Wide Dynamic Range: >120 Wide Gain Range: >130 Exponential (dB) Gain C
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Blackmer® Trimmable Voltage Controlled Amplifiers THAT 2181A, 2181B, 2181C FEATURES
Wide Dynamic Range: >120 Wide Gain Range: >130 Exponential (dB) Gain Control Distortion: 0.0025 (typical 2181A) 0.005 (typical 2181C) Wide Gain-Bandwidth: Dual Gain-Control Ports (pos/neg) Pin-Compatible with 2150-Series
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Description
THAT 2181 Series integrated-circuit voltage controlled amplifiers (VCAs) very highperformance current-in/current-out devices with opposing-polarity, voltage-sensitive control ports. They offer wide-range exponential control gain attenuation with signal distortion. parts selected after packaging based primarily after-trim control-voltage feedthrough performance. design takes advantage fully complementary dielectric isolation process which offers closely matched NPN/PNP pairs. This delivers performance unobtainable through conventional process, integrated discrete. parts available three grades, allowing user optimize cost performance. Both 8-pin single-in-line (SIP) surface mount (SO) packages available.
Name Input
BIAS CURRENT COMPENSATION
VGnd Output
MULTIPLIER
Input
Output
Iadj
Table Assignments Trimmed @1V,1kHz,0dB Plastic Plastic
Iset
0.01% 0.02% 0.05%
2181AL08-U 2181AS08-U 2181BL08-U 2181BS08-U 2181CL08-U 2181CS08-U
Figure 2181 Series Equivalent Circuit Diagram
Table Ordering information
THAT Corporation; Sumner Street; Milford, Massachusetts 01757-1656; Tel: 9200; Fax: 0990; Web: www.thatcorp.com Copyright 2008, THAT Corporation Document 600030
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THAT 2181 Series Blackmer® Trimmable VCAs
SPECIFICATIONS Absolute Maximum Ratings
Positive Supply Voltage (VCC) Negative Supply Voltage (VEE) Supply Current (ICC) Maximum (EC-) Power Dissipation (PD) Operating Temperature Range (TOP) Storage Temperature Range (TST) +125
Recommended Operating Conditions
Parameter Positive Supply Voltage Symbol Conditions ISET 2181A 0.35 2181B 0.35 2181C 0.35 Units
Negative Supply Voltage Bias Current Signal Current ISET IOUT
Electrical Characteristics
2181A Parameter Supply Current Equiv. Input Bias Current Input Offset Voltage Output Offset Voltage Symbol VOFF(IN) VOFF(OUT) Conditions signal Signal Signal Rout gain gain gain 2181B 2181C Units
Gain Cell Idling Current Gain-Control Constant
IIDLE
=25°C (TCHIP35°C) gain (Fig. /Gain (dB) /Gain (dB) /TCHIP TCHIP 27°C gain
-6.2 -6.1
-6.0
-6.2 -6.1
-6.0
-6.2 -6.1
mV/dB -6.0 mV/dB %/°C
Gain-Control TempCo Gain-Control Linearity Isolation Output Noise
+0.33
+0.33
+0.33
EC+= -360mV,EC-=+360mV en(OUT) Rout gain gain Signal
-2.6
-2.6
-2.6
Voltage
-3.1 -2.85
-3.1 -2.85
-3.2 -2.85
specifications subject change without notice. Unless otherwise noted, VCC=+15V, VEE= -15V. Test circuit shown Figure adjusted minimum kHz, -Ec+ Stresses above those listed under "Absolute Maximum Ratings" cause permanent damage device. These stress ratings only; functional operation device these other conditions above those indicated operational sections this specification impli Exposure absolute maximum rating conditions extended periods affect device reliability.
