CONTENTS1. ABSTRACT

1. CHAPTER 1 : INTRODUCTION TO CLIPPERS AND CLAMPERS

1. CHAPTER 2 : CLIPPERS AND CLAMPERS IN GENERAL

1. CHAPTER 3 : ANALYSING CLIPPER AND CLAMPERS

1. REFERNCES

LIST OF FIGURESFIG 1.1(a)INPUT SIGNAL (b)CIRCUIT OF IDEAL DIODE (c)OUTPUT SIGNALFIG 1.2(a)INPUT SIGNAL (b)CIRCUIT OF IDEAL DIODE (c)OUTPUT SIGNALFIG 1.3 CLAMPER CIRCUITFIG 1.4 EXTREME INPUT AND OUTPUT SIGNALFIG 1.5(a)LONG TIME CONSTANT (b)SHORT TIME CONSTANTFIG 1.6 POSITIVE UNBIASED CLAMPERFIG 1.7 NEGATIVE UNBIASED CLAMPERFIG 1.8 POSITIVE BAISED CLAMPERFIG 1.9 NEGATIVE BAISED CLAMPERFIG 1.10 O/P AMPLIFIER CIRCUIT

FIG 2.1 BASIC CLIPPERSFIG 2.2 BAISED SHUNT CLIPPERSFIG 2.3 POSITIVE AND NEGATIVE CLAMPERSFIG 2.4 BAISED CLAMPERSFIG 2.5 ZENER CLAMPERSFIG 2.6 VOLTAGE DOUBLES

FIG 3.1 CLAMPER 1FIG 3.2 CLAMPER 2FIG 3.3 CLAMPER 3FIG 3.4 CLAMPER 4FIG 3.5 CLAMPER 5FIG 3.6 CLAMPER 6

ABSTRACTA clipper circuit for clipping an upper portion and/or lower portion of a unidirectional sinusoidal voltage signal. The clipper circuit comprises a unidirectional buffer amplifier biased to either a (+) or (-) voltage for taking a sinusoidal voltage signal with only a (+) or (-) band value as an input voltage signal, a first Zener diode whose anode is connected to an output port ofsaid unidirectional buffer amplifier and cathode is connected to a predetermined voltage source for clipping the lower portion of the input voltage signal as a predetermined setting value, and a second Zener diode whose cathode is connected to the output port of the unidirectional buffer amplifier and whose anode is grounded for clipping the upper portion of the input voltage signal as a predetermined setting value.

CHAPTER 1INTRODUCTION TO CLIPPERS & CLAMPERSCLIPPERS Clipping circuits (also known as limiters, amplitude selectors, or slicers),are used to remove the part of a signal that is above or below some defined reference level. Weve already seen an example of a clipper in the half-wave rectifier that circuit basically cut off everything at the reference level of zero and let only the positive-going (or negative-going) portion of the input waveform through.To clip to a reference level other than zero, a dc source is put in series with the diode. Depending on the direction of the diode and the polarity of the battery, the circuit will either clip the input waveform above or below the reference level (the battery voltage for an ideal diode; i.e., for Von=0). This process is illustrated in the four parts of Figure : 1. Without the battery, the output of the circuit below would be the negative portion of the input wave (assuming the bottom node is grounded). When vi > 0, the diode is on (short-circuited), vi is dropped across R and vo=0. When vi VB. This shifts the reference level up and clips the input at +VB and passes everything for vi < VB.

Figure1.2 (a) input signal ,(b): circuit for ideal diode ,(c): output signal has the battery with the same orientation as in part (a), but the diode has been flipped. Without the battery, the positive portion of the input waveform would be passed (i.e., a reference level of zero). With the battery, the diode conducts for vi < VB. This means that the reference level is shifted to +VB and only vi > VB appears at the output.

Again referencing part, the diode is in the original position but the polarities on the battery have been switched . The discussion follows the same logic as earlier, but now the reference level has been shifted to VB. The final result is that vo = vi for vi < -VB.

Finally, behaves the same as, but the polarity on the battery has been switched, shifting the reference level to -VB. The signal that appears as the output is vi as long as vi > - VB.

A series-biased clipper involves placing a battery in series with the input. The result of this modification is that the input signal is no longer symmetric about the zero axis, but instead shifts by an amount defined by the magnitude and polarity of VB. In Figure 3.46, the four possible permutations and the resulting output waveforms are shown for an ideal diode. When you look at this figure, keep in mind that the input signal is swinging between +2 and 2 volts and the battery magnitude VB is 1 volt. This may avoid some confusion when looking at the output waveforms the (2V+VB) is just 3 volts and the (2V-VB) may be replaced by 1 volt. The series placement of the battery is not changing the input waveform in any way, it is simply affecting when the diode turns on. To include the effects of a practical diode, include VON and RF in the diode path and crunch the math.

