T H AT
Corporation
Pre-Trimmed IC
Voltage Controlled Amplifiers
THAT
2180A, 2180B, 2180C
FEATURES
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Wide Dynamic Range: >120 dB
Wide Gain Range: >130 dB
Exponential (dB) Gain Control
Low Distortion: < 0.01 % (2180A)
Wide Gain-Bandwidth: 20 MHz
Dual Gain-Control Ports (pos/neg)
Pin-Compatible with 2150-Series
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APPLICATIONS
Faders
Panners
Compressors
Expanders
Equalizers
Filters
Oscillators
Automation System
Description
THAT 2180 Series integrated-circuit voltage con-
trolled amplifiers (VCAs) are very high-performance
current-in/current-out devices with two oppos-
ing-polarity, voltage-sensitive control ports. They offer
wide-range exponential control of gain and attenuation
with low signal distortion. The parts are trimmed at
wafer stage for low THD and control-voltage
feedthrough without further adjustment.
The VCA design takes advantage of a fully comple-
mentary dielectric isolation process which offers
closely matched NPN/PNP pairs, to deliver discrete
performance at IC prices. The parts are available in
three grades, selected for factory trimmed distortion,
alowing the user to optimize cost vs. performance. The
2180 Series is available in an 8-pin single-in-line (SIP)
package.
Pin Name
Input
7
SIP Pin
1
2
3
4
5
6
7
8
2k
Vcc
Ec+
Ec–
Sym
V–
Gnd
V+
Output
BIAS CURRENT
COMPENSATION
2
Ec+
25
Vbe
MULTI-
PLIER
Ec-
3
8
4
Input
1
6
Output
Sym
Iadj
5
Gnd
Table 1. 2180 Series Pin Assignments
Max THD @1 V,
1 kHz, 0 dB
0.01%
0.02%
0.05%
Plastic
SIP
2180LA
2180LB
2180LC
V-
Iset
Figure 1. 2180 Series Equivalent Circuit Diagram
Table 2. Ordering Information
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
Page 2
THAT2180 Series IC VCAs
SPECIFICATIONS
1
Absolute -Maximum Ratings (T
A
= 25°C)
Positive Supply Voltage (V
CC
)
Negative Supply Voltage (V
EE
)
Supply Current (I
CC
)
Max
DE
C
E
C+
- (E
C-
)
+20 V
-20 V
10 mA
±
1V
Power Dissipation (P
D
) (T
A
= 75°C)
Operating Temperature Range (T
OP
)
Storage Temperature Range (T
ST
)
330 mW
0 to +70°C
-40 to +125°C
Recommended Operating Conditions
2180A
Parameter
Positive Supply Voltage
Bias Current
Signal Current
Symbol
V
CC
I
SET
I
IN
+I
OUT
V
CC
- V
EE
= 30 V
I
SET
= 2.4mA
Conditions
Min
+4
-4
1
—
Typ
+15
-15
2.4
0.35
Max
+18
-18
5
1.5
Min
+4
-4
1
—
2180B
Typ
+15
-15
2.4
0.35
Max
+18
-18
5
1.5
Min
+4
-4
1
—
2180C
Typ
+15
-15
2.4
0.35
Max
+18
-18
5
1.5
Units
V
V
mA
mA
rms
Negative Supply Voltage V
EE
Electrical Characteristics²
2180A
Parameter
Supply Current
Symbol
I
CC
Conditions
No Signal
No Signal
No Signal
R
out
= 20 kW
0 dB gain
+15 dB gain
+30 dB gain
Gain Cell Idling Current I
IDLE
Gain-Control Constant
E
C+
/Gain (dB)
E
C-
/Gain (dB)
T
A
=25°C (T
CHIP
@35°C)
-60 dB < gain < +40 dB
Pin 2 (Fig. 14)
Pin 3
6.0
6.1
6.2
6.0
6.1
6.2
6.0
6.1
6.2
mV/dB
mV/dB
%/°C
%
dB
-6.2 -6.1 -6.0
— +0.33 —
—
110
0.5
115
2
—
-6.2 -6.1 -6.0
— +0.33 —
—
110
0.5
115
2
-6.2 -6.1 -6.0
— +0.33 —
—
110
0.5
115
2
—
—
—
—
—
0.5
1
3
20
1
3
12
—
—
—
—
—
1
1.5
5
20
2
4
15
—
—
—
—
—
1.5
3
9
20
3
10
30
—
mV
mV
mV
mA
Min
—
—
—
Typ
2.4
2
±5
Max
4
10
—
Min
—
—
—
2180B
Typ
2.4
2
±5
Max
4
12
—
Min
—
—
—
2180C
Typ
2.4
2
±5
Max
4
15
—
Units
mA
nA
mV
Equiv. Input Bias Current I
B
Input Offset Voltage
V
OFF(IN)
Output Offset Voltage V
OFF(OUT)
Gain-Control TempCo
DE
C
/
DT
CHIP
Ref T
CHIP
= 27°C
Gain-Control Linearity
1 kHz Off Isolation
Output Noise
e
n(OUT)
