Hi Mustafa,

Please correct me if I am wrong, but isn't the ADC itself categorised as mixed-signal ? (Regardless of the VCRO part, that is !).

-Sanjay

@Roy, You are right, but I doubted it because the ADC circuit consists of digital circuits. That's why I am asking if it's considered mixed-signal or a digital.

You are right, it's a mixed signal circuit.

thank you.

@Roy, pretty simple and sufficient definition of mixed-signal integrated circuits is given on Wikipedia (see link attached), also pointing out that ADC circuits are intrinsically considered as mixed-signal components. As many other specialized components, mixed-signal chips are developed in order to optimize price and/or performance of particular signal processing subsystem...

https://en.wikipedia.org/wiki/Mixed-signal_integrated_circuit

All signal processing circuits whose main operation involves both analog and digital signals can be considered as mixed-signal circuits. All ADCs and DACs, regardless on how they are implemented, surely belong to this category.

By contrast, substantially analog circuits, (e.g. opamps), with minor/inessential digital configuration signals and/or internal digital circuitry cannot be considered mixed-signal circuits. Similarly, digital circuits with some analog tuning are excluded from the definition.

The ADC is inherently of mixed-signal nature because it has analog inputs and digital outputs. Moreover, a ring VCO is not made with digital cells ONLY. You need, somewhere, a node in which you will apply a voltage in order to change the output frequency. This may be achieved with a current-starved inverter (which is not a digital block, as it has an analog input). If such an input does not exist, it is not a VCO. Similarly, if the frequency is controlled by a digital signal, it is again not a VCO, but a DCO (digitally controlled oscillator). So, there is no way around: an ADC (independently on its construction) is a mixed-signal circuit.