, which will observe the original analog signal and digital signal simultaneously). Observe the delay incurred and obtain the maximum frequency at which the amplifier ceases to scan properly.

After verifying the operational digitizing function, fit the full two-converter bits and display on the oscilloscope the sequence 0 {3 generated by the converter as the analog signal is digitized (using a sine signal ranging from 0 to 4 V).

Figure 3: Setting 74LS148

Note the following issues in the assembly of the figure:

1. The operational with the inverting input connected to the signal we want to digitize and noninverting each of the voltage levels that we have divided the route 0 {VCC. It is the opposite we did in the test with a single operational because in this way we get the scan and we can introduce inverted output signals of the operational input directly to the decoder (inputs denied, active low) for proper operation of A / D converter

2. EI entry serves to introduce a signal that marks the sampling rate. In our case, when connected to LOW (active low) we will carry out continuous sampling, so that the pace of digitization will be marked by operational delays and decoder.

3. The decoder outputs are also active low, so to display them properly on the oscilloscope without using additional investors, we will use the investor's own scope, which is activated by holding down the button a few seconds next to the entrance of the canal.

Given the foregoing, and having verified the correct operation of A / D,

1. Compare the analog signal and each output significant bits (A0 and A1). Make a chart that represents the analog signal and the two bits of output as a function of time. Reason converter operation in two stages: the operational and decoder. Indicate that the decoder should be a priority.

2. On the chart above, study the effect of operational delays by measuring the delay of the intermediate signal on line 3 of entry to the decoder. Calculate the delay by the asymmetry of conversion. Measure the total delay of the decoder, as challenged finding corresponds to the operational and how the decoder.

3. Estimate the precision of digitization.

4. D / A converters and A / D integrated

In electronic systems converters are usually not set built from discrete components of lesser rank, but are used directly integrated circuits containing the full converter, in which all components have been lithographed monolithically in silicon. There is a great deal on the market. Burr-Brown house, which was originally dominated market converters. It has now been absorbed by Texas Instruments, and all products have been included in the catalog of this multinational.

mention two of the most widely used converters, of which I provided some of its spec sheet appended to this practice, although we will not use them.

ADC0804C is an analog-digital converter 8-bit successive approximation monolithic CMOS technology. The conversion is performed by a modified potentiometric network of 256 resistors. Includes flip-flops to control the data bus used, making it very versatile and suitable for inclusion in systems containing microprocessors.

DAC80 is a digital-analog converter 12 bit. Its analog output is very robust and stable, capable of supplying up to 2; 5mA to an external load without degrading the D / A. It also works well in a wide range of temperatures and supply voltages, consuming enough low. Since it is also low cost, this converter is one of the most used.

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EES Section: 02

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The operational amplifier as a control.

describe only that which relates with the regulation. A linear operational amplifier is a high gain with many applications in analog control systems. The figure shows two common types of capsules and the numbering of the pins, the symbol used in diagrams, forms of power and function that meets its output on pin 6.

operational A widely used is the 741 for its wide operating range, with a regular supply +15 volts and -15 volts (with two-way source .) If not using two-way power (Pin 4 connected to ground), the lowest voltage at pin 6 will not reach zero volts since the linearity is lost when approaching the limits of power on pins 4 and 7. An operational saving this problem is for example the CA3140E, responding either from zero volts when the same voltage is applied at pin 4.

As we shall see in the figure, the output of this interesting component is proportional to the difference of the input signals applied to pins 2 and 3 if and when it is not worth more than the supply voltage (positive or negative), after which time it was saturated. Depending on which of the inputs is greater, the output may be positive or negative with respect to the reference voltage or ground (for two-way power). The problem that arises in principle, is that the constant is about one hundred thousand, so a minimum difference between input signals produces the saturation of the operational, appearing at its output a voltage + V o-V (or zero volts if not two-way). The ability to detect small differences in the input signals has many applications, but not at all mentioned in regulation. This problem was easily saved if we do work in closed loop (feeding back the output to one input, which is normally pin 2 for reasons of its inner workings.)

