SSM2018TP View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
SSM2018TP Datasheet PDF : 16 Pages
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50pF
18k
V+
VIN+
VIN–
1µF 18k
1µF 18k
1
16
2
15
3
14
4 SSM2018T 13
5
12
6
11
7
10
8
9
47pF
V+
V+
100k
OP176
100k
10µF
VOUT
RB
1µF
V+
3k
1k
VCONTROL
SSM2018T/SSM2118T
Next the control feedthrough trim is done as follows:
1. Ground the input signal port and apply a 60 Hz sine wave
to the control port. The sine wave should have its high and
low peaks correspond to the highest gain to be used in the
application and 30 dB of attenuation, respectively. For ex-
ample, a range of +20 dB gain to 30 dB attenuation requires
that the sine wave amplitude ranges between –560 mV and
+840 mV on Pin 11.
2. Adjust the control feedthrough potentiometer to null the sig-
nal seen at the output.
VC
VG
VIN
V1–G
Figure 45. Single Supply Operation of SSM2018T
Operational Voltage Controlled Element
The SSM2018T has considerable flexibility beyond the basic
VCA circuit utilized throughout this data sheet. The name
“Operational Voltage Controlled Element” comes from the fact
that the part behaves much like an operational amplifier with a
second voltage controlled output. The symbol for the OVCE
connected as a unity gain follower/VCA is shown in Figure 46.
The voltage output labeled V1–G is fed back to the inverting in-
put just as for an op amp’s feedback. The VG output is ampli-
fied or attenuated depending upon the control voltage. Because
the OVCE works just like an op amp, the feedback could just as
easily have included resistors to add gain, or a filter network to
add frequency shaping. The full circuit for the OVCE is shown
in Figure 47. Notice that the amplifier whose output (Pin 16)
was originally connected to VMINUS is now the output for feed-
back. As mentioned before, because the SSM2018T is trimmed
for the basic VCA configuration, potentiometers are needed for
the OVCE configuration to ensure the best THD and control
feedthrough performance.
If a symmetry trim is to be performed, it should precede the
control feedthrough trim and be done as follows:
1. Apply a 1 kHz sine wave of +10 dBu to the input, with the
control voltage set for unity gain.
2. Adjust the symmetry trim potentiometer to minimize distor-
tion of the output signal.
Figure 46. OVCE Follower/VCA Connection
V+
100kΩ
CONTROL
FEEDTHROUGH
TRIM
10MΩ
500kΩ
V–
50pF
18kΩ
SYMMETRY
TRIM
50pF
470kΩ
V1–G
18kΩ
VG
1
16
V+ 2
15
3
14
INPUTS
4 SSM2018T 13
5
12
6
11
7
10
RB
V+
3kΩ
1µF
V–
1kΩ
VCONTROL
8
9 NC
220pF
RB: 30kΩ FOR CLASS A
150kΩ FOR CLASS AB
NC = NO CONNECT
Figure 47. OVCE Application Circuit
REV. A
–15–
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