Lyle and Artie,Obviously the OPA1632 is a good selection. For the optimal dynamic range you may need voltage gain if you want to take the signals directly from the QSD witout using the INA163 in between. The QSD can handle max. signal about 4 Vpp (1.414 Vrms = 5.229 dBu = 3.01 dBV). The PCM1804 can stand differential 5.0 Vpp and PCM4202 6.0 Vpp. Of course these are marginal gains, but it is good engineering practice to have some hardware buffering and filtering before the ADC.
See also "Applications Information" Figures 12 to 14 of the PCM4202 data sheet.
Happy soldering, Ahti OH2RZ----- Original Message ----- From: "Lyle Johnson" <kk7p@wavecable.com> To: <Artie@Lekstutis.com>; "Xylo-SDR Discussion" <xylo-sdr@lists.ae5k.us>
Sent: Tuesday, December 20, 2005 5:46 AM Subject: Re: [Xylo-SDR] A/D anti-aliasing filters
The circuit in the TI data sheet is a combination single-ended to differential converter, and a lowpass filter.Figure 44 is in deed a single-ended to differential converter, followed by a differential amp that has shaped characteristics which are used in conjunction with the ADC itself to derive the overall noise performance.More information is on the TI OPA1632 data sheet. See also app note "Gain Scaling and Audio Performance of the PCM1804", slea003.pdf dated May, 2002 for more information. It may be that you don;t need this for the QSD, but I suspect you'lllose a few dB in overall performance. On the other hand, you may not :-)Enjoy! Lyle KK7P