Alex_M wrote on Sun, 01 October 2006 06:51 |
I look for schema of Apogee AD-500 A/D converter. What chipset is used? Also interesting input LPF and buffer with good CMRR at high freq. AD-500 common mode rejection is: better than 90dB at 100Hz better than 70dB at 10kHz New delta-sigma hardware become worse in this parameter. |
danlavry wrote on Tue, 03 October 2006 14:24 |
In my view, one needs a lot more rejection at line frequency then it does at say 10KHz. Why? Because one can have an audio cable leading to an AD input run in parallel (and not too far) to an AC line, carrying a lot of power (relatively speaking) thus pick up a lot of common mode signal. As a rule, I can not think of "everyday case" where your AD input cable will be running in parallel to a cable with 110V (or 220V) with say some .1A (or 5A) at 10KHz. |
Alex_M wrote on Mon, 09 October 2006 01:02 | ||
I'm think about 30...300 kHz band (switching power sources). Single ended A/D chip in Apogee is PCM1750? Can You tell, how to improve CMRR performance of differential-input ADC chips (i.e. AK5394, AD7690) up to 90 dB in audio band? Convert balanced input to unbalanced and back to differential? |
abirkett wrote on Mon, 20 November 2006 14:24 |
I would firtsly try and track down the offending switching supplies and tame their EMC. Common mode chokes at the input often help, especially if followed by small caps to ground from the signal pair. If this is fails, then you can make a line receiver from an AD8130/AD8129 which has a CMRR of well over 100db@100kHz. I have used these devices to great effect in video systems. See AD8129/30 datasheet: http://www.analog.com/UploadedFiles/Data_Sheets/AD8129_8130. pdf Choose Zi and Zo to suit your needs. DC offset is less than 5mV and can be trimmed by lifting U2s + terminal and injecting an offset voltage. |