The fact that the gain K is so high is actually a significant advantage when used with feedback. If the formula we set the K value by dividing the output voltage V6, the result will be almost zero, which shows that the operational always tend to equate the two input voltages and their difference is almost zero. Then we will see a few possibilities of operations.

If the operational tends to equalize the two inputs and the output is connected to one of them (a direct feedback as in the first case of the figure below), then the output will always tend to equalize Vs the entry Ve An operational feature of great practical value is that its input impedance is very high and its output is very low, so you can power a load (in vs out) without any change to the behavior of the voltage divider (ratio between the two resistors is equal to the ratio between the two strains on). Remember that when connecting multiple items and one of them is a burden for the former, their behavior varies and can not be studied separately, complicating their study. The purpose shown in the first case in the following figure is therefore to adapt the impedances for the purpose of circuit components or no charge to another. An operational with direct feedback is called a voltage follower.

In the second case of the previous figure we see its application as an inverting amplifier with adjustable gain if the resistance Rs is variable. Although you can connect two in series to provide a non-inverting amplifier, the same is achieved with a single operational (third case of the figure). It is imperative that the amplifier is an investor or investment but can not this be a factor also adjustable (first case in the following figure). As you might expect, these assemblies can play perfectly the role of a proportional controller. Gain formulas shown can be derived by considering the two voltages equal input.
In the second case of the previous figure we see a montage to subtract two signals and applying a gain while the result (by itself includes a comparator and a proportional controller, with the command signal V2 and V1 the feedback). If you only want to use as a receiver is sufficient that R1 and R2 are equal. When necessary to make the sum signal, for example to add two or more actions of a regulator, we use a summing inverter (first case in the following figure) or a non-inverting adder (second case). In the latter case we see how they can join various signals and finally subtract the results.
integral and derivative actions we can obtain as in the following figure. The resistor in parallel with the capacitor (first case) has no role in the signal obtained in the output but simply improving the internal functioning of the operational. The same consideration we do with the condenser of small capacity in the second case.
The following example is a complete PID controller but very simplified, it would present some problems of adjustment parameters and would be more appropriate for a particular application with fixed parameters. However, if we consider the possibilities that have been described not find much difficulty in designing an adjustable regulator.

complete this section showing a single power amplifier (second case in the previous figure) for the supply of small loads (small motors, lamps ...). As might be expected, an operational can not (usually) directly feeding a load. The control output is merely a signal that provides information and must be amplified in power (and voltage normally.)

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EES

Section: 02

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active low pass filter with cutoff frequency operational amplifier, gain

Active filters differ from the common filters in that the latter are only a combination of resistors, capacitors and inductors.

In a common filter, the output is of lesser magnitude than the entry

Instead active filters consisting of resistors, active devices comoAmplificadores Operational capacitoresy otransistores.

In an active filter output can be of equal or greater in magnitude than the input.

active lowpass filter Operational Amplifier

response curve of a low pass filter.

The red dashed lines represent the ideal low pass filter

If the capacitors are selected so that:

C1 = C2 = C, R1 = R2 = R3 = R

The frequency value Fc (cutoff frequency) can be obtained using the following formula: Fc = 0.0481 / RC.

and filter gain (remember that is an amplifier) \u200b\u200bwill be: Av = Vo / Vin = R2 / R1.

If this gain is expressed in decibels: 20log Av = Vo / Vin or Av = 20 log R2 / R1.

Note: Fc (cutoff frequency) is the point in the transfer curve where output has fallen 3 dB (decibels) from its maximum value.

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EES Section: 02

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Oscillators are devices capable of repeating two opposing actions in a period regular. Example: movement a pendulum.

An example of the oscillator in the area of \u200b\u200belectronics, is the change in voltage or current at a specific point.

An LC circuit (inductor-capacitor) is capable of producing this oscillation at its natural frequency of resonance.

oscillators Applications:

- digital circuits (clock)

- Transmission and reception of radio

One type of oscillator called oscillator feedback and swing it should be in the positive feedback circuit.

