02-11-2012, 05:20 PM
MC1496, MC1496B Balanced Modulators/ Demodulators
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These devices were designed for use where the output voltage is a
product of an input voltage (signal) and a switching function (carrier).
Typical applications include suppressed carrier and amplitude
modulation, synchronous detection, FM detection, phase detection,
and chopper applications. See ON Semiconductor Application Note
AN531 for additional design information.
Features
• Excellent Carrier Suppression −65 dB typ @ 0.5 MHz
−50 dB typ @ 10 MHz
• Adjustable Gain and Signal Handling
• Balanced Inputs and Outputs
• High Common Mode Rejection −85 dB Typical
• This Device Contains 8 Active Transistors
• Pb−Free Package is Available
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.
OPERATIONS INFORMATION
The MC1496, a monolithic balanced modulator circuit, is
shown in Figure 23.
This circuit consists of an upper quad differential amplifier
driven by a standard differential amplifier with dual current
sources. The output collectors are cross−coupled so that
full−wave balanced multiplication of the two input voltages
occurs. That is, the output signal is a constant times the
product of the two input signals.
Mathematical analysis of linear ac signal multiplication
indicates that the output spectrum will consist of only the sum
and difference of the two input frequencies. Thus, the device
may be used as a balanced modulator, doubly balanced mixer,
product detector, frequency doubler, and other applications
requiring these particular output signal characteristics.
The lower differential amplifier has its emitters connected
to the package pins so that an external emitter resistance may
be used. Also, external load resistors are employed at the
device output.