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參數(shù)資料
| 型號： | THAT4311 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Low-voltage, Low-power Analog Engine?? Dynamics Processor |
| 中文描述： | 低電壓，低功耗模擬引擎？？動態(tài)處理器 |
| 文件頁數(shù)： | 7/12頁 |
| 文件大?。?/td> | 230K |
| 代理商： | THAT4311 |
As mentioned, for proper operation, the same
voltage must be applied to EC+ and SYM, except for
a small (±2.5 mV) DC bias applied
between
these
pins.
This bias voltage adjusts for internal mis-
matches in the VCA gain cell which would otherwise
cause small differences between the gain of positive
and negative half-cycles of the signal. The voltage is
usually applied via an external trim potentiometer
(R7 in Fig 2), which is adjusted for minimum signal
distortion at unity (zero dB) gain.
The VCA may be controlled via EC-, as shown in
Fig 17, or via the combination of EC+ and SYM.
This connection is illustrated in Fig 18.
this latter figure shows only that portion of the cir-
cuitry needed to drive the positive VCA control port;
circuitry associated with OA1, OA2 and the RMS de-
tector has been omitted.
Note that
While the 4311’s VCA circuitry is very similar to
that of the THAT 2180 Series VCAs, there are several
important differences, as follows:
1. Supply current for the VCA is fixed internally.
Approximately 500 A is available for the sum of in-
put and output signal currents.
2. The signal current output of the VCA is inter-
nally connected to the inverting input of an on-chip
opamp.
around this opamp, this node is brought out to a pin.
In order to provide external feedback
3. The input stage of the 4311 VCA uses inte-
grated P-channel FETs rather than a bias-current
corrected bipolar differential amplifier.
currents have therefore been reduced.
Input bias
The RMS Detector - in Brief
The THAT 4311’s detector computes RMS level
by rectifying input current signals, converting the rec-
tified current to a logarithmic voltage, and applying
that voltage to a log-domain filter. The output signal
is a DC voltage proportional to the decibel-level of the
RMS value of the input signal current.
component (at twice the input frequency) remains su-
perimposed on the DC output. The AC signal is at-
tenuated by a log-domain filter, which constitutes a
single-pole roll-off with cutoff determined by an ex-
ternal capacitor and a programmable DC current.
Some AC
As in the VCA, input signals are currents to the
RMS IN pin. This input is a virtual ground biased at
VREF, so a resistor (R11 in Fig 2) is normally used to
convert input voltages to the desired current.
level detector is capable of accurately resolving sig-
The
nals well below 10mV (with a 10k
However, if the detector is to accurately track such
low-level signals, AC coupling is normally required.
input resistor).
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
Rev. 08/30/01
Preliminary Information
Page 7
IN
17
12
OUT
VCA
EC-
EC+
SYM
OA3
THAT 4311
Vref
U1A
Iset
THAT 4311
2
TC
5
IN
1
OUT
4
RMS
U1B
3
7
OA2
Vref
6
U1C
THAT 4311
18
19
20
OA1
U1D
THAT 4311
Cap
8
Vee
THAT 4311
10
Vref9
Vcc
11
Vref
U1E
Vref
Vref
R1
20k
R2
20k
C2
R3
51R
R4
51k
R6
10k
R7
264k
C1
+
47u
47p
C3
+
47u
C4
10u
C5
10u
C8
22u
C7
100n
R5
20k
+5
+5
Signal In
RMS Out
Signal Out
C6
+
10u
Control Port Drive
15
14
13
16
+
+
+
Fig 17. Circuit showing gain control at E
C-
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