I have an acoustic project that self-calibrates every so often by playing white noise and doing some processing on it. My white noise source circuit is below. My plan is to direct the white noise through an analog switch (TS5A3359 or similar) along with either a pure tone output or grounding, so I can kill speaker output when it's not needed. However, I'm concerned that when I'm not using it, the noise is still being generated, but the output is basically floating.

My questions are:

  1. Is this even a concern when the WhiteNoise connection is floating? and,
  2. If so, how to best isolate/shield/protect/whatever this section of the circuit from the rest of the PCB?

circuit for white noise gen

  • 2
    \$\begingroup\$ You can't just power down the white noise circuit? \$\endgroup\$
    – DKNguyen
    Feb 26 '19 at 23:03
  • \$\begingroup\$ @Toor I'd go with the same, but it might make sense to not do that, to keep the active components at the same, loaded, operational point to get them to stabilize thermally to keep the noise power as constant as possible with this very limited means. \$\endgroup\$ Feb 26 '19 at 23:05
  • \$\begingroup\$ @Toor I thought about that. Unfortunately I've designed myself into a corner wrt the rest of the circuit and that might be prohibitive. This is designed to be almost entirely autonomous, which of course doesn't preclude automatically powering this section down (there is a microcontroller elsewhere in the circuit), but I'd love to avoid that sort of fiddling if I can. \$\endgroup\$
    – Ben S.
    Feb 26 '19 at 23:28
  • \$\begingroup\$ Don't forget decoupling on your ICs. \$\endgroup\$
    – DKNguyen
    Feb 26 '19 at 23:37
  • \$\begingroup\$ It should be fine driving a floating output as long as crosstalk is not a problem. Have you or are you able to test if crosstalk is a problem? ADC circuits sometimes use one or even two latches or D-flip flops to disconnect the ADC from the serial bus when it's not being talked to (rather than just disabling via chip select). It stops the switching noise on the bus finding it's way across the parasitic capacitances inside the chip. \$\endgroup\$
    – DKNguyen
    Feb 26 '19 at 23:39

The Analog switch can easily power down U21.

I did something similar in the 70's with a PRSG IC from National and a 3dB /oct Brown Noise filter and a Yamaha 1/2 Octave graphic equalizer with peak detectors. It had a 3 second sequence as I recall.


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