Advertisement
95307-000-01 6/87
RET-041 Instructions
page 19
ensure that the filter ' s response falls accurately above 10kHz, and ±at NRSC specifications
are met
Measuring the frequency of these notches and their depth is the best way of diagnosing
problems with such filters, since problems with a given notch can be associated with a given
FDNR in most cases.
Because all parts of the filter interact, failures which cannot be cured merely by replac
ing opamps are best left to factory service, since special tight-tolerance, tight-temperature-
coefficient parts are used in certain places. The circuitry has been designed to be insensitive
to normal unit-to-unit variations in opamps.) See Appendix F in the 9100 A Operating Man
ual or Section 5 in the 9100B Operating Manual for information on how to obtain factory
service.
To avoid possible clipping, the signal is attenuated 5dB with voltage divider R24, R25 before
being applied to the filter. This gain is made up by IC5a to restore unity gain at low
frequencies.
All-pass delay corrector IC5b adds frequency-dependent delay to the first filter as necessary
to make its time delay more constant with frequency, thereby minimizing overshoot
Any residual overshoot is then clipped in IC6a, and then the signal is applied to second
10kHz filter IC6b, IC7a. The primary purpose of this second filter is to remove harmonics
caused by clipping in IC6a.
Fig. 7: Response of the First 10kHz Low-Pass Filter in the Passband
Advertisement
