EL4450C
Wideband Four-Quadrant Multiplier
about 37 dB worst-case. Better suppression can be
obtained by nulling the offset of the X input. Similarly,
nulling the offset of the Y input will improve signal-port
suppression. Driving an input differentially will also
maximize feedthrough suppression at frequencies
beyond 10 MHz.
Mixer Applications
Because of its lower distortion levels, the Y input is the
better choice for a mixer’s signal port. The X input
would receive oscillator amplitudes of about 1V RMS
maximum. Carrier suppression is initially limited by the
offset voltage of the Y input, 20 mV maximum, and is
AC Level Detectors
Square-law converters are commonly used to convert
AC signals to DC voltages corresponding to the original
amplitude in subsystems like automatic gain controls
(AGC’s) and amplitude-stabilized oscillators. Due to the
controlled AC amplitudes, the inputs of the multiplier
will see a relatively constant signal level. Best perfor-
mance will be obtained for inputs between 200 mVRMS
and 1 VRMS. The traditional use of the EL4450C as an
AGC detector and control loop would be:
Figure 2. Traditional AGC Detector/DC Feedback Circuit
The EL4450C simply provides an output equal to the
square of the input signal and an integrator filters out the
AC component, while comparing the DC component to
an amplitude reference. The integrator output is the DC
control voltage to the variable-gain sections of the AGC
(not shown). If a negative polarity of reference is
required, one of the multiplier input terminal pairs is
reversed, inverting the multiplier output. In-
put bias current will cause input voltage offsets due to
source impedances; putting a compensating resistor in
series with the grounded inputs of the EL4450C will
reduce this offset greatly.
This control system will attempt to force
VIN,RMS2/4=VREF
.
The extra op-amp can be eliminated by using this circuit:
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ELANTEC [ ELANTEC SEMICONDUCTOR ]
