Datasheet

LM13700
www.ti.com SNOSBW2E –NOVEMBER 1999–REVISED MARCH 2013
Figure 24. Equivalent VCA Input Circuit
Stereo Volume Control
The circuit of Figure 25 uses the excellent matching of the two LM13700 amplifiers to provide a Stereo Volume
Control with a typical channel-to-channel gain tracking of 0.3 dB. R
P
is provided to minimize the output offset
voltage and may be replaced with two 510Ω resistors in AC-coupled applications. For the component values
given, amplifier gain is derived for Figure 23 as being:
(8)
If V
C
is derived from a second signal source then the circuit becomes an amplitude modulator or two-quadrant
multiplier as shown in Figure 26, where:
(9)
The constant term in the above equation may be cancelled by feeding I
S
× I
D
R
C
/2(V− + 1.4V) into I
O
. The circuit
of Figure 27 adds R
M
to provide this current, resulting in a four-quadrant multiplier where R
C
is trimmed such that
V
O
= 0V for V
IN2
= 0V. R
M
also serves as the load resistor for I
O
.
Figure 25. Stereo Volume Control
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