BSS THAT-2181 Datasheet

Blackmer® Trimmable IC

V

A

oltage Controlled Amplifiers

THAT 2181A, 2181B, 2181C

FEATURES

• Wide Dynamic Range: >120 dB

• Wide Gain Range: >130 dB

• Exponential (dB) Gain Control

• Low Distortion:
~ 0.0025 % (typical 2181A)
~ 0.005 % (typical 2181C)

• Wide Gain-Bandwidth: 20 MHz

• Dual Gain-Control Ports (pos/neg)

• Pin-Compatible with 2150-Series

Description

THAT 2181 Series integrated-circuit voltage
controlled amplifiers (VCAs) are very high­performance current-in/current-out devices with
two opposing-polarity, voltage-sensitive control
ports. They offer wide-range exponential control
of gain and attenuation with low signal distortion.
The parts are selected after packaging based
primarily on after-trim THD and control-voltage
feedthrough performance.

APPLICATIONS

• Faders

• Panners

• Compressors

• Expanders

• Equalizers

• Filters

• Oscillators

• Automation Systems

The VCA design takes advantage of a fully
complementary dielectric isolation process which
offers closely matched NPN/PNP pairs. This deliv­ers performance unobtainable through any
conventional process, integrated or discrete. The
parts are available in three grades, allowing the
user to optimize cost vs. performance. Both 8-pin
single-in-line (SIP) and surface mount (SO)
packages are available.

BIAS CURRENT

COMPENSATION

Input

1
6

Gnd

7

Iset

25

Output

Vcc

2

Ec+
Ec-

3

8

4

Sym

V-

5

Max Trimmed

@1V,1kHz,0dB

2k

Vbe

MULTI-

PLIER

Iadj

Figure 1. 2181 Series Equivalent Circuit Diagram

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; US

Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com

Copyright © 2008, THAT Corporation Document 600030 Rev 02

Table 1. Pin Assignments

THD

Table 2. Ordering information

Plastic

SIP

SO PinSIP PinPin Name

11Input
22Ec+
33Ec­44Sym
55V­66Gnd
77V+
88Output

Plastic

SO

2181AS08-U2181AL08-U0.01%
2181BS08-U2181BL08-U0.02%
2181CS08-U2181CL08-U0.05%

Document 600030 Rev 02 Page 2 of 12 THAT 2181 Series

Blackmer® Trimmable IC VCAs

SPECIFICATIONS

Absolute Maximum Ratings

Positive Supply Voltage (VCC)+20 V
Negative Supply Voltage (V
Supply Current (I
Maximum ∆E

) 10 mA

CC

EC+ - (EC-) ± 1 V

C

) -20 V

EE

Power Dissipation (P
Operating Temperature Range (T
Storage Temperature Range (T

1

2,3

) (TA = 75 ºC) 330 mW

D

) 0 to +70 ºC

OP

) -40 to +125 ºC

ST

Recommended Operating Conditions

2181A 2181B 2181C

Parameter Symbol Conditions Min Typ Max Min Typ Max Min Typ Max Units
Positive Supply Voltage V

Negative Supply Voltage V
Bias Current I
Signal Current I

CC

EE

SET

+ I

IN

OUT

VCC - VEE = 30 V 1 2.4 3.5 1 2.4 3.5 1 2.4 3.5 mA

I

= 2.4 mA — 0.35 2.5 — 0.35 2.5 — 0.35 2.5 mA

SET

Electrical Characteristics

Parameter Symbol Conditions Min Typ Max Min Typ Max Min Typ Max Units

+4 +15 +18 +4 +15 +18 +4 +15 +18 V

-4 -15 -18 -4 -15 -18 -4 -15 -18 V

2

2181A 2181B 2181C

Supply Current I
Equiv. Input Bias Current I
Input Offset Voltage V
Output Offset Voltage V

CC

B

OFF(IN)

OFF(OUT)

No signal — 2.4 4 — 2.4 4 — 2.4 4 mA
No Signal — 2 10 — 2 12 — 2 15 nA
No Signal — ±5 — — ±5 — — ±5 — mV

R

= 20 kΩ

out

0 dB gain — 0.5 1 — 1 2 — 1.5 3 mV
+15 dB gain — 1 3 — 1.5 4 — 3 10 mV
+30 dB gain — 3 12 — 5 15 — 9 30 mV

Gain Cell Idling Current I

IDLE

Gain-Control Constant TA =25°C (T

CHIP

≅35°C)

—20 — —20 — —20 — µA

-60 dB < gain < +40 dB

/Gain (dB) Pin 2 (Fig. 15) 6.0 6.1 6.2 6.0 6.1 6.2 6.0 6.1 6.2 mV/dB

E

C+

/Gain (dB) Pin 3 -6.2 -6.1 -6.0 -6.2 -6.1 -6.0 -6.2 -6.1 -6.0 mV/dB

E

C-

Gain-Control TempCo ∆EC /∆T

CHIP

Ref T

= 27°C — +0.33 — — +0.33 — — +0.33 — %/°C

CHIP

Gain-Control Linearity -60 to +40 dB gain — 0.5 2 — 0.5 2 — 0.5 2 %
1 kHz Off Isolation EC+= -360mV,EC-=+360mV 110 115 — 110 115 — 110 115 — dB
Output Noise e

n(OUT)

