(updated 9-26-7)
This jumper programmable instrumentation amplifier uses 0.02% 10k and 20k resistors. It includes a 100_Ohm trim pot for common mode reject trim, and a 50k offset pot to calibrate the offset of the PP85A. Two useful gains are 1x and 0.5x. The 0.5x gain is useful to take the difference between two full scale +/-10V signals and end up with a +/-10V full scale output.
I made a few measurements of the SPDIF before returning it to Dan Sheingold. These measurements were made in March 2006, but uploaded in September of 2007. These measurements were made without touching the external offset and gain measurements. The external CMRR adjustment was designed to achieve best CMRR at the possible expense of some gain error.
-I measured for the non-inverting input: small signal bandwidth is 2.1MHz, the slew rate is 1V/us, Full power bandwidth is 36kHz with 20Vp-p.
-Measured DC offset is 30uV with pins 6,7,12 grounded. Maximum DC swing was +/-13.3V
-Measured DC Common Mode Rejection Ratio (CMRR) with a gain of 1 was 108dB from a common mode swing of 26Vp-p. This is only 100uV p-p of common mode rejection error. At gain of 0.5 the rejection was slightly worse at 102dB, or 200uVp-p.
-The transfer function from each input showed only small errors as follows:
|
+input at pin 6 |
output at pin 1 |
output error measured directly |
|
10V |
9.9994V |
-506uV |
|
5V |
4.9998V |
-247uV |
|
0V |
0.0001V |
+20uV |
|
-5V |
-4.9997V |
+300uV |
|
-10V |
-9.9995V |
+540uV |
|
-input at pin 7 |
output at pin 1 |
output error calculated from absolute measurement |
|
10V |
-9.9989V |
+1100uV |
|
5V |
-4.9991V |
+900uV |
|
0V |
0.0002V |
+200uV |
|
-5V |
5.0003V |
+300uV |
|
-10V |
10.0001V |
+100uV |
These very good measurements on a 40 year old module show that beyond the quality of the opamp design, the quality and stability of the resistors kept this OPAMP very accurate for several decades. These measurements were all done without touching the external CMRR and OFFSET trim pots. One measure of stability may have been confered by the conformal coating (perhaps Humiseal), as can be seen in the photos below. As I remember from my days of ADC modular design in the 1980's at Analogic, the choise of discrete precision resistors was a pretty serious matter.
The data sheets for the two potted modules OPAMP PP85A and unity gain booster PP66A are in this archive.
This module was not widely commercialized, so a data sheet may not have been produced.