-60 to +40 dB gain
E
C+
= -360 mV, E
C-
= +360 mV
20 Hz ~ 20 kHz
R
out
= 20kW
0 dB gain
+15 dB gain
Voltage at V-
V
V-
No Signal
—
—
-98
-88
-97
-86
—
—
-98
-88
-96
-85
—
—
-98
-88
-95
-84
dBV
dBV
V
-3.1 -2.85 -2.6
-3.1 -2.85 -2.5
-3.1 -2.85 -2.6
1. All specifications subject to change without notice.
2. Unless otherwise noted, T
A
=25°C, V
CC
= +15V, V
EE
= –15V. Test circuit is as shown in Figure 2.
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
600029 Rev 01
Page 3
Electrical Characteristics (Cont'd.)
2180A
Parameter
Total Harmonic Distortion
Symbol
THD
Conditions
1 kHz, No External Trim
V
IN
= 0 dBV, 0 dB gain
V
IN
= +10 dBV, -15 dB gain
V
IN
= -5 dBV, +15 dB gain
Slew Rate
Gain at 0 V Control Voltage
R
in
= R
out
= 20 kW
E
C-
= 0 mV
—
—
—
—
-0.1
0.005 0.010
0.020 0.030
0.020 0.030
12
0.0
—
+0.1
—
—
—
—
0.010 0.020
0.030 0.040
0.030 0.040
12
—
+0.15
—
—
—
—
-0.2
0.030 0.050
0.040 0.070
0.040 0.070
12
0.0
—
+0.2
%
%
%
V/ms
dB
Min
Typ
Max
Min
2180B
Typ
Max
Min
2180C
Typ
Max
Units
-0.15 0.0
2180
Series
VCA
IN
10u
20k
1
Vcc
Ec-
3
Ec-
SYM
Ec+
22p
20k
OUT
8
7
V+
-IN
GND
V-
5
6
2
4
-
NC
+
OP275
OUT
Power Supplies
Vcc = +15 V
Vee = -15 V
5.1k
Vee
Figure 2. Typical Application Circuit
Figure 3. 2180 Series Frequency Response Vs. Gain
Figure 4. 2180 Series Noise (20kHz NBW) Vs. Gain
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
Page 4
THAT2180 Series IC VCAs
Theory of Operation
3
The THAT 2180 Series VCAs are designed for high
performance in audio-frequency applications requiring
exponential gain control, low distortion, wide dynamic
range and low control-voltage feedthrough. These parts
control gain by converting an input current signal to a
bipolar logged voltage, adding a dc control voltage, and
re-converting the summed voltage back to a current
through a bipolar antilog circuit.
Figure 5 presents a considerably simplified internal
circuit diagram of the IC. The ac input signal current
flows in pin1, the input pin. An internal operational
transconductance amplifier (OTA) works to maintain
pin 1 at a virtual ground potential by driving the emitters
of Q1 and (through the Voltage Bias Generator) Q3.
Q3/D3 and Q1/D1 act to log the input current, producing
a voltage, V3, which represents the bipolar logarithm of
the input current. (The voltage at the junction of D1 and
D2 is the same as V3, but shifted by four forward V
be
drops.)
Figure 6. Gain vs. Control Voltage (E
C+
, Pin 2) at 25°C
Gain Control
Since pin 8, the output, is usually connected to a vir-
tual ground, Q2/D2 and Q4/D4 take the bipolar antilog
of V3, creating an output current which is a precise rep-
lica of the input current. If pin 2 (Ec+) and pin 3 (Ec-)
are held at ground, the output current will equal the in-
put current. For pin 2 positive or pin 3 negative, the out-
put current will be scaled larger than the input current.
