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#analog-design
Title
# analog-design
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Shabarish Nayakanti

11/05/2020, 2:07 PM
Hie, actually I was trying to design an Op-amp but facing a lot of issues but somehow I managed to get a clean output without any distortion but I am getting functionality error like giving 1milli sine wave at the positive terminal I was expecting square wave with saturated voltages in output but I am getting inverted sine output with some DC added Can someone please help in that
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yrrapt

11/05/2020, 5:20 PM
Can you post the schematic?
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Shabarish Nayakanti

11/05/2020, 6:22 PM
Screenshot (423).png
using nfet for M2(Common drain configuration) is giving normal sine(non-inverted) but wave is distorted like small ramp signal on it and DC is also addded
i was testing it in comparator mode
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yrrapt

11/05/2020, 7:17 PM
Operating it like this with no feedback is not the normal way to try and amplify signals. And there will be an DC offset at the bias of the output but this will be very badly defined without feedback
The biasing is not really the normal way to do it because it relies on the gm of M9. Do you know what the bias currents through the circuit are? Typically you'd use a current source into a current mirror - like you've already got - to exactly define the bias current through the circuit.
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Md Munir Hasan

11/06/2020, 1:34 AM
If you want a square signal at the output, that means the circuit needs to operate at non linear region which simply means the input voltage swing needs to be larger. I think 1mV is way smaller than the transistor threshold voltage which is why it cannot compare between 0V and 1mV . Try larger voltage swing like 500mV.
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Shabarish Nayakanti

11/06/2020, 5:44 AM
actually biasing using Idc 30uA was also giving almost same output like this but with different swings
@Md Munir Hasan thanks I will try with larger input voltage also
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