follow-up questions of quadrature signal

[westpoint]

Hi folks,

I'd made some progress through last post but now I come up with a new idea. To achieve this, let computer produce a constant voltage, and let it be the input of my circuit. The outputs are expected to be Sin(V) and Cos(V). Note that these two outputs are just some number, so V becomes the phase of the two quadrature waveform.

The idea is, by changing the voltage, we can have get arbitary phase we want. Now if I change the voltage, I can change the phase simultaneously. The requirement for this circuit is low-noise. The voltage is around 20KHz

It looks like some lookup table. V--sin(V) and cos(V). Is there anyone can help me with this? Many thanks!


without wax

 

[Laplace]

In order for the computer to produce the control voltage, it is presumed that a D-A conversion will be necessary. Then for your circuit to read this control voltage as a relative phase for digital lookup, it is presumed that an A-D conversion will be necessary. Why design the system in this complicated fashion, (D-A-->A-D), when it could be a simpler (D-->D) direct control interface? Your circuit will also need a clock signal to control when the next table lookup occurs and when new values are latched into the sin() & cos() D-A converters. Where does that clock come from? the computer? Does the clock frequency need to vary in sync with some other signal? If so then you may need a phase-locked loop (PLL) to generate N clock pulses for every cycle of the signal. I don't have a clue how to estimate phase jitter from the D-A sampling parameters. Or if the quadrature signals are not generated from D-A table lookup, could they be generated from 20khz phase offset square waves that are low-pass filtered?