THAT Corporation; Sumner Street; Milford, Massachusetts 01757-1656; Tel: 9200; Fax: 0990; Web: www.thatcorp.com Copyright 2008, THAT Corporation
THAT 2181 Series Blackmer® Trimmable VCAs
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Electrical Characteristics (con't)
Parameter Symbol Conditions dBV, gain dBV, gain dBV, gain dBV, gain ROUT 2181A 2181B 2181C Units
Total Harmonic Distortion
0.0025 0.018 0.018 0.004
0.005 0.025 0.025 0.008 +0.5 +0.1
-1.5
0.004 0.025 0.025 0.006
0.008 0.035 0.035 0.010 +1.5 +0.15
-2.5 -0.2
0.005 0.02 0.035 0.07 0.035 0.07 0.015 +2.5 +0.2
V/µs
Slew Rate
Symmetry Control Voltage VSYM 0dB, Minimum -0.5 Gain Control Voltage -0.1
-0.15
2181 Series
EcSYM
OP275
Power Supplies
5.1k
Rsym 680k (2181A) 220k (2181B) 130k (2181C)
Figure Typical Application Circuit
Figure 2181 Series Frequency Response Gain
Figure 2181 Series Noise (20kHz NBW) Gain
THAT Corporation; Sumner Street; Milford, Massachusetts 01757-1656; Tel: 9200; Fax: 0990; Web: www.thatcorp.com Copyright 2008, THAT Corporation
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THAT 2181 Series Blackmer® Trimmable VCAs
Theory Operation
THAT 2181 Series VCAs designed high performance audio-frequency applications requiring exponential gain control, distortion, wide dynamic range control-voltage feedthrough. These parts control gain converting input current signal bipolar logged voltage, adding control voltage, re-converting summed voltage back current through bipolar antilog circuit. Figure presents considerably simplified internal circuit diagram input signal current flows input pin. internal operational transconductance amplifier (OTA) works maintain virtual ground potential driving emitters (through Voltage Bias Generator) Q3/D3 Q1/D1 input current, producing voltage, which represents bipolar logarithm input current. (The voltage junction same shifted four forward drops.)
Figure Gain Control Voltage (EC+, 25°C
Gain Control
Since output, usually connected virtual ground, Q2/D2 Q4/D4 take bipolar antilog creating output current which precise replica input current. (EC+) (EC-) held ground (with connected high impedance current source), output current will equal input current. positive negative, output current will scaled larger than input current. negative positive, output current scaled smaller than input.
Figure Gain Control Voltage (EC-, 25°C
Figure Gain Control Voltage (EC-) with Temp (°C)
normal operation, output current converted voltage opamp-based converter, shown Figure where conversion ratio determined feedback resistor connected between output inverting input. signal path through output opamp non-inverting. scale factor between output input currents gain VCA. Either (Ec+) (Ec-), both, used control gain. Gain exponentially proportional voltage exponentially proportional negative voltage Therefore, (Ec+) positive control port, while (Ec-)
Figure Simplified Internal Circuit Diagram
more details about internal workings 2181 Series VCAs, Improved Monolithic Voltage-Controlled Amplifier, Gary Hebert (Chief Technology Officer, THAT Corporation), presented 99th convention Audio Engineering Society, York, Preprint number 4055. THAT Corporation; Sumner Street; Milford, Massachusetts 01757-1656; Tel: 9200; Fax: 0990; Web: www.thatcorp.com Copyright 2008, THAT Corporation
THAT 2181 Series Blackmer® Trimmable VCAs
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negative control port. Because exponential characteristic, control voltage sets gain linearly decibels. Figure shows decibel current gain 2181 versus voltage Ec+, while Figure shows gain versus Ec-.
Trimming
2181-Series VCAs intended adjusted minimum distortion applying small variable offset voltage pin. Note that there resistor internal 2181 between shown Figure Page usual method applying this offset internal resistor along with larger value resistor form voltage divider connected wiper trim across supply rails. This trim should adjusted minimum harmonic distortion. This usually done applying middle-level, middle-frequency signal (e.g. audio input, setting gain, adjusting trim while observing output. 2181, this adjustment coincides closely with setting which produces minimum control-voltage feedthrough, though settings always identical.
Temperature Effects
logging antilogging depends logarithmic relationship between voltage current semiconductor junction particular, between transistor's IC). well known, this relationship temperature dependent. Therefore, gain log-antilog depends temperature. Figure shows effect temperature negative control port. (The positive control port behaves same manner.) Note that gain regardless temperature. Changing temperature changes scale factor gain 0.33%/°C, which pivots curve about point. Mathematically, 2181's gain characteristic
Feedthrough
Normally, small error term flows (the output). When gain changed, term changes. This control-voltage feedthrough more pronounced with gain; version part produces least feedthrough, version most. Figure typical curves offset gain
Gain
(0.0061)(1+0.0033
where difference between room temperature (25°C) actual temperature, Gain gain decibels. room temperature, this reduces
Gain
0.0061
only positive control port used, this becomes
Gain
0.0061
only negative control port used, this becomes
Figure Representative Offset Gain
Gain
0.0061
Audio Performance
2181-Series design, fabrication testing ensure extremely good audio performance when used recommended. 2181 maintains distortion over wide range gain, signal levels. Figures through show typical distortion performance representative samples each grade part. near unity gain, 2181 behaves much like good opamp, with distortion over entire audio band. Figure shows typical 2181A over frequency gain, with input signal, while Figure details harmonic content distortion typical A-grade part.
