LINEAR INTEGRATED CIRCUITS
LINEAR INTEGRATED CIRCUITS
Course Objectives:
Ø Design of OPAMPS, Classification of OPAMPs.
Ø To study and design various linear applications of OPAMPs.
Ø To study and design various non linear applications of OPAMPs
Course Outcomes:
Ø Understand the basic
building blocks of linear integrated circuits and its characteristics.
Ø Analyze the linear,
non-linear and specialized applications of operational amplifiers.
Ø Understand the theory of ADC and DAC.
Ø Realize the importance of Operational
Amplifier.
Sample and Hold Circuit
The sample and hold circuit, as
its name implies samples an i/p signal and holds on to it last sampled value
until the i/p is sampled again. Below fig shows a sample and hold circuit using
an op-amp with an E- MOSFET. In this circuit the E-MOSFET works as a switch
that is controlled by the sample and control voltage Vs, and the capacitor C
serves as a storage element.
The analog signal Vin to be
sampled is applied to the drain, and sample and hold control voltage Vs is
applied to the gate of the E-MOSFET. During the positive portion of the Vs, the
EMOSFET conducts and acts as a closed switch. This allows i/p voltage to charge
capacitor C. In other words input voltage appears across C and in turn at the
o/p as shown in above fig.2.9.On the other hand, when Vs is zero, the EMOSFET
is off and acts as open switch. The only discharge path for C is, through the
op-amp. However the i/p resistance of the op-amp voltage follower is also very
high; hence the voltage across C is retained.
The time periods Ts of the sample-and-hold control
voltage Vs during which the voltage across the capacitor is equal to the i/p
voltage are called sample periods. The time periods TH of Vs during which the
voltage across the capacitor is constant are called hold periods. The o/p of
the op-amp is usually processed/ observed during hold periods. To obtain the
close approximation of the i/p waveform, the frequency of the sample-and-hold
control voltage must be significantly higher than that of the i/p.
Fig.1.30: sample and hold circuit Fig
1.38 I/P and O/P wave forms