The characteristics of the oscillators with feedback

Amplification 1 .- 2 .-

positive feedback loop

3 .- Circuit for controlling the frequency

A feedback oscillator is a circuit that uses an amplifier to supply the necessary energy to the oscillator and a feedback circuit to maintain the oscillation. It is in this feedback loop where you lose the power it has to supply the amplifier for the continued operation of the oscillator.

As the swing begins?

The starting voltage is generated by the same components of the oscillator. The resistors generate noise voltage is sinusoidal frequencies higher than 10,000,000,000,000 hertz. When the circuit starts the frequencies generated are amplified and appear at the output excites the resonant circuit that responds only one, which is fed to the input of the circuit with the proper phase to start the operation.

types of oscillators:

- phase shift oscillator

- Oscillator Armstrong (not widely used because of its instability)

- Hartley Oscillator

- Oscillator Colpits

Positive feedback

- Vi = input voltage

- Vo = Output voltage

- B = gain feedback circuit

- Ao = gain open loop amplifier with Ao = Vo / Vi (not taking into account the feedback). See graph

- Vf = voltage feedback

- Ac = closed loop gain

- Bao = The product (B x Ao) is called loop gain

For positive feedback, the closed loop gain is:

Ac = Ao / [1-bao]

If the product B x Ao is close to "1", the denominator of the above formula tends to "0" and consequently gain Ac closed loop tends to infinity. These gains as high oscillations.

phase shift oscillators by

The phase shift oscillators generally used in the feedback network (B) consisting of passive components (resistance and capacitors). See graph.

The amplifier stage (A), is an inverting amplifier with operational amplifier A2, so that your input signal is shifted 180 degrees.

Entondes can use a network (B) three-stage RC (R1C1, R2C2, R3C3. Each RC network moves 60 degrees) for the remaining 180 º and 360 º and add the necessary.

Figure A1 is an amplifier that is used to prevent phase shift network load input inverting amplifier A2. This is so because the amplifier A1 has a high input impedance. The output of A1 is the same phase as its input (it lags).

The oscillation frequency is given by the following formula:

The amplifier A2 provides the gain needed to maintain the oscillation and can be calculated with the formula : Gain = - R5 / R4, where the minus sign means phase reversal. With R2 = R1 = 36K and 1K, the gain is 36.

If the attenuation caused by the RC network, is less than expected, the loop gain is greater than 1 (the open loop gain desabled is 1). The output signal then grows until the amplifier amplified distortion.

As the noninverting input of amplifier A2 is grounded and the inverting input of the amplifier is a virtual ground, the inverting input is kept close to 0 volts.

To prevent the gain is greater than 1, there are two diodes (D1 and D2) that lead when the output sine A2 in the positive direction is greater than 0.7V, and lower negative a - 0.7V.

When the output of A2 is approximately 0.7 V, D1 leads putting resistors R5 and R6 in parallel, the same happens when the signal is approximately -0.7, D2 leads paralleling the same strength. Entoces the gain of A2 is = (R5 / / R6) / R4 = (36k / / 8.2K) / 1K = 6.5. Gain is less than 36 earlier. Thus the output voltage is approximately 1.4V peak to peak.

Note:

- / / means parallel

- A1, A2: general-purpose operational amplifiers IT LM348N (4 operational)

Wein Bridge Oscillator: Gain, feedback network

gain, feedback

Oscillator Wien bridge oscillator is used to generate sine waves ranging from 5 Hz to 5 MHz.

Unlike the phase shift oscillator, has fewer components and adjusting the oscillation frequency is easier, why which is most used.

The basic circuit consists of an amplifier and a network of Adelaide / being late, composed of two RC networks, each series parallel. The two values \u200b\u200bof resistors and capacitors are equal.

Gain

The amplifier gain is given by the resistors R1 and R2.

The gain that must have this amplifier must compensate for the attenuation caused by the RC network (positive feedback network connected to pin noninverting operational amplifier). This gain must be above 1 to ensure oscillation.

gain obtained with the first formula. As the gain must be greater than 1, the equation is simplified and we obtain the second formula:

see that for this to give the ratio of R2 and R1 should be equal to or greater than 2.