Bias Currents
2181 current consumption determined resistor between (V-) negative supply voltage (VEE). Typically, with supplies, resistor which provides approximately This current split into paths: used biasing remainder becomes ICELL shown Figure ICELL furth split parts: about biases core transistors through Q4), rest available input output signal current.
THAT Corporation; Sumner Street; Milford, Massachusetts 01757-1656; Tel: 9200; Fax: 0990; Web: www.thatcorp.com Copyright 2008, THAT Corporation
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THAT 2181 Series Blackmer® Trimmable VCAs
Figure THD+Noise Input Level, Gain
Figure 2181A THD+N Frequency, gain 1kHz
Figure THD+Noise Input Level, +15dB Gain
Figure THD, Typical 2181A, Gain, 1kHz
Figure THD+Noise Input Level, -15dB Gain
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Applications
Input
mentioned above, input output signals currents, voltages. While this often causes some conceptual difficulty designers first exposed this convention, current input/output mode provides great flexibility application. Input (pin virtual ground with negative feedback provided internally (see Figure Page input resistor (shown Figure Page should scaled convert available input voltage current within linear range device. Generally, peak input currents should kept under best distortion performance. Refer Figures through distortion varies with signal level three parts 2181 Series gain. circuit Figure Page used generate these curves. specific application, acceptable distortion will usually determine maximum signal current level which used. Note that, with current-to-voltage converting resistors, distortion remains even input gain, input gain (~10 output). This especially true grades part.
High-Frequency Distortion
choice input resistor additional, subtle effect distortion. Since feedback impedances around internal opamp (essentially Q1/D1 Q3/D3) fixed, values input resistor will require more closed-loop gain from opamp. Since open-loop gain naturally falls high frequencies, asking much gain will lead increased high-frequency distortion. best results, this resistor should kept above.
Stability
additional consideration stability: internal intended operation with source impedances less than high frequencies. most audio applications, this will present problem.
Coupling
quiescent voltage level input (the input offset voltage) approximately but, many general-purpose opamps, this well controlled. input currents will cause output which will modulated gain; this cause audible thumps. input coupled, input currents generated input offset voltage 2181 itself, offsets stages preceeding 2181. Therefore, capacitive coupling almost mandatory quality audio applications. Choose capacitor which will give acceptable frequency performance application.
Distortion Noise
designer trade noise distortion decreasing current-to-voltage converting resistors used input output Figure Page every these resistor values decreased, voltage noise output OP275 reduced example, with resistors, output noise floor drops -104 (typical) gain reduction noise because lower than) Conversely, more important than noise performance, increasing these resistors will increase noise level while reducing distortion maximum voltage levels. Furthermore, maximum signal levels higher lower) than traditional rms, these resistors should scaled accommodate actual voltages prevalent circuit. Since 2181 handles signals currents, these even operate with signal levels exceeding 2181's supply rails, provided appropriately large resistors used.
Summing Multiple Input Signals
Multiple signals summed multiple resistors, just with inverting opamp configuration. such case, single coupling capacitor located next rather than multiple capacitors driven ends summing resistors. However, take care that capacitor does pick stray signals.
Output
Output (pin intended connected virtual ground node, that current flowing converted voltage (see Figures 15). Choose external opamp good audio performance. feedback resistor should chosen based desired current-to-voltage conversion constant. Since input resistor determines voltage-to-current conversion input,
THAT Corporation; Sumner Street; Milford, Massachusetts 01757-1656; Tel: 9200; Fax: 0990; Web: www.thatcorp.com Copyright 2008, THAT Corporation
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familiar ratio inverting opamp will determine overall voltage gain when 2181 current gain. Since performs best settings near unity gain, input feedback resistors provide design-center gain loss, necessary. small feedback capacitor around output opamp needed cancel output capacitance VCA. Without this capacitance will destabilize most opamps. capacitance typically
Mathematically, this expressed ICELL Peak (IIN) Peak (IOUT) ICELL ISET Therefore, ISET Peak (IIN) Peak (IOUT) voltage (pin four diode drops below ground, which, 2181, approximately -2.85 Since this connects (high impedance) current supply, voltage supply, bypassing normally necessary.
