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I am designing a VCO-based ADC (the circuit is shown below) for sampling the audio signal. The design I refered to this post: Low frequency in this VCO design. But I instead of use it as a VCO only, I want to design an ADC leveraging its characteristic of generating square wave to design an ADC.

I have changed the chip to LT1056 which is a high-speed opamp and I see that I work really well at input frequencies smaller than 2kHz (the sampling rates are from 33kHz to 175kHz, the resolution is 6-bit). But the resolution will decrease significantly if the input frequency is larger than 2kHz.

I am wonder if this topology is still good enough to sample the input as audio frequency. I am thinking about changing the chip to a faster one with better slew rate.

Can anyone recommend me a way to solve this problem?

enter image description here

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  • \$\begingroup\$ What problem are you trying to solve? What are your expectations for this archaic method of digitization of an analogue signal? \$\endgroup\$ Commented Nov 16 at 10:34
  • \$\begingroup\$ Not really I want to solve any problems, it is my curiosity. I just start learning about VCO and just try to do a simple design of VCO. And a question came to my mind that if the VCO can be considered as an ADC modulator, or not? Then I just wonder the bandwidth of the input, can use any techniques to use for audio bandwidth, or not? \$\endgroup\$ Commented Nov 16 at 21:08
  • \$\begingroup\$ In your question you say this: Can anyone recommend me a way to solve this problem? <-- hence, I repeat, what problem are you trying to solve? \$\endgroup\$ Commented Nov 16 at 21:49
  • \$\begingroup\$ The problem is enhancing the input bandwidth. The circuit now can work at the bandwidth below 2kHz, but when it comes to audio frequency (up to 20kHz), it doesnt work well \$\endgroup\$ Commented Nov 17 at 4:27
  • \$\begingroup\$ Make your vco run times times higher in frequency. \$\endgroup\$ Commented Nov 17 at 9:46

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