that4301 THAT Corporation, that4301 Datasheet - Page 9

• Manufacturer Part Number: that4301
• Description: That Analog Engine Ic Dynamics Processor
• Manufacturer: THAT Corporation

THAT 4301 Analog Engine IC Dynamics Processor
application for THAT 4301. This simple compres-
sor/limiter design features adjustable hard-knee
threshold, compression ratio, and static gain
applications discussion in this data sheet will center
on this circuit for the purpose of illustrating impor-
tant design issues. However, it is posslble to config-
ure many other types of dynamics processors with
THAT 4301. Hopefully, the following discussion will
imply some of these possibilities.
Signal Path
input pin is a virtual ground with negative feedback
provided internally. An input resistor (R
required to convert the ac input voltage to a current
within the linear range of the 4301. (Peak VCA input
currents should be kept under 1 mA for best distor-
tion performance.) The coupling capacitor (C
is
mended to block dc cur-
rent
stages (and from offset
voltage at the input of
the VCA). Any dc current
into the VCA will be
modulated
gain in the VCA, showing
up in the output as
“thumps”. Note that C
in conjunction with R
will set the low fre-
quency limit of the cir-
cuit.
connected to OA
ured as an inverting cur-
rent-to-voltage converter.
OA
nents (R
C
constant
rent-to-voltage
sion. The simplest way
to deal with this is to
recognize that when the
VCA is set for unity
(0 dB) gain, the input to
output voltage gain is
simply R
the case of a single in-
is given in AN100, Basic Compressor Limiter Design. The designs in AN100 are based on THAT Corporation’s
2150-Series VCAs and 2252 RMS Detector, but are readily adaptable to the 4301 with only minor modifications. In
fact, the circuit presented here is functionally identical to the hard-knee circuit published in AN100.
2
, 47 pf) determine the
3
The circuit of Figure 14, Page 9, shows a typical
As mentioned in the section on theory, the VCA
1. More information on this compressor design, along with suggestions for converting it to soft-knee operation,
‘s feedback compo-
The VCA output is
strongly
from
2
2
, 20 kW, and
/R
1
by
, just as in
of
preceding
3
, config-
conver-
varying
recom-
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
cur-
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
1
1
,
,
COMPRESSION
IN
R13
10K
CCW
R12
10K
CW
1
-15
, 20kW) is
+15
CCW
CW
THRESHOLD
1
C7
47uF
C8
Figure 14. Typical Compressor/Limiter Application Circuit
, 47 mf)
C3
1
Applications
. The
1K43
1%
100n
100n
R14
2M00 1%
383K
-15
4k99
R10
47uF
R11
C1
10K0 1%
+15
R8
1%
R6
22uF
1%
C6
verting stage. If, for some reason, more than 0 dB
gain is required when the VCA is set to unity, then
the resistors may be skewed to provide it. Note that
the feedback capacitor (C
The VCA output has approximately 45 pf of capaci-
tance to ground, which must be neutralized via the
47 pf feedback capacitor across R
whereby gain will be proportional to the negative of
the voltage at E
the SYM terminal is returned nearly to ground via a
small resistor (R
50 kW) allows a small voltage to be applied to the
SYM terminal via R
for small mismatches within the VCA gain cell,
thereby reducing even-order distortion products. To
adjust the trim, apply to the input a middle-level,
middle-frequency signal (1 kHz at 1 V is a good
20K0 1%
C9
10K0
VEE
VCC
R1
2M00
R9
+
-
CR1
OA1
R7
1%
The VCA gain is controlled via the E
22p
1%
IN
-15
IT
THAT4301
RMS
10uF
CR2
C4
OUT
CT
C–
. The E
3
IN
, 51 W). The VCA SYM trim (R
EC-
-15
4
(300 kW). This voltage adjusts
R3
VCA
51
GND
VCA SYM
C+
R15
10K0
1%
2
50K
R5
SYM
) is required for stability.
terminal is grounded, and
EC+
OUT
R4
300K
+15
2
.
+
+
-
-
OA3
OA2
C2
C5
20K0
590K
4k99
R17
1%
100N
R2
R16
47pF
1%
1%
C–
terminal,
+15
-15
CCW
CW
OUT
10K
R18
Page 9
GAIN
5
,