Carrier Suppression
Carrier suppression is defined as the ratio of each
sideband output to carrier output for the carrier and signal
voltage levels specified.
Carrier suppression is very dependent on carrier input
level, as shown in Figure 22. A low value of the carrier does
not fully switch the upper switching devices, and results in
lower signal gain, hence lower carrier suppression. A higher
than optimum carrier level results in unnecessary device and
circuit carrier feedthrough, which again degenerates the
suppression figure. The MC1496 has been characterized
with a 60 mVrms sinewave carrier input signal. This level
provides optimum carrier suppression at carrier frequencies
in the vicinity of 500 kHz, and is generally recommended for
balanced modulator applications.
Carrier feedthrough is independent of signal level, VS.
Thus carrier suppression can be maximized by operating
with large signal levels. However, a linear operating mode
must be maintained in the signal−input transistor pair −or
harmonics of the modulating signal will be generated and
appear in the device output as spurious sidebands of the
suppressed carrier. This requirement places an upper limit
on input−signal amplitude (see Figure 20). Note also that an
optimum carrier level is recommended in Figure 22 for good
carrier suppression and minimum spurious sideband
generation
Carrier Suppression
Carrier suppression is defined as the ratio of each
sideband output to carrier output for the carrier and signal
voltage levels specified.
Carrier suppression is very dependent on carrier input
level, as shown in Figure 22. A low value of the carrier does
not fully switch the upper switching devices, and results in
lower signal gain, hence lower carrier suppression. A higher
than optimum carrier level results in unnecessary device and
circuit carrier feedthrough, which again degenerates the
suppression figure. The MC1496 has been characterized
with a 60 mVrms sinewave carrier input signal. This level
provides optimum carrier suppression at carrier frequencies
in the vicinity of 500 kHz, and is generally recommended for
balanced modulator applications.
Carrier feedthrough is independent of signal level, VS.
Thus carrier suppression can be maximized by operating
with large signal levels. However, a linear operating mode
must be maintained in the signal−input transistor pair −or
harmonics of the modulating signal will be generated and
appear in the device output as spurious sidebands of the
suppressed carrier. This requirement places an upper limit
on input−signal amplitude (see Figure 20). Note also that an
optimum carrier level is recommended in Figure 22 for good
carrier suppression and minimum spurious sideband
generation
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