MC1496, MC1496B
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9
Table 1. Voltage Gain and Output Frequencies
Carrier Input Signal (V
C
) Approximate Voltage Gain Output Signal Frequency(s)
Low−level dc
R
L
V
C
2(R
E
) 2r
e
)
ǒ
KT
q
Ǔ
f
M
High−level dc
R
L
R
E
) 2r
e
f
M
Low−level ac
R
L
V
C
(rms)
22
Ǹ
ǒ
KT
q
Ǔ
(R
E
) 2r
e
)
f
C
±f
M
High−level ac
0.637 R
L
R
E
) 2r
e
f
C
±f
M
, 3f
C
±f
M
, 5f
C
±f
M
, . . .
2. Low−level Modulating Signal, V
M
, assumed in all cases. V
C
is Carrier Input Voltage.
3. When the output signal contains multiple frequencies, the gain expression given is for the output amplitude ofeach of the two desired outputs,
f
C
+ f
M
and f
C
− f
M
.
4. All gain expressions are for a single−ended output. For a differential output connection, multiply each expression by two.
5. R
L
= Load resistance.
6. R
E
= Emitter resistance between Pins 2 and 3.
7. r
e
= Transistor dynamic emitter resistance, at 25°C;
re [
26 mV
I
5
(mA)
8. K = Boltzmann′s Constant, T = temperature in degrees Kelvin, q = the charge on an electron.
The gain from the modulating signal input port to the
output is the MC1496 gain parameter which is most often of
interest to the designer. This gain has significance only when
the lower differential amplifier is operated in a linear mode,
but this includes most applications of the device.
As previously mentioned, the upper quad differential
amplifier may be operated either in a linear or a saturated
mode. Approximate gain expressions have been developed
for the MC1496 for a low−level modulating signal input and
the following carrier input conditions:
1) Low−level dc
2) High−level dc
3) Low−level ac
4) High−level ac
These gains are summarized in Table 1, along with the
frequency components contained in the output signal.
APPLICATIONS INFORMATION
Double sideband suppressed carrier modulation is the
basic application of the MC1496. The suggested circuit for
this application is shown on the front page of this data sheet.
In some applications, it may be necessary to operate the
MC1496 with a single dc supply voltage instead of dual
supplies. Figure 25 shows a balanced modulator designed
for operation with a single 12 Vdc supply. Performance of
this circuit is similar to that of the dual supply modulator.
AM Modulator
The circuit shown in Figure 26 may be used as an
amplitude modulator with a minor modification.
All that is required to shift from suppressed carrier to AM
operation is to adjust the carrier null potentiometer for the
proper amount of carrier insertion in the output signal.
However, the suppressed carrier null circuitry as shown in
Figure 26 does not have sufficient adjustment range.
Therefore, the modulator may be modified for AM
operation by changing two resistor values in the null circuit
as shown in Figure 27.
Product Detector
The MC1496 makes an excellent SSB product detector
(see Figure 28).
This product detector has a sensitivity of 3.0 V and a
dynamic range of 90 dB when operating at an intermediate
frequency of 9.0 MHz.
The detector is broadband for the entire high frequency
range. For operation at very low intermediate frequencies
down to 50 kHz the 0.1 F capacitors on Pins 8 and 10 should
be increased to 1.0 F. Also, the output filter at Pin 12 can
be tailored to a specific intermediate frequency and audio
amplifier input impedance.
As in all applications of the MC1496, the emitter
resistance between Pins 2 and 3 may be increased or
decreased to adjust circuit gain, sensitivity, and dynamic
range.
This circuit may also be used as an AM detector by
introducing carrier signal at the carrier input and an AM
signal at the SSB input.
The carrier signal may be derived from the intermediate
frequency signal or generated locally. The carrier signal may