Clampers Clamping circuits, also known as dc restorers or clamped capacitors, shift an input signal by an amount defined by an independent voltage source. While clippers limit the part of the input signal that reaches the output according to some reference level(s), the entire input reaches the output in a clamping circuit it is just shifted so that the maximum (or minimum) value of the input is clamped to the independent source. Lets look at Figure 3.48 (input and circuit shown to the right) and see if we can turn this into something that makes sense! Basically, we have a sinusoidal input of magnitude Vm with zero offset (i.e., symmetric signal) fed to the clamper circuit. Taking the input by sections to build the output

Figure 1.3 : clamper circuit If vin > VB, the diode is on, R is shorted, and the output is VB. 1. When vin < VB, the diode is off, current flows through the resistor, and the capacitor charges to a voltage vac=VB vin. The maximum voltage on the capacitor will be related to the maximum swing of the input by: 1. After fully charging, the capacitor acts like series source in the circuit (with the RC time constant conditions discussed below). After steady state is reached, the output voltage is found by loop analysis as Vc = Vm VBVo= Vin + Vc. In the circuit shown above, Vc = Vm +V (KVL at maximum negative input, Vin=-Vm) or Vo = Vin Vm + VB. Specifically, for the extreme values of the input signal: if Vin=+Vm, Vo=VB, and if Vin=-Vm, Vo=-Vm Vm + VB = -Vm (Vm VB) = -Vm + VC = VC Vm (Whew! I went through all that to get something that looked like it belonged to the figure to the right!). Keep in mind that the above analysis was for the diode orientation and VB polarity shown. If the diode had been flipped, the minimum rather than the maximum of the input would have been clamped to VB. Figure 1.4 : extreme i/p & o/p signal A clamping circuit has to have an independent source, a diode, a resistor and a capacitor. To keep a constant voltage on the capacitor over the period of the input, the RC time constant must be large. A design rule of thumb is to make the RC time constant at least five times the half-period of the input signal, which results in approximately an 18% error over a half-period due to capacitor discharge. If this error is too large, the RC time constant may be increased but, as with everything in design, there comes a point where factors such as size and power dissipation may make any further improvements impractical. Following our discussion above for illustrates a circuit that will clamp a square wave to zero Parts (b) and (c) of this figure, shown below, demonstrate the output of the clamper with a long time constant and the distortion introduced by the capacitor discharging for a short time constant. It is noted in your book that this square wave may be considered a worst-case situation since it places the greatest demands on a clamping circuit due to the instantaneous changes in the waveform. (Remember from your discussions of harmonics and signal composition, that instantaneous change requires infinite frequencies.)

Figure 1.5

Positive unbiased voltage clamping shifts the amplitude of the input waveform so that all parts of it are greater than 0V.Aclamperis anelectronic circuitthat fixes either the positive or the negative peak excursions of a signal to a defined value by shifting its DC value. The clamper does not restrict the peak-to-peak excursion of the signal, it moves the whole signal up or down so as to place the peaks at the reference level. Adiode clamp(a simple, common type) consists of adiode, which conducts electric current in only one direction and prevents the signal exceeding the reference value; and acapacitorwhich provides a DC offset from the stored charge. The capacitor forms atime constantwith theresistorload which determines the range of frequencies over which the clamper will be effectively.

General functionA clamping circuit (also known as a clamper) will bind the upper or lower extreme of a waveform to a fixed DC voltage level. These circuits are also known as DC voltage restorers. Clampers can be constructed in both positive and negative polarities. When unbiased, clamping circuits will fix the voltage lower limit (or upper limit, in the case of negative clampers) to 0 Volts. These circuits clamp a peak of a waveform to a specific DC level compared with a capacitively coupled signal which swings about its average DC level.

