SSM-2120 Analog, SSM-2120 Datasheet - Page 3

• Manufacturer Part Number: SSM-2120
• Description: (SSM-2122) Dynamic Range Processors/Dual VCA
• Manufacturer: Analog

REV. C
VOLTAGE-CONTROLLED AMPLIFIERS
The two voltage-controlled amplifiers are full Class A current
in/current out devices with complementary dB/V gain control
ports. The control sensitivities are +6 mV/dB and –6 mV/dB. A
resistor divider (attenuator) is used to adapt the sensitivity of an
external control voltage to the range of the control port. It is
best to use 200
VCA INPUTS
The signal inputs behave as virtual grounds. The input current
compliance range is determined by the current into the reference
current pin.
REFERENCE PIN
The reference current determines the input and output current
compliance range of the VCAs. The current into the reference
pin is set by connecting a resistor to V+. The voltage at the
reference pin is about two volts above V– and the current will be
The current consumption of the VCAs will be directly pro-
portional to I
operate at lower current levels which will reduce the effective
dynamic range of the VCAs. With a 200 A reference current,
the input and output clip points will be 400 A. In general:
VCA OUTPUTS
The VCA outputs are designed to interface directly with the virtual
ground inputs of external operational amplifiers configured as
current-to-voltage converters. The outputs must operate at virtual
ground because of the output stage’s finite output impedance.
The power supplies and selected compliance range determines
the values of input and output resistors needed. As an example,
with 15 V supplies and 400 A maximum input and output
current, choose R
range of 14.4 V. Note that the signal path through the VCA
including the output current-to-voltage converter is noninverting.
REF
IN
which is nominally 200 A. The device will
or less for the attenuator resistor to ground.
I
REF
= R
INPUT 1
INPUT 2
OUT
I
[(V ) – ((V – ) 2 V )]
CLIP
= 36 k for an output compliance
= 2 I
+V
–V
+V
–V
R
C1
C1
C2
C2
REF
REF
CFT 1
CFT 2
SSM2122
OUTPUT 1
OUTPUT 2
Figure 1. SSM2120 Block Diagram
REC
REC
IN 1
IN 2
–3–
VCA PERFORMANCE
Figures 2a and 2b show the typical THD and noise performance
of the VCAs over 20 dB gain/attenuation. Full Class A operation
provides very low THD.
2V
2V
Figure 2. Typical THD and Noise Performance
b. VCA Noise vs. Gain (20 kHz Bandwidth)
0.003
–70
–80
–90
0.03
0.01
RECTIFIER
RECTIFIER
–20
–20
WAVE
WAVE
FULL
FULL
a. VCA THD Performance vs. Gain
(+10 dBV In/Out @ 1 kHz)
|I
|I
IN
IN
|
|
–10
LOG AV 1
LOG AV 2
–10
V+
V+
THRESH 1
THRESH 2
SSM2120/SSM2122
GAIN – dB
GAIN – dB
0
0
CON
CON
V–
V–
OUT 1
OUT 2
10
10
20
20