Part Number: PCM1798
Other Parts Discussed in Thread: OPA1612
hi expert,
i'm using PCM1798 to do some design. schematic as follows.
in my design, R1=R2=1.69k, thin film resistor.
C1=C2=100pf, NPO cap.
U1/U2 is OPA1612. power supply +/-11.5V.
and test in U1/U2 ouput. PCM1798 out+ has 1.69*4=6.76Vpp and THD about -120dbc. while out- THD only about-110dbc. mainly HD2 is worse .
i want to know why out- has worse THD compared to out+? any way to improve out- THD?
Hi,
the THD numbers you shared are quite good actually, even -110 dB (0.0003%) is exceeding what is quoted in the d/s
As for what is causing this difference. I would check for any noise on the supplies for the OPA1612. Also there may be some variation in your C1,C2 capacitors. perhaps C1 capacitance is changing slightly due to the applied voltage. you may try using a film capacitor for C1,C2 as they will be more resistant to capacitance changes.
Also if possible you can check the THD before the OPA1612 circuit, perhaps the THD difference is from the IC itself and your circuit is fine.
Regards,
Arthur