Clamp circuits are categorised by their operation; negative or positive, and biased or unbiased. A positive clamp circuit outputs a purely positive waveform from an input signal; it offsets the input signal so that all of the waveform is greater than 0V. A negative clamp is the opposite of this - this clamp outputs a purely negative waveform from an input signal.A bias voltage between the diode and ground offsets the output voltage by that amount.For example, an input signal of peak value 5V (VIN= 5V) is applied to a positive clamp with a bias of 3V (VBIAS= 3V), the peak output voltage will be:VOUT= 2VIN+ VBIASVOUT= 2 * 5V + 3VVOUT= 13V

Positive unbiased

Figure 1.6A positive unbiased clampIn the negative cycle of the input AC signal, the diode is forward biased and conducts, charging the capacitor to the peak positive value of VIN. During the positive cycle, the diode is reverse biased and thus does not conduct. The output voltage is therefore equal to the voltage stored in the capacitor plus the input voltage gain, so VOUT= 2VIN

Negative unbiased

Figure 1.7A negative unbiased clampA negative unbiased clamp is the opposite of the equivalent positive clamp. In the positive cycle of the input AC signal, the diode is forward biased and conducts, charging the capacitor to the peak value of VIN. During the negative cycle, the diode is reverse biased and thus does not conduct. The output voltage is therefore equal to the voltage stored in the capacitor plus the input voltage again, so VOUT= -2VIN

Positive biased

Figure 1.8A positive biased clampA positive biased voltage clamp is identical to an equivalent unbiased clamp but with the output voltage offset by the bias amount VBIAS. Thus, VOUT= 2VIN+ VBIAS

Negative biased

Figure : 1.9A negative biased clampA negative biased voltage clamp is likewise identical to an equivalent unbiased clamp but with the output voltage offset in the negative direction by the bias amount VBIAS. Thus, VOUT= -2VIN- VBIAS

Figure 1.10 Op-amp circuit An op-amp clamp circuit with a non-zero reference clamping voltage. The advantage here is that the clamping level is at precisely the reference voltage. There is no need to take into account the forward volt drop of the diode (which is necessary in the preceding simple circuits as this adds to the reference voltage). The effect of the diode volt drop on the circuit output will be divided down by the gain of the amplifier, resulting in an insignificant error.Clamping for input protectionClamping can be used to adapt an input signal to a device that cannot make use of or may be damaged by the signal range of the original input.Principles of operationThe schematic of a clamper includes a capacitor, followed by a diode in parallel with the load. The clamper circuit relies on a change in the capacitor's time constant; this is the result of the diode changing current path with the changing input voltage. The magnitude ofRandCare chosen so that the time constant,, is large enough to ensure that the voltage across the capacitor does not discharge significantly during the diode's non-conducting interval. On the other hand the capacitor is chosen small enough to allow it to charge quickly during the diode's conducting interval.

During the first negative phase of the AC input voltage, the capacitor in the positive clamper charges rapidly. AsVinbecomes positive, the capacitor serves as a voltage doubler; since it has stored the equivalent ofVinduring the negative cycle, it provides nearly that voltage during the positive cycle; this essentially doubles the voltage seen by the load. AsVinbecomes negative, the capacitor acts as a battery of the same voltage ofVin. The voltage source and the capacitor counteract each other, resulting in a net voltage of zero as seen by the load.

Biased versus non-biasedBy using a voltage source and resistor, the clamper can be biased to bind the output voltage to a different value. The voltage supplied to the potentiometer will be equal to the offset from zero (assuming an ideal diode) in the case of either a positive or negative clamper (the clamper type will determine the direction of the offset. If a negative voltage is supplied to either positive or negative, the waveform will cross the x-axis and be bound to a value of this magnitude on the opposite side. Zener diodes can also be used in place of a voltage source and potentiometer, hence setting the offset at the Zener voltage.

Clamping circuit were common inanalog televisionreceivers. These sets have a DC restorer circuit, which returns the voltage of the signal during the back porch of the line blanking period to 0V. Low frequency interference, especially power line hum, induced onto the signal spoils the rendering of the image, and in extreme cases causses the set to losesynchronization. This interference can be effectively removed via this method.

CHAPTER 2CLIPPERS AND CLAMPERS IN GENERALCLIPPERSA clipper is a circuit that is used to eliminate a portion of an input signal. There are two basic types of clippers: series clippers and shunt clippers. the series clipper (left) contains a diode that is in series with its load. The shunt clipper (right) contains a diode that is in parallel with its load.

