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VCA824: VCA824: constant phase at different gain

Sang Hoang
Prodigy 20 points
Part Number: VCA824

Hello,

I am working on a redesign, I want a variable gain amplifier that has the same phase with different gain. In the old system it was done using an opamp and a digital potentiometer, noninverting amplifier. But because I'm changing the gain, I am affecting the bandwidth of the circuit, so the phase could be different. Also the digital potentiometer has capacitance, which would make it an RC filter and when the resistance is changed the cut-off frequency of the RC filter also changes and would affect the phase.

So I wanted to replace this circuit with the VCA824, but I wanted to know if the phase is the same at different gain.

Or are my assumptions wrong and it is possible to make a variable gain amplifier out of an opamp without any change in phase?

Best regards,

Sang

  • 0
    Guru 48155 points

    Well you don't give a frequency range for constant group delay, but yes the VCA824 should do pretty well there the way it works. Essentially, you are generating a signal as a current in that Rg element and then either passing it on or throwing it away in the multiplier stage. Should be relatively constant AC performance over gain range. 

  • 0 in reply to Michael Steffes
    Prodigy 20 points

    The system I'm working on measures the time of flight of an acoustic signal. The signal frequency can be varied between 50 kHz to about 300 kHz. Because the system operates at a frequency of 400 MHz it can't measure a displacement less than 2.5 ns. So for a 50 kHz signal the maximum phase shift had to be less than 0,045 degrees over the whole gain range. Now I know I can use the VCA824 as a variable gain amplifier in my system.

    Thank you for replying and answering my question.

    Sang