20 Hz ~ 20 kHz

= 20kΩ

R

out

0 dB gain — -98 -97 — -98 -96 — -98 -95 dBV
+15 dB gain — -88 -86 — -88 -85 — -88 -84 dBV

Voltage at V- V

V-

No Signal -3.1 -2.85 -2.6 -3.1 -2.85 -2.6 -3.2 -2.85 -2.6 V

1. All specifications are subject to change without notice.

2. Unless otherwise noted, T

3. Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only; the functional operation of
the device at these or any other conditions above those indicated in the operational sections of this specification is not impli ed. Exposure to absolute maximum rating condi­tions for extended periods may affect device reliability.

=25ºC, VCC=+15V, VEE= -15V. Test circuit as shown in Figure 2. SYM ADJ is adjusted for minimum THD at 1 V, 1 kHz, Ec- = -Ec+ = 0 V.

A

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com

Copyright © 2008, THAT Corporation

THAT 2181 Series Page 3 of 12 Document 600030 Rev 02
Blackmer® Trimmable IC VCAs

Electrical Characteristics (con’t)

2181A 2181B 2181C

Parameter Symbol Conditions Min Typ Max Min Typ Max Min Typ Max Units
Total Harmonic Distortion THD 1 kHz

V

= 0 dBV, 0 dB gain — 0.0025 0.005 — 0.004 0.008 — 0.005 0.02 %

IN

V

= +10 dBV, -15 dB gain — 0.018 0.025 — 0.025 0.035 — 0.035 0.07 %

IN

= -5 dBV, +15 dB gain — 0.018 0.025 — 0.025 0.035 — 0.035 0.07 %

V

IN

V

= +10 dBV, 0 dB gain — 0.004 0.008 — 0.006 0.010 — 0.015 — %

IN

Slew Rate RIN = R
Symmetry Control Voltage V
Gain at 0 V Control Voltage EC- = 0 mV -0.1 0.0 +0.1 -0.15 0.0 +0.15 -0.2 0.0 +0.2 dB

= 0dB, Minimum THD -0.5 — +0.5 -1.5 — +1.5 -2.5 — +2.5 mV

SYMAV

= 20 kΩ —12 — —12 — —12 —V/µs

OUT

2

Vcc

2181

Ec-

22p

Series

7

3

V+

-IN

V-

GND

5

Ec­Ec+

6

1

SYM

2

4

OUT
8

20k

-

OP275

+

OUT

IN

10u

VCA

20k

Power Supplies

Vcc = +15 V

Vee = -15 V

5.1k
680k (2181A)

220k (2181B)
130k (2181C)

Vee

Figure 2. Typical Application Circuit

Rsym

50k

Vcc

SYM

ADJ

Vee

Figure 3. 2181 Series Frequency Response vs. Gain Figure 4. 2181 Series Noise (20kHz NBW) vs. Gain

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com

Copyright © 2008, THAT Corporation

Document 600030 Rev 02 Page 4 of 12 THAT 2181 Series

A

A

.

Blackmer® Trimmable IC VCAs

Theory of Operation

The THAT 2181 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 pin 1, 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

Gain Control

Since pin 8, the output, is usually connected to a
virtual ground, Q2/D2 and Q4/D4 take the bipolar
antilog of V3, creating an output current which is a
precise replica of the input current. If pin 2 (E
pin 3 (E
connected to a high impedance current source), the
output current will equal the input current. For pin 2
positive or pin 3 negative, the output 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.

) are held at ground (with pin 4 - SYM -

C-

drops.)

be

C+

) and

4

Figure 6. Gain vs. Control Voltage (EC+, Pin 2) at 25°C

Figure 7. Gain vs. Control Voltage (EC-, Pin 3) at 25°C

Figure 8. Gain vs. Control Voltage (E

) with Temp (°C)

C-

In normal operation, the output current is
converted to a voltage via an opamp-based I-V
converter, as shown in Figure 2, where the conver­sion ratio is determined by the feedback resistor
connected between the output and inverting input.
The signal path through the VCA and the output
opamp is non-inverting.

The scale factor between the output and input
currents is the gain of the VCA. Either pin 2 (Ec+) or
pin 3 (Ec-), or both, may be used to control gain.
Gain is exponentially proportional to the voltage at
pin 2, and exponentially proportional to the negative
of the voltage at pin 3. Therefore, pin 2 (Ec+) is the

Figure 5. Simplified Internal Circuit Diagram

4. For more details about the internal workings of the 2181 Series of VCAs, see An Improved Monolithic Voltage-Controlled
mplifier, by Gary K. Hebert (Chief Technology Officer, for THAT Corporation), presented at the 99th convention of the

udio Engineering Society, New York, Preprint number 4055

THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA

Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com

Copyright © 2008, THAT Corporation

positive control port, while pin 3 (Ec-) is the