# Linear IC’s and Applications August 2002

Note: Answer any FIVE full questions.

1.  (a) For an emitter coupled differential amplifier obtain an expression for the common mode reflection ratio (CMRR)

(b) Briefly explain the purpose of a constant current source in a differential amplifier.

(c) What is thermal drift? How compensation is obtained in differential amplifier.

2. (a) Define the following terms with respect to op .amp. 741C and give their typical values. i) Input offset current ii) Slew rate iii) PSRR iv) Input offset voltage.

(b) Show how an op amp. can be used as an integrator and a differentiator by obtaining the expression for output voltages.

(c) Design an op.amp. Schmitt trigger circuit with UTP = 2V, LTP = IV, supply voltage = ± 15V, Vgaf = ±12V
3. (a) Draw the circuit diagram of a monostable multivibrator using op.amp and

derive an expression for the output pulse width, giving the waveforms.

(b) What are the advantages of active filters over passive filters.

(c) Design an active high pass filter to meet the following specifications.

i) Butterworth response

ii) Cutoff frequency = 4KHz

iii) Decay rate in the stop band = 40dB/decase.

(a) Show how a 555 IC timer can be used as an astable multivibrator.

(b) Explain the principle of operation of a Sample and Hold Circuit. (5 Marks)

(c) With a neat circuit diagram explain the working of a Dual Slope Analog to digital converter mentioning its uses.
4. (a) Explain the following terms with reference to digital to analog converter

i)  Resolution ii) Linearity iii) Accuracy iv) Settling time v) Stability.

(b) A 4 bit digital ramp ADC has an input range of 0 to 7.5 volts. Estimate

i) Resolution

ii) Digital output for an input of 4.25 volts

iii) Conversion time if the clock frequency is IMHz

5  (a)What is the limitation of an ordinary PN junction in rectifier applications ? (b)Explain how an inverting amplifier can be converged to an idial half-wave- rectifier with necessary illustrations.

(c) What is an analog multiplier ?; When do you say that the multiplier is a one quadrant multiplier ? Name the applications of a multiplier. With a block schematic briefly explain a log – antilog multiplier.

(d) Explain the operation of a positive peak detector.  What are the problems faced by the designer in the design of an analog fitter?

6 (a) How are these problems overcome in an active filter ?

(b)Write the circuit of a narrow band band pass filter using a single OPAMP in the inverting mode. Considering its generalised form, deduce expressions for the following :

i)  transfer function for the filter at resonance.

ii)  the bandwidth

(c) Design a BPF using a single OPAMP to meet the following characteristics : Lower cut-off frequency /01 = ZKHz Upper cut-off frequency /02 = 3.5KHz

Gain at resonant frequency is -5

7 (a)Briefly explain the basic block diagram of the 555 timer. Ilustrate the external connections required to design a free-running multi­vibrator using the 555 timer and derive the equation for the frequency of oscillations.

(b) Explain how a PLL can be used to detect an AM signal.

(c) How are ADCs broadly classified ? On what principle do they work ?

8 (a)With a neat schematic and necessary waveforms, explain the operation of the basic voltage – to- frequency ADC circuit.

(b) Discuss briefly the specifications of analog – to – digital converters.  Calculate the values of LSB, MSB, and full scale output for a 12 – bit DAC, for 0-10 volts.

(c) Explain briefly the following :

a)     OPAMP schmitt trigger

b)     Sample and Hold circuit

c)         fiA723 regulator