FIGURE: 2.1 Basic clippers.The series clipper is a familiar circuit. The half-wave rectifier is nothing more than a series clipper. When the diode in the series clipper is conducting, the load waveform resembles the input waveform. When the diode is not conducting, the output is approximately 0 V. The physical orientation of the diode determines the polarity of the output waveform. When the diode points toward the source, the circuit is a positive series clipper, meaning it clips the positive alternation of the input waveform. When the diode points toward the load, the circuit is a negative series clipper, meaning that it clips the negative alternation of the input.Ideally, a series clipper has an output of VL = Vin when the diode is conducting (ignoring the voltage across the diode). When the diode is not conducting, the input voltage is dropped across the diode, and VL = 0 V. Unlike a series clipper, a shunt clipper provides an output when the diode is not conducting.When the diode is off (not conducting), the component acts as an open. When this is the case, RS and RL form a voltage divider, and the output from the circuit is found using

When the diode in the circuit is on (conducting), it shorts out the load. In this case, the circuit ideally has an output of VL = 0 V. Again, this relationship ignores the voltage across the diode. In practice, the output from the circuit is generally assumed to equal 0.7 V, depending upon whether the circuit is a positive shunt clipper or a negative shunt clipper. The direction of the diode determines whether the circuit is a positive or negative shunt clipper. The series current-limiting resistor (RS) is included to prevent the conducting diode from shorting out the source. A biased clipper is a shunt clipper that uses a dc voltage source to bias its diode. Two biased clippers are shown in . The biasing voltage (VB) in each circuit determines the voltage at which diode conduction begins. For example, the diode in begins conducting when the load voltage reaches (VB + 0.7 V). The diode in begins conducting when the load voltage reaches (-VB - 0.7 V). In practice, the dc biasing voltage is usually set using a dc power supply and potentiometer.

FIGURE 2.2 Biased shunt clippers.Clippers are used in a variety of systems, most commonly to perform one of two functions: 1. Altering the shape of a waveform 1. Protecting circuits from transients The first application is apparent in the operation of half-wave rectifiers. As you know, these circuits are series clippers that change an alternating voltage into a pulsating dc waveform. A transient is an abrupt current or voltage spike of extremely short duration. Left unprotected, many circuits can be damaged by transients. Clippers can be used to protect sensitive circuits from the effects of transients, as illustrate of the text. Clampers (DC Restorers) A clamper is a circuit designed to shift a waveform above or below a dc reference voltage without altering the shape of the waveform. Two clampers are shown in : 1. A negative clamper shifts its input waveform in a negative direction, so that it lies below some dc reference voltage. (For example, if we assume the center of the oscilloscope grid in is calibrated to 0 V, the clamper input waveform is shifted below 0 V.) 1. A positive clamper shifts its input waveform in a positive direction, so that it lies above some dc reference voltage. The type of clamper (positive vs. negative) is determined by the physical orientation of the diode.

FIGURE 2.3 Positive and negative clampers.Clamper operation is based on the concept of switching time constants. The capacitor charges through the diode and discharges through the load. As a result, the circuit has two time constants:1. For the charge cycle, = RDC and TC = 5RDC (where RD is the resistance of the diode) 1. For the discharge cycle, = RLC and TD = 5RLC (where RL is the resistance of the load) Since RL is normally much greater than RD, the capacitor charges much more quickly than it discharges. As a result, the input waveform is shifted as illustrated in of the text. A biased clamper allows a waveform to be shifted above (or below) a dc reference other than 0 V. Each biased clamper uses a dc supply voltage (VB) and a potentiometer to set the potential at the cathode of D1. By varying the setting of R1, the circuit reference voltage can be varied between approximately 0 V and the value of VB.

FIGURE 2.4 Biased clampers.

The zener clamper uses a zener diode to set the circuit dc reference voltage. For example, the dc reference voltage for each zener clamper has a value of VZ 0.7 V.

FIGURE 2.5 Zener clampers.Voltage Multipliers

FIGURE 2.6 Voltage doublers.A voltage multiplier provides a dc output voltage that is a multiple of the circuits peak input voltage. For example, a voltage doubler with a peak input of 10 V provides a dc output that is approximately 20 V. Two voltage doublers .Each of the circuits provides a dc load voltage that is approximately twice the value of the peak source voltage. The half-wave doubler gets its name from the fact that the output capacitor (C2) is charged during the positive half-cycle of the input signal, of the text. In contrast, the output capacitor in the full-wave doubler (C3) is charged during both alternations of the input cycle, Note that the output from a full-wave doubler has less ripple than the output from a comparable half-wave doubler.The voltage tripler is very similar to the half-wave voltage doubler. If you compare the tripler to the circuit in , youll see that the combination of C1, C2, D1, and D2 forms a half-wave voltage doubler. This circuit charges C2 to a value of 2VS(pk). During the negative alternation of the input cycle, C3 is charged to approximately VS(pk). The voltage across the series combination of C2 and C3 is approximately 3VS(pk). Since C4 and the load are in parallel with the series combination of C2 and C3, VC4 and VL are also approximately equal to 3VS(pk).