Power Supplies
Positive
positive supply connected directly (pin special bypassing necessary, good practice include small electrolytic (~0.1 ceramic capacitor close PCB. Performance particularly dependent supply voltage. lowest permissible supply voltage determined input output currents plus ISET which must supplied through output internal transconductance amplifier down through core voltage bias generator. Reducing signal currents help accommodate supply voltages. THAT Corporation intends publish application note covering operation supply voltages. Please inquire availability. highest permissible supply voltage fixed process characteristics internal power consumption. nominal limit.
Ground
(pin used ground reference VCA. non-inverting input internal opamp connected here, various portions internal bias network. used additional input pin.
Voltage Control
Negative Sense
(pin negative voltage control port. This point controls gain inversely with applied voltage: positive voltage causes loss, negative voltage causes gain. described Page current gain unity when with respect varies with voltage approximately -6.1 mV/dB, room temperature.
Positive Sense
mentioned earlier, (pin positivesense voltage control port. typical circuit using this approach shown Figure (Pin should grounded, (pin driven from low-impedance voltage source. Using opposite sense control sometimes save inverter control path.
Negative
negative supply terminal (pin Unlike normal negative supply pins, this point intended connected current source ISET (usually simply resistor VEE), which determines current available device. mentioned before, this source must supply input output signal currents, plus bias rest) minimum value this current over required signal currents. Usually, ISET should equal most audio applications with supplies. Higher bias levels limited value, largely because core transistors become ineffective logging antilogging currents over
Positive Negative
also possible (and sometimes advantageous) drive both control ports, either with differential drive which case, control sensitivities each port summed), through different control signals. There reason both control ports cannot used simultaneously.
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Symmetry
(pin actually sort additional positive-sense control port. provided allow mismatches core transistors adjusted after packaging installation circuit board. should only used this purpose. Connect only high-impedance source shown Figures
output impedance opamp typically rises high frequencies because open loop gain falls frequency increases. typical opamp's output impedance therefore inductive high frequencies. Excessive inductance control port source impedance cause oscillate internally. such cases, resistor series with capacitor from control port ground will usually suffice prevent instability.
Control Port Drive Impedance
control ports (pins through connected directly bases logging and/or antilogging transistors. accuracy logging antilogging dependent ECvoltages being exactly desired control gain. base current core transistors will follow collector currents, course. Since collector currents signal-related, base currents therefore also signal-related. Should source impedance control voltage(s) large, signal-related base currents will cause signal-related voltages appear control ports, which will interfere with precise logging antilogging, turn causing distortion. 2181 Series VCAs designed operated with zero source impedance pins high source impedance realize performance designed into 2181, keep source impedance control voltage driver well under This often suggests driving control port directly with opamp. However, closed-loop
Noise Considerations
second nature among good audio designers consider effects noisy devices signal path. well known, this includes only active devices such opamps transistors, extends choice impedance levels well. High value resistors have higher inherent thermal noise, noise performance otherwise quiet circuit easily spoiled wrong choice impedance levels. Less well known, however, effect noisy circuitry high impedance levels control path voltage-control circuitry. 2181 Series VCAs like multipliers: when signal present signal input, noise control input rejected. when measuring noise absence signal most everyone does), even very noisy control circuitry often goes unnoticed. However, noise control port these parts will cause noise modulation signal. This become significant care taken drive control ports with quiet signals.
