Electrical – Why is resistor needed in ADC circuit

adcvoltage

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This figure shows an ADC.

My question: Why there is resistor (R) connecting to inverting pin of each OPAMP.

Are they really necessary? In my opinion, they can be removed because you will have to compare the
voltage at non-inverting pin to the voltage at inverting pin anyway. And that is enough for converting
analog Vin to digital signal.

So what's the point for having those resistors?

Best Answer

In my opinion, they can be removed because you will have to compare the voltage at non-inverting pin to the voltage at inverting pin anyway.

You have to have a voltage to compare with.

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Figure 1. Apply 8 V to the Vref input and each of the comparators gets a proportional voltage.

In this case we've applied 8 V and there are seven steps so each comparator has a reference voltage between 1 and 7 volts.

So what's the point for having those resistors?

It's to generate the reference voltages.

  • Now if Vin < 1 V all comparators will be off.
  • When 1 V ≤ Vin < 2 V comparator 'a' will turn on.
  • When 2 V ≤ Vin < 3 V comparators 'a' and 'b' will turn on.
  • etc.
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