MC1496_06 Datasheet, PDF (8/14 Pages) ON Semiconductor – Balanced Modulators/Demodulators

MC1496, MC1496B
0
10
20
3f_C ± f_S
30
40
2f_C ± f_S
50
2f_C ± 2f_S
60
70
0.05 0.1
0.5 1.0
5.0 10
50
f_C, CARRIER FREQUENCY (MHz)
Figure 21. Suppression of Carrier Harmonic
Sidebands versus Carrier Frequency
0
10
20
30
f_C = 10 MHz
40
50
f_C = 500 kHz
60
70
0
100
200
300
400
500
V_C, CARRIER INPUT LEVEL (mVrms)
Figure 22. Carrier Suppression versus
Carrier Input Level
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.
Signal Levels
The upper quad differential amplifier may be operated
either in a linear or a saturated mode. The lower differential
amplifier is operated in a linear mode for most applications.
For low−level operation at both input ports, the output
signal will contain sum and difference frequency
(−) 12
V_o,
(+) 6 ^Output
10 (−)
Carrier
Input
V_C
8
(+)
4 (−)
Signal
Input
V_{S 1 (+)}
2
Gain
3 ^Adjust
Bias 5
(Pin numbers
500 500
500 per G package)
V_EE 14
Figure 23. Circuit Schematic
components and have an amplitude which is a function of the
product of the input signal amplitudes.
For high−level operation at the carrier input port and
linear operation at the modulating signal port, the output
signal will contain sum and difference frequency
components of the modulating signal frequency and the
fundamental and odd harmonics of the carrier frequency.
The output amplitude will be a constant times the
modulating signal amplitude. Any amplitude variations in
the carrier signal will not appear in the output.
The linear signal handling capabilities of a differential
amplifier are well defined. With no emitter degeneration, the
maximum input voltage for linear operation is
approximately 25 mV peak. Since the upper differential
amplifier has its emitters internally connected, this voltage
applies to the carrier input port for all conditions.
Since the lower differential amplifier has provisions for an
external emitter resistance, its linear signal handling range
may be adjusted by the user. The maximum input voltage for
linear operation may be approximated from the following
expression:
V = (I5) (R_E) volts peak.
This expression may be used to compute the minimum
value of R_E for a given input voltage amplitude.
1.0 k
1.0 k
51
CarrierV^{C 0.1 mF}
Input
V_S
Modulating
Signal _{10 k 10 k}
Input
50 k
0.1 mF
2
8
10
1
4
51 51
R_e 1.0 k
MC1496
14
3
R_L
3.9 k
6
12
5
I5 _{6.8 k}
Carrier Null
−8.0 Vdc
V_EE
Figure 24. Typical Modulator Circuit
12 Vdc
R_L
3.9 k
+V_o
−V_o
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