that4320 THAT Corporation, that4320 Datasheet - Page 14

• Manufacturer Part Number: that4320
• Description: Pre-trimmed Low-voltage Low-power Analog Engine Dynamics Processor Ic
• Manufacturer: THAT Corporation

Page 14
sion ratio for a feedback compressor was derived
using the analytical technique described in AN101A,
The Mathematics of Log Based Dynamics Proces-
sors. This technique is referred to as ‘working in the
log domain’. Using these methods, it can be shown
that the compression ratio (C.R.) of a feedback com-
pressor is
side chain.
VCA gain control port (E
ured for an inverting gain of one. This fixes the com-
pression ratio at 2:1. Note that the negative sign in
the side chain gain makes this circuit a compressor.
C.R. = 1 + A,
where A is the absolute value of the gain of the
The RMS detector’s output is connected to the
Encoder Out
C12
22u
V
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
C6
1u
REF
V
CC
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
100n
C13
100k
R3
C+
9k09
) through OA2, config-
R1
C4
22u
C1
3n3 NPO
2k05
15
13
14
R6
20 kHz Butterworth LPF
Figure 13. THAT4320 2:1 Decoder Circuit
Copyright © 2007, THAT Corporation
U1E
4320
V
Filt
Gnd
CC
C8
1n
V
V
Gnd
PTAT
REF
27
26
9
11
1
+
-
OA1
V
U1B
4320
PTAT
-12dB Static Gain
28
25
2u2
C3
C7
100n
47p
C9
The decoder
2:1 expander, an arrangement intended to comple-
ment the encoder in Figure 12. This circuit is opti-
mized for low-voltage operation, as might be the
case for a decoder in an in-ear monitoring system
which will run from battery power.
in Figure 12 is now in the feedback loop of OA
This provides de-emphasis. The VCA is set up with
-12dB of static gain to keep output signal levels low
for battery operation. Because the VCA is not stable
unless it sees a high frequency source impedance of
5 kΩ or less, R
pensation to maintain stability.
Butterworth low-pass filter. This ensures that noise
470n
C14
10n
C2
V
4k99
40k2
REF
Figure 13 shows the THAT4320 configured as a
The pre-emphasis network from the VCA input
OA
R5
R7
100n
C14
1
2k26
4k99
R8
R2
THAT4320 Pre-trimmed Low-voltage Low-power
U1A
4320
is used to implement another 20 kHz
60 Hz HPF
23
6
4
In
Ec+
U1C
4320
In
5
VCA
Analog Engine® Dynamics Processor IC
RMS
7
and C
OA2
CT
20 dB / ~ 100 s de-emphasis
+
Out
-
C10
10u
2
3
21
V
8
REF
9
provide the necessary com-
OA3
+
C11
10n
-
22p NPO
C5
10k0
μ
R8
20
1k10
R4
17
18
Un-used
V
-
OA4
+
U1D
4320
REF
Out
16
3
;