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NON - VIDEO APPLICATIONS
The previous applications use the GT4122 as an overall unity
gain, non-inverting system. With this same configuration it is
possible to make a simple Amplitude Modulator. It is also
possible to configure either input stage as an inverting amplifier
Photograph 9. Envelope Waveform of A.M. Signal
An Amplitude Modulator circuit is shown in Figure 8 and
produces an output spectrum as shown in Figure 9. The
resulting envelope waveform is shown in Photograph 9. For
this application, a 1V peak to peak, 1 MHz carrier is applied to
the non-inverting B-INPUT.
A 3kHz, 1V peak to peak audio signal is applied to the
CONTROL input superimposed on a +0.5V DC bias. The bias
centres the CONTROL signal with respect to the 0.5V DC
REFERENCE voltage.
Modulation is achieved by varying the CONTROL signal at the
audio rate which in turn allows more or less of the carrier,
appearing on B-INPUT, through to the OUTPUT.
Post mixing of this signal would place the carrier on any
desired RF channel.
0
-20
-40
-60
-80
-100 -9k -6k -3k 1M 3k 6k 9k
FREQUENCY (Hz)
Fig. 9 Spectrum of A.M. Signal
RV1
1V P-P TRIANGLE
WAVE AT15 kHz
(V = 0 to 1V)
DC OFFSET = 0.5V
CONTROL
INPUT
A - IN
B - IN
STROBE
OUT
O/C
GND
1.0V
RV2
RV3
TO
SCOPE
CHOLD
Fig. 8 Amplitude Modulator Circuit
and produce anti-phase signals which are then applied to the
internal summing circuits. This allows the device to be used
as a Double Sideband Balanced Modulator. Both of these
applications are described below.
AMPLITUDE MODULATOR
G