Red feedback and lag

The output of the feedback network behaves as follows way:

- For frequencies below the oscillation frequency is large attenuation and phase by 90 °

- A resonant frequency voltage gain is 1 / 3 (maximum) and no phase shift.

- Holm For frequencies of oscillation frequency, the attenuation is large and the phase is delayed 90 °.

Wein Bridge Oscillator

oscillation frequency

To achieve oscillation, it is necessary that the time lag or phase shift is 360 degrees or whatever it is, that the gap is 0 °.

To derive the oscillation formula, follow the steps shown in Fig.

The first equation is that for it to be equal to 0, the contents of paréntesisi must be equal to 0.

The equality of the second equation allows w clear after frequency f. At the end of the simplification is that the frequency depends on the values \u200b\u200bof capacitor C and resistance R. Remember that w = 2Pif

A real Wien bridge oscillator

The values \u200b\u200bof resistors and capacitors of the RC networks, R3 = R4 = 16.2K and C3 = C4 = 0.01uF.

also see the inverting amplifier with resistors R1 and R2 set the gain of the amplifier. R1 = 10K and R2 is made a resistor in series with a potentiometer R2 = R + P. The resistance R = 18K potentiometer P = 5K.

The potentiometer is connected as a variable resistor and when it has its minimum value, (0 ohms), the value of R2 = 18K. When the pot has its maximum value (5K), R2 = 23K.

With these data the amplifier gain varies from 1.8 to 2.3 (greater than 1)

The box formed by the diode bridge and diode aims at limiting zener operational amplifier output to a maximum positive and negative 7 volts to -7 volts.

The diode bridge provides a voltage of 5.6 volts for both the negative cycle and to the positive.

This tension coupled to two voltage drop of two diodes (0.7 +0.7 = 1.4), add the above 7 volts.

Hartley oscillator

The Hartley oscillator is an oscillator type widely used in transistor radios easily adapted to a wide range of frequencies. For his performance this circuit uses a center tapped coil.

Analyzing the diagram, we see that the branch point D of the coil L1, will be grounded for alternating current (AC) (at the oscillation frequency) across the capacitor C4.

In this way we obtain the ends A and B of the coil are 180 ° out of phase (it works as an investor).

The end B is fed to the base of the transistor through C1, causing it (the transistor) changes state, this in turn changes the polarity at the ends of the coil, the process is repeated and thus producing oscillation.

The function of the coil L2 is shock and prevents RF oscillator signal passing to the power supply.

Analyzing the performance of the coil to pass and taking into account that the connection D (central branch) is ground through the capacitor C4, the waveforms at the ends of the coil will be:

The oscillation frequency of this type of oscillator is given by the formula:

for = 1 / [2π x (LC) 1 / 2].

Notes:

- C3 may be a variable capacitor to adjust the oscillation frequency

- The exponent 1 / 2 equals the square root

Colpitts oscillator

The Colpitts oscillator is a type of oscillator is often used in generating high quality and is primarily used for frequencies above 1 MHz. Its stability is higher than the Hartley oscillator.

To achieve this oscillation circuit uses a voltage divider formed by two capacitors, C1 and C2.

From the junction of these capacitors grounded out. Thus the higher terminal voltage of C1 and C2 will lower opposing tensions.

The positive feedback obtained from the lower terminal of C2 and is carried to the base of the transistor through a resistor and a capacitor

L2 coil (choke) is used to prevent the AC signal does not pass the Vcc supply

This oscillator is used for VHF (Very High Frequency) frequencies from 1 Mhz to 30 Mhz.

At these frequencies would be very difficult to use Hartley oscillator because the coils to be used would be very small.

The oscillation frequency of this type of oscillator is given by:

for = 1 / [2π x (LC) 1 / 2]

where :

- C = C1xC2 / [C1 + C2]

- L = L1

Notes:

- R1 can be a variable resistor (potentiometer) to adjust the magnitude of the output signal is fed to the input.

- The exponent 1 / 2 equals the square root.

Mario Dominguez Zambrano

EES Section: 02