2181 Series
EcSYM
OP275
Power Supplies
5.1k
Rsym 680k (2181A) 220k (2181B) 130k (2181C)
Figure Positive Control Port using THAT Corporation; Sumner Street; Milford, Massachusetts 01757-1656; Tel: 9200; Fax: 0990; Web: www.thatcorp.com Copyright 2008, THAT Corporation
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THAT 2181 Series Blackmer® Trimmable VCAs
2181 Series VCAs have small amount inherent noise modulation because class biasing scheme, where shot noise core transistors reaches minimum with signal, increases with square root instantaneous signal current. However, optimum circuit, noise floor rises only with signal unity gain noise modulation. contrast, unity-gain connected, non-inverting 5534 opamp used directly drive control port, noise floor will rise noise modulation. avoid excessive noise, must take care quiet electronics throughout control-voltage circuitry. useful technique process control voltages multiple eventual control constant (e.g., mV/dB times higher than requires), then attenuate control signal just before final drive amplifier. With careful attention impedance levels, relatively noisy opamps used final stage.
null minimum varies with frequency. often possible counteract small amount pure fundamental picked control path "misadjusting" symmetry setting. Since amount pickup usually varies with frequency, optimum trim setting will vary with frequency level. useful technique confirm this problem temporarily bypass control port ground modest-sized capacitor (e.g., distortion diminishes, signal pickup control path likely cause.
Temperature Sensitivity
shown Equation (Page gain 2181 sensitive temperature proportion amount gain loss commanded. constant proportionality 0.33% decibel gain commanded, degree Celsius, referenced 27°>C (300°K). This means that gain, there change gain with temperature. However, -122 gain will room temperature, will 20.66 temperature 10°C lower. most audio applications, this change with temperature little consequence. However, necessary, compensated resistor embedded control voltage path whose value varies with temperature same rate 0.33%/°C. Such parts available from Components, Inc, www.rcd-comp.com, KOA/Speer Electronics, www.koaspeer.com.
Stray Signal Pickup
also common practice among audio designers design circuit boards minimize pickup stray signals within signal path. with noise control path, signal pickup control path adversely effect performance otherwise good VCA. Because multiplier, 2181 produces second harmonic distortion audio signal itself present control port. Only small voltage control port required: little signal increase distortion over 0.01%. This frequently seen high frequencies, where capacitive coupling between signal control paths cause stray signal pickup. Because signal levels involved very small, this problem difficult diagnose. clue presence this problem that symmetry
Closing Thoughts
THAT Corporation welcomes comments, questions suggestions regarding these devices, their design application. engineering staff includes designers have decades experience applying parts. Please feel free contact discuss your applications detail.
THAT Corporation; Sumner Street; Milford, Massachusetts 01757-1656; Tel: 9200; Fax: 0990; Web: www.thatcorp.com Copyright 2008, THAT Corporation
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Package Information
THAT 2181-series available 8-pin 8-pin packages. Package dimensions shown Figure below; Pinouts given Table page Ordering information provided Table also page 2181-series packages entirely lead-free. lead-frames copper, plated with successive layers nickel, palladium, gold. This approach makes possible solder these devices using leadfree lead-bearing solders. Neither lead-frame plastic mold compound used 2181-series contains hazardous substances specified European Union's Directive Restriction Certain Hazardous Substances Electrical Electronic Equipment 2002/95/EG January 2003
Package Characteristics
Parameter Through-hole package Thermal Resistance Symbol Conditions Figure dimensions package soldered board Units
Environmental Regulation Compliance Surface-mount package Thermal Resistance Soldering Reflow Profile Moisture Sensitivity Level
Complies with January 2003 RoHS requirements Figure dimensions package soldered board
JEDEC JESD22-A113-D Above-referenced JEDEC soldering profile
Environmental Regulation Compliance
Complies with January 2003 RoHS requirements
ITEM MILLIMETERS 19.5 +0.2/-0 1.25 0.65 0.85 2.54 ±0.2 +0.2/-0 +0.1/-0 10.5 ±0.5 ±0.5 17.78 ±0.3 INCHES 0.77 +0.008/-0 0.049 0.026 0.033 0.100 ±0.008 0.04 0.05 0.23 +0.008/-0 0.11 +0.004/-0 0.413 ±0.02 0.05 0.012 0.14 ±0.02 0.700 ±0.012 TYP.
Figure (SIP) Version Package Outline Drawing
Figure (SO) Version Package Outline Drawing
THAT Corporation; Sumner Street; Milford, Massachusetts 01757-1656; Tel: 9200; Fax: 0990; Web: www.thatcorp.com Copyright 2008, THAT Corporation
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THAT 2181 Series Blackmer® Trimmable VCAs
Notes
THAT Corporation; Sumner Street; Milford, Massachusetts 01757-1656; Tel: 9200; Fax: 0990; Web: www.thatcorp.com Copyright 2008, THAT Corporation
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