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controlled from 10 Hz to 300 Hz in a 1, 3, 10 sequence by lines that have the same name
as the bandwidth they activate. When none of the lines is activated, the filter has a 1 kHz
bandwidth.
The filter has five poles which are almost identical. Only one is described in detail. Each pole
has a negative output impedance to compensate for the series resistance of the crystal, but it
is adjustable in only two poles.
4th Pole @I
The basis of the buffer amplifier is a complementary feedback pair including Q9 and &lo.
(See Figure 1.)
Figure 1. Complementary Feedback Pair, Simplified Schematic
The bias current through QlO is 0.7 V/1620 4 mA, and the total current through QlO plus
the gate voltage.
The circuit as shown in Figure 1 has no gain. R39, R36, and C26 are added (see schematic) so
this stage has a gain of:
- 1 5 v
S U P P L Y
R38
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