Resonance Control Voltage Rejection; Stage Buffers - Sequential Pro One Technical Manual

ICR
( P A )
FIGURE
6: TRANSCONDUCTANCE V.S. CONTROL CUBAEnlT OF
RESONANCE C E L L
200K
FIGURE
8: ZERO REFERENCING THE INPUT AN0 OUTPUT
and
These components are
shown in the filter circuits of
Figures 2-5. To obtain minimum
control voltage feedthrough,
the
best technique for adjusting this
trim is to switch back and forth
between the maximum and
minimum control voltages while
adjusting
the
pot so
that the
D.C.
output voltage at these two
extreme conditions is the same.
Resonance Control
Voltage Rejection
For most applications, no trim-
ming should be necessary.
However, i f required, the reso-
nance control voltage feed-
through may be minimized by
applying a small D.C. voltage on
the resonance signal input pin,
pin 8 . d typical set-up is shown
in Figure
7.
The value of
R R T
should
be selected so
the trim
pot i s able t o adjust the voltage
on pin
8
by
f 3QmV.
Stage Buffers
may begin t o degrade the per-
formance of the filter,
especially
i f the loads on each buffer
differ by more than this amount.
The
maximum recommended
D.C. loads are
tmA
source.
251)uA sink, and a 150yA load
difference between buffers.
The
maximum recommended
A.C. loads are f250pA.
Since the D.C. level a t the
filter output is a t some non-
zero voltage
(6.9
volts for
Vcc = +15V), a coupling
capacitor
will
be required
somewhere in the signal chain,
either a t the filter output or
the following device inputs.
Note that if
the
resonance
feature i s being used, the filter
output i s already D.C. blocked
by
the resonance input
coupling capacitor, thus pro-
viding a convenient output
point. If D.C. coupling t a
ground referenced inputs and
outputs is required,
t h e
schemes
shown in Figure 8 may be used.
Note that the output circuit
has the benefits of 1 ) allowing
far
gain
after the filter, and
2 ) providing an output with
greater drive capability. The
buffer
outputs are not short
Each buffer can source up to circuit protected; therefore
lOmA and sink a nominal
care should be exercised t o
SOOpA. However, any D.C.
laad
not short the outputs to ground
greater than +200pA to +300uA
or either supply.
h
2900 Mauricia Ave.
Santa Clara, CA
95051
(408)247-8046
Covered b y U.S. Patent g4,004,141. Curtis Electromusic Specialties (CESI
assumes no respons~btl~ty for use of any c ~ r c u ~ t v descrrbed. No clrcult lrcenses
are impl~ed. CES reserves the right. at any
rime
without notice, to change,sa!d
circu~try.
Printed W.S.A. C 3 1980
6