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PCM1794 vs PCM1793 balanced output?
PCM1794 vs PCM1793 balanced output?
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Old 15th January 2020, 04:47 PM   #11
abza is offline abza  South Africa
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Join Date: May 2014
Aha, interesting - I wasn't aware this could be achieved passively. That's pretty appealing, if anything just for the lower component count! So a simple resistor to ground is all that's needed to convert current to voltage?

Here's what I have as a quick mockup of that, including your idea to fold the shunt resistor into acting as some low pass filtering:

Click the image to open in full size.

C1: DC blocking cap, and part of the high pass filter together with R1.

R1: I/V resistor. Is this layout correct?

C2: Initial LP filtering

R2: Low pass filter with C3, as well as gain control with RFB.
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Old 15th January 2020, 08:04 PM   #12
Ken Newton is offline Ken Newton  United States
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Join Date: Apr 2003
Location: Eastern Pennsylvania
The C1 blocking cap. MUST be located somewhere AFTER the I/V resistor R1. This is because the PCM1794A needs to pass a 6.2mA D.C. bias current from each output pin to ground, which it does here via R1. As shown, C1 would block passage of this necessary current. I would locate C1 as suggested earlier, between the 2nd filter pole and the output amplifier. I suggest this so that the C1 doesn't have to pass the full-band DAC output signal. Also, R2, C3 values should be chosen with the values of R1, C2 in mind, so that the in-band response remains flat to 20kHz.
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