FIGURE 4.7 A voltage tripler.

The voltage quadrupler contains two half-wave voltage doublers, as shown in Figure 4.8. The circuit made up of C1, C2, D1, and D2 charges C2 to a value of 2VS(pk). The circuit made up of C3, C4, D3, and D4 charges C4 to a value of 2VS(pk). The combined charge of 4VS(pk) is applied to C5 (the filter capacitor) and the load.

FIGURE 4.8 A voltage quadrupler.Voltage multipliers reduce source current by roughly the same factor that they increase source voltage. For example, a voltage tripler produces a dc output voltage that is approximately three times the peak source voltage. At the same time, its maximum output current is roughly one-third the value of the source current. As such, voltage multipliers are commonly used in high-voltage, low-current applications. They can also be used to produce dual-polarity output voltages in power supply applications.

LED ApplicationsLEDs are most commonly used as power indicators, level indicators, and as the active elements in multisegment displays.The power indicator on any electronic component is most likely an LED. When the component is turned on, power is supplied to the LED. The LED lights, indicating that the component is on. A level indicator is used to indicate when a signal voltage reaches a designated level. LEDs are most commonly used in multisegment displays. These displays are used to display alphanumeric symbols, such as letters, numbers, and punctuation marks. A seven-segment display and several other multisegment displays .Each type of display is available in either a common-anode or common-cathode configuration. A common-anode display has a single anode (+V) input that is applied to all the LEDs in the display. Individual segments are lighted by providing a ground path to the appropriate cathodes. In contrast, a common-cathode display has a single cathode (ground) pin that is connected to all LEDs in the display. Individual segments are lighted by providing a +V input to the appropriate anodes. Note that many multisegment displays require a current-limiting resistor in series with each LED in order to restrict device current. Another type of multisegment display, called a liquid-crystal display (LCD), contains segments that reflect (or do not reflect) ambient light. LCDs typically require less power than LED displays and thus are better suited for use in low-power electronic systems, such as portable phones.

Diode Circuit TroubleshootingA variety of fault symptom tables are listed in this chapter for clippers, clampers, multipliers, and displays:1. Shunt clipper faults, 1. Clamper faults, 1. Additional biased-clamper faults, 1. Additional zener-clamper faults, 1. Voltage multiplier faults, Multisegment displays are often controlled by ICs called decoder-drivers. These ICs provide the active +V (or ground) inputs required for the individual segments. The most common multisegment display fault is the failure of one or more segments to light. When this occurs, check the input to the common pin. Assuming that the potential there is correct, check the inputs from the decoder-driver. If the inputs to the display are correct, the display must be replaced. If not, the decoder-driver (and current-limiting resistor) must be tested.

CHAPTER 3ANALYZING CLIPPERS AND CLAMPERSPOSITIVE CLAMPER

CLAMPER 1:

The input to the circuit is sine wave here.

Figure 3.1: clamper 1In the first +ve cycle of the diode D is reverse bias.

During the first ve cycle of the input the diode D is forward bias. Current in the circuit will flow from point B-D-C-A. This will charge capacitor C in the shown polarity to the peak input voltage (Vm). Applying KVL in ve cycle. Capacitor Voltage Vc is Vm.

Now Applying KVL in +ve cycle.

The circuit has a output in which the waveform is shifting up thus it is called Positive Clamper.

Drawing output of Circuit Below (Biased Clamper):

CLAMPER 2:

Figure:3.2 clamper 2

During +ve Cycle, Apply KVL

CLAMPER 3:

Figure 3.3 :clamper 3

During ve cycle

Negative clamper

If we turn the diode, the polarity of capacitor voltage reverses and the circuit becomes negative Clamper.

Drawing output of Circuit Below:

CLAMPER 4:

Figure 3.4 : clamper 4

CLAMPER 5:

Figure 3.5 : clamper5

During +ve cycle

CLAMPER 6: Figure 3.6 : clamper 6

To calculateVc

To Calculate Vo

REFERENCES

1. Analog Electronics -by SANJAY SHARMA2. www.electronicsforyou.com3. www.electronicsengineering.com4. www.electronictutorial.com5. Integrated Electronics -by MILLIMAN AND HALKAIS 6. Discovery in Electronics7. www.integratedelectronics.net8. Electrical and Electronics Engineering Forum9. Electronics Dept. of MNIT10. ABC of Physics - XII Class -by SATISH K GUPTA