Clippers_and_Clampers.pptx

clippers and clampers

1. Clippers and Clampers

2. Diode limiters/clippers – that limits/clips the portion of signal voltage above or below certain level. Limiting circuits limit the positive or negative amount of an input voltage to a specific value. 4 basic clipper configuration: Negative series clipper diode is in series with its load Positive series clipper Negative shunt clipper diode is in parallel with its load Positive shunt clipper 2 Diode Clipping & Clamping Circuits (Diode Clipper)

3. 3 Clipper configuration Diode Clipping & Clamping Circuits (Diode Clipper)

4. Positive series clipper Diode is reverse-biased during +ve alternation of i/p signal. Diode is forward-biased when i/p signal is –ve. Eliminates positive alternation of its input. 4 Negative series clipper Diode is forward-biased during +ve alternation of i/p signal. Diode is reverse-biased when i/p signal is –ve. Eliminates negatives alternation of its i/p. Diode Clipping & Clamping Circuits (Diode Clipper)

5. Negative shunt clipper Reverse-biased diode act as open cct during +ve cycle. Forward-biased diode act as short cct during –ve cycle. o/p signal is limit/clip to -0.7V during –ve cycle of i/p signal. Positive shunt clipper Forward-biased diode when i/p is +ve cycle. Reverse-biased diode when i/p is in –ve cycle. o/p signal is limit/clip to +0.7V during +ve cycle of i/p signal. 5 Diode Clipping & Clamping Circuits (Diode Clipper)

6. Series clipper When diode in –ve series clipper is FB, load voltage is: V L =V in – 0.7V When diode is RB, doesn’t conduct, so: V L = 0V +ve series clipper operates the same. The only differences are: O/p voltage polarities are reversed. V L =-V in + 0.7V Current direction through cct are reversed. Shunt clipper For – ve shunt, when i /p signal + ve cycle, diode is RB (open circuit), thus: During – ve cycle, diode is FB, load voltage is equal to diode forward voltage. V L = -V F = -0.7V For + ve shunt, o/p voltage and current direction are reversed. 6 Diode Clipping & Clamping Circuits (Diode Clipper)

7. 7 What would you expect to see displayed on an oscilloscope connected across RL in the limiter shown below. The diode is forward biased and conducts when input voltage goes below -0.7V. So, for – ve limiter, the peak output voltage across RL is : Diode Clipping & Clamping Circuits (Diode Clipper)

8. 8 Biased Clippers : 2 type of biased Clipper: 1) P ositive-biased Clipper 2) N egative-biased Clipper P ositive biased Clipper The voltage at point A must equal V BIAS +0.7V before diode become FB and conduct. Once diode begin to conduct, voltage at point A is limited to V BIAS +0.7V, so all i/p voltage above this level is clipped off. Negative biased Clipper Voltage at point A must go below –V BIAS - 0.7V to forward-bias the diode and initiate limiting action. A positive limiter A negative limiter Diode Clipping & Clamping Circuits (Diode Clipper)

9. Parallel Biased Clippers Positive and negative clipping can be performed simultaneously by using a double limiter or a parallel-based clipper. The parallel-based clipper is designed with two diodes and two voltage sources oriented in opposite directions. This circuit is to allow clipping to occur during both cycles; negative and positive Diode Clipping & Clamping Circuits (Diode Clipper)

10. 10 Example 5: Sketch the output voltage waveform as shown in the circuit combining a positive limiter with negative limiter in Figure 5-1. Figure 5-1 + 15V - 15V 6 V 6 V Diode Clipping & Clamping Circuits (Diode Clipper)

11. 11 Clipper Circuits Summary

12. Clipper Circuits Summary 12

13. Half-wave rectifier Circuit alters the shape of ac signal and change it to pulsating dc. Transient protection circuit Transient  abrupt current or voltage spike in short duration. Many digital circuits have i/p that cannot tolerate voltage fall outside a specified range which can cause serious damage. A clipper can be used to protect these circuits. AM detector Eliminate –ve portion of i/p waveform, so capacitor charges and discharges at rate of peak i/p variations. This provides a signal at load that is a reproduction of i/p signal. 13 Diode Clipping & Clamping Circuits (Diode Clipper)

14. Shift a waveform either above or below a given reference voltage without distorting the waveform. Clamp a signal to a different dc level. known as DC restorers. used in TV Receivers as a DC Restorer. The network consists of: a) Capacitor b) Diode c) Resistive element d) Independent dc supply (option) T= RC is large enough to ensure that the voltage across the capacitor does not discharge significantly during the interval the diode is nonconducting. Our analysis basis that all capacitor is fully charge and discharge in 5 time constant. 14 Diode Clipping & Clamping Circuits (Diode Clamper)

