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follow-up questions of quadrature signal

westpoint

Feb 19, 2012
5
Joined
Feb 19, 2012
Messages
5
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

Apr 4, 2010
1,252
Joined
Apr 4, 2010
Messages
1,252
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?
 
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