For pin 2 negative or pin 3 positive, the output current is
scaled smaller than the input.
The scale factor between the output and input cur-
rents is the gain of the VCA. Either pin 2 (Ec+) or pin 3
(Ec-), or both, may be used to control gain. Gain is expo-
nentially proportional to the voltage at pin 2, and expo-
Figure 7. Gain vs. Control Voltage (Ec-, Pin 3) at 25°C
+
D1
2
D2
Q2
Voltage
Bias
Generator
3
8
Figure 8. Gain vs. Control Voltage (Ec-) with Temp (°C)
nentially proportional to the negative of the voltage at
pin 3. Therefore, pin 2 (Ec+) is the
positive
control port,
while pin 3 (Ec-) is the
negative
control port. Because of
the exponential characteristic, the control voltage sets
gain
linearly
in
decibels.
Figure 6 shows the decibel cur-
rent gain of a 2180 versus the voltage at Ec+, while Fig-
ure 7 shows gain versus the Ec-.
Ec+
IN
1
Q1
Ec-
OUT
SYM
I
IN
25
Q3
Q4
4
D3
D4
Temperature Effects
Iadj
V
3
V-
5
Icell
Figure 5. Simplified Internal Circuit Diagram
The logging and antilogging in the VCA depends on
the logarithmic relationship between voltage and current
in a semiconductor junction (in particular, between a
transistor's V
be
and I
c
). As is well known, this relation-
ship is temperature dependent. Therefore, the gain of
any log-antilog VCA depends on its temperature.
3. For more details about the internal workings of the 2180 Series of VCAs, see
An Improved Monolithic Volt-
age-Controlled Amplifier,
by Gary K. Hebert (Vice-President, Engineering, for THAT Corporation), presented at the 99th
convention of the Audio Engineering Society, New York, Preprint number 4055.
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
600029 Rev 01
Page 5
Figure 8 shows the effect of temperature on the nega-
tive control port. (The positive control port behaves in the
same manner.) Note that the gain at Ec = 0 V is 0 dB, re-
gardless of temperature. Changing temperature changes
the
scale factor
of the gain by 0.33%/°C, which pivots the
curve about the 0 dB point.
Mathematically, the 2180's gain characteristic is
Gain
=
E
C
+
-
E
C
-
,
(0.0061)(1
+
0.0033DT)
Eq. 1
recommended. In particular, the 2180 maintains low
distortion over a wide range of gain, cut and signal lev-
els. Figures 10 through 12 show typical distortion per-
formance for representative samples of each grade of the
part. Figure 13 shows the harmonic content of the dis-
tortion in a typical B-grade part.
where
DT
is the difference between room temperature
(25°C) and the actual temperature, and Gain is the
gain in decibels. At room temperature, this reduces to
Gain
=
E
C
+
-
E
C
-
,
0.0061
E
C
+
,
0.0061
-
E
C
-
,
0.0061
Eq. 2
If only the positive control port is used, this becomes
Gain
=
Eq. 3
Figure 10. 1 kHz THD+Noise Vs. Input Level, 0 dB Gain
If only the negative control port is used, this becomes
Gain
=
Eq. 4
DC Bias Currents
The 2180 current consumption is determined by the
resistor between pin 5 (V-) and the negative supply voltage
(V
EE
). Typically, with 15V supplies, the resistor is 5.1 kW,
which provides approximately 2.4 mA. This current is
split into two paths: 570
mA
is used for biasing the IC,
and the remainder becomes Icell as shown in Figure 5.
Icell is further split in two parts: about 20
mA
biases the
core transistors (Q1 through Q4), the rest is available for
input and output signal current
Figure 11. 1 kHz THD+Noise Vs. Input Level,
+15 dB Gain
DC Feedthrough
Normally, a small dc error term flows in pin 8 (the
output). When the gain is changed, the dc term changes.
This control-voltage feedthrough is more pronounced
with gain; the –A version of the part produces the least
feedthrough, the –C version the most. See Figure 9 for
typical curves for dc offset vs. gain
Audio Performance
The 2180-Series VCA design, fabrication and testing
ensure extremely good audio performance when used as
Figure 12. 1 kHz THD+Noise Vs. Input Level,
-15 dB Gain
Figure 9. Representative DC Offset Vs. Gain
Figure 13. FFT of THD, 0dB gain, 1kHz, 0dBV,
Typical 2180B
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
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