15. Types: 2) Negative Clamper 1) Positive Clamper Diode Clipping & Clamping Circuits (Diode Clamper)

16. Diode Clipping & Clamping Circuits (Diode Clamper) Clamping Circuit Theorem   This theorem enables us to calculate the voltage level to which theoutput is clamped by considering the areas above and below thereference level, when the values of R f   and R are known.   The clamping circuit theorem states that under steady-state conditions,for any input waveform, the ratio of the area under the output voltagecurve in the forward direction to that in the reverse direction is equal tothe ratio Rf /R.                                                                                                                                                                                                           Clamping Circuit Theorem: This theorem enables us to calculate the voltage level to which the output is clamped by considering the areas above and below the reference level, when the values of Rf and R are known. The clamping circuit theorem states that under steady-state conditions, for any input waveform, the ratio of the area under the output voltage curve in the forward direction to that in the reverse direction is equal to the ratio Rf /R.

17. To prove the clamping circuit theorem, consider a typical steady-state output for the clamping circuit, represented below: Diode Clipping & Clamping Circuits (Diode Clamper)

18. Diode Clipping & Clamping Circuits (Diode Clamper)

19. Diode Clipping & Clamping Circuits (Diode Clamper)

20. Diode Clipping & Clamping Circuits (Diode Clamper)

21. When the diode is forward biased ,the capacitor charges. where R D is bulk resistance of the diode and C is capacitance of the capacitor. The total charge time is: (a) Capacitor charge circuit Clamper Operation Diode Clipping & Clamping Circuits (Diode Clamper)

22. 22 When the diode is reverse biased, the capacitor starts to discharge through RL. Therefore, the discharge time constant is found as: and the total discharge time is found as: The capacitor retains a charge approximately equal to the input peak less the diode drop so that it acts as a battery. Fig.: Positive clamper operation Reverse-biased Diode Clipping & Clamping Circuits (Diode Clamper)

23. 23 Operation of clamper + ve region 0 - T/2: Diode is ON state (short-ckt equivalent) Assume RC time is small and capacitor charge to V volts very quickly Vo=0 V (ideal diode) - ve region T/2- T: Diode is OFF state (open-ckt equivalent) Both for the stored voltage across capacitor and applied signal current through cathode to anode KVL: - V- V- Vo = 0 and Vo = -2V Total swing o/p signal = the total swing i/p signal

24. 24 Fig: Negative clamper operation Diode Clipping & Clamping Circuits (Diode Clamper)

25. STEP 1 : Knowing what value that the capacitor is charged to. And from the polarity of the diode , we know that it is charged during positive cycle. Using KVL, V C + V B – V S = 0  V C = V M – V B STEP 2 : When the diode is reversed biased and V C is already a constant value V O – V S + V C = 0  V O = V S – V C . A clamping circuit that includes an independent voltage source V B . Peak value V M Diode Clipping & Clamping Circuits (Diode Clamper)

26. C + Vo - 5V + Vi - Vi t -10 10 The diode is a non-ideal with V  = 0.7V Step 1: V C + V  - V B – V i = 0  V C = 10 + 5 – 0.7 = 14.3V Step 2: V O – V i + V C = 0  V O = V i – 1 4.3. -4.3 -24.3 -14.3 Diode Clipping & Clamping Circuits (Diode Clamper)

27. EXAMPL-clampers with ideal diode: For the circuit shown in figure below, sketch the waveforms of the output voltage, V out . The input voltage is a sine wave where V in = 20 sin  t. Assume ideal diodes. Vin Diode Clipping & Clamping Circuits (Diode Clamper)

28. 28 Step 1: Consider the part of i/p signal that will forward bias the diode. From network (t1-t2:-ve region) Step 2: During ON state assume capacitor will charge to a voltage level determined by the network. Find the store voltage capacitor & obtained Vo KVL: -20 +Vc – 5 = 0 Vc = 25v Vo = 5 Diode Clipping & Clamping Circuits (Diode Clamper)

29. 29 Step 3: During OFF state assume capacitor will hold on its established voltage level. From network (t2-t3:+ve region) + R=100 kohm Vo - + - 10 V C Vc 5 V KVL Step 4: Obtained Vo Diode Clipping & Clamping Circuits (Diode Clamper)

30. Step 5: Checking!!! total swing o/p signal = total swing i/p signal From network (t2-t3: +ve region) 30 Diode Clipping & Clamping Circuits (Diode Clamper)

31. Summary of Clamper Circuits 31