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參數(shù)資料
| 型號(hào)： | THAT2150A |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | IC Voltage-Controlled Amplifiers |
| 中文描述： | IC電壓控制的放大器 |
| 文件頁(yè)數(shù)： | 4/10頁(yè) |
| 文件大?。?/td> | 144K |
| 代理商： | THAT2150A |
T heory of Operation
The THAT 2150 Series VCAs are designed for high
performance in audio-frequency applications requiring
exponential gain control, low distortion, wide dynamic
range and low dc bias modulation. These parts control
gain by converting an input current signal to a bipolar
logged voltage, adding a dc control voltage, and re-con-
verting the summed voltage back to a current through
a bipolar antilog circuit.
Figure 6 presents a considerably simplified internal
circuit diagram of the IC. The ac input signal current
flows in pin 1, the input pin. The internal op amp
works to maintain pin 1 at a virtual ground potential
by driving the emitters of Q1 and (through the
Voltage
Bias Generator
) Q3. For positive input currents
(I
in
de-
fined as flowing into pin 1), the op amp drives the emit-
ter of Q1 negative, turning off its collector current,
while simultaneously driving the emitter of Q3 nega-
tive, turning it on. The input signal current, therefore,
is forced to flow through Q3 and D3.
Logging & Antilogging
Because the voltage across a base-emitter junction
is logarithmic with collector current, the voltage from
the base of Q3 to the cathode of D3 is proportional to
the log of the positive input current. The voltage at the
cathodes of D3 and D4 is therefore proportional to the
log of the positive input currents plus the voltage at
pin 3, the negative control port. Mathematically,
V
3
=
E
C
2
V
T
ln
I
C
3
I
S
,
where
V
3
is the voltage at the junction of D3 and D4;
V
T
is the thermal voltage, kT
q;
I
C3
is the collector cur-
rent of Q3; and I
S
is the reverse-saturation current of
Q3. It is assumed that D3 matches Q3 (and will be as-
sumed that they match Q4 and D4, as well).
In typical applications (see Figure 3, Page 3), pin 4
is connected to a voltage source at ground or nearly
ground potential. Pin 8 is connected to a virtual
ground (usually the inverting input of an op amp with
negative feedback around it). With pin 4 near ground,
and pin 8 at virtual ground, the voltage at the cathodes
of D3 and D4 will cause an exponentially-related cur-
rent to flow in D4 and Q4, and out via pin 8. A similar
equation governs this behavior:
V
3
=
E
C
+
2
V
T
ln
I
C
4
I
S
.
Exponential Gain Control
The similarity between the two preceeding equations
begs further exploration. Accordingly:
V
3
=
E
C
+
2
V
T
ln
I
C
4
I
S
=
E
C
2
V
T
ln
I
C
3
I
S
E
C
+
E
C
=
2
V
T
ln
I
C
4
I
S
2
V
T
ln
I
C
3
I
S
=
2
V
T
ln
I
C
4
I
C
3
.
Rearranging terms,
I
C
4
=
I
C
3
e
E
C
+
E
C
2
V
T
.
If pin 3 and pin 4 are at ground potential, the cur-
rent in Q4/ D4 will precisely mirror that in Q3/ D3.
When pin 3 is positive with respect to pin 4, the voltage
across the base-emitter junction of Q3 is higher than
that across the base-emitter junction of Q4, so the
Q4/ D4 current remains proportional to, but less than,
the current in Q3/ D3. In the same manner, a negative
voltage at pin 3 with respect to pin 4 causes the
Q4/ D4 current to be proportional to, but greater than
that in Q3/ D3.
The ratio of currents is exponential with the differ-
ence in the voltages E
C+
and E
C–
, providing convenient
“deci-linear” control. Mathematically, this is:
A
V
=
I
C
4
I
C
3
=
e
E
C
+
E
C
2
V
T
, where A
V
is the current gain.
For pin 4 at or very near ground, at room tempera-
ture (25C), allowing for a 10C internal temperature
rise, and converting to a base of 10 for the exponential,
this reduces to:
-
+
Q1
Q4
Q3
Q2
D3
D1
5
4
8
3
1
2
(SYM)
V-
IN
Ec+
Ec+
OUT
Ec-
Generator
Bias
Voltage
D2
D4
V3
Iin
Figure 6. Simplified Internal Circuit Diagram
THAT Corporation; 734 Forest Street; Marlborough, Massachusetts 01752; USA
Tel: (508) 229-2500; Fax: (508) 229-2590; Web: http:/ / www.thatcorp.com
Page 4
2150 Series IC VCAs
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PDF描述 |
|---|---|
| THAT2151 | IC Voltage-Controlled Amplifiers |
| THAT2155 | IC Voltage-Controlled Amplifiers |
| THAT2181 | Trimmable IC Voltage Controlled Amplifiers |
| THAT2181A | Trimmable IC Voltage Controlled Amplifiers |
| THAT2181B | Trimmable IC Voltage Controlled Amplifiers |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| THAT2151 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:IC Voltage-Controlled Amplifiers |
| THAT2155 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:IC Voltage-Controlled Amplifiers |
| THAT2180A | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Pre-Trimmed IC Voltage Controlled Amplifiers |
| THAT2180AL08-U | 制造商:THAT CORPORATION 功能描述:AMP VOLT CONTROLLED PRETRIM 2180 制造商:THAT CORPORATION 功能描述:AMP, VOLT CONTROLLED, PRETRIM, 2180 制造商:THAT CORPORATION 功能描述:AMP, VOLT CONTROLLED, PRETRIM, 2180; IC Function:Voltage Controlled Amplifier; Brief Features:Exponential Gain Control, Wide Gain Range; Supply Voltage Min:-18V; Supply Voltage Max:18V; Operating Temperature Min:0C; Operating ;RoHS Compliant: Yes |
| THAT2180B | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Pre-Trimmed IC Voltage Controlled Amplifiers |
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