Phys 3610/6610 Lab 22
Student:
TA:
An Operational Transconductance Amplifier (OTA) Sample-and-Hold
The task is to use an OTA to construct a sample-and-hold circuit. As you are only allowed to use
one signal generator from the lab, it is advisable that you generate your own 0 to -12 V sample
signal. The signal to be sampled will be a 60 Hz triangular wave of 1 V peak-to-peak amplitude.
You can use the signal generators in the lab to make this signal, or generate it yourself from the
60 Hz square wave and either an op-amp integrator (with no DC response) or a long RC time
constant circuit and an amplifier. It should be noted that the load of a 10x scope probe alone is
small enough that a reasonable sample-and-hold circuit could be built without a follower - but
your circuit should be a useful one capable of driving more than a scope probe. Moreover the
offset due to a non-ideal OTA is reduced if the output of the follower is fed back to the OTA
input. Your notes should discuss the “tilt” (i.e. dVout /dt) of your circuit. Drive IABC at 1 kHz.
You will find it useful to implement your design in steps: Build the OTA part first, then the
follower, and feedback. Document your tests at each step.
This lab refers to the page 20-10 of the lecture notes. It can also be done as shown on page 19-5
of the lecture notes. For the follower you can use either a FET source follower as in the lecture
notes, or any other high input impedance follower. For the FET follower, you must figure out
what circuit changes are needed to use the VN10KM instead of the 3N138 used in the lecture note
circuit.
Remember to block the DC voltage level of the 60 Hz square wave.
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