that4320 THAT Corporation, that4320 Datasheet - Page 13

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

Document 600045 Rev 04
encoder. This is where the input to the RMS detector is
derived. The input circuit for the RMS detector in-
cludes another pre-emphasis network which provides a
maximum of 10 dB of pre-emphasis (R
approximately 2.9 kHz (f
6.5 kHz (f
the RMS and VCA pre-emphasis curves. This net-
work feeds the input of the RMS detector, which is a
virtual ground referenced to V
“The RMS Detector - In Brief ” (on page 9), the RMS
detector is capable of driving large spikes of current
into the averaging capacitor C
currents from upsetting circuit grounds, it is neces-
sary to bypass V
end of the C
equal to or greater than the value of C
grounded ends of these two capacitors should be
connected together before being tied to the rest of
This effectively centers the rising sections of both
As described in the Theory of Operation section
f
1
f
V
2
4
Un-used and available
for low noise pre-amp
or other circuits
REF
). These frequencies were chosen such that
20 dB / ~100 s pre-emphasis
V
=
In
CC
TIME
= +5 V
f
27
26
3
CC
10u
C3
+
-
with a capacitor (C
OA1
f
U1B
4320
4
to a point very near the grounded
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
28
μ
25
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
10n
C9
3
), and stopping at around
10k0
R1
REF
TIME
1k10
100n
R3
C12
.
. To prevent these
6dB Static Gain
4
10
23
/C
in Figure 12)
Figure 12. THAT4320 2:1 Encoder Circuit
Copyright © 2007, THAT Corporation
100n
4320
C11
Optional Clipper/Overload Protection
In
U1A
Ec+
14
4k99
R9
4
VCA
), rising at
TIME
OA2
+
-
10k0
R7
. The
2
3
V
21
V
REF
PTAT
6dB Static Gain
22p NPO
2k49
OA3
R13
20k0
4k99
D1
D2
C5
R4
R8
20
(C
C10
10u
8
TIME
V
U1C
4320
REF
Out
9k09
the ground system. Doing so will ensure that the
current spikes flow within the local loop consisting
of the two capacitors, and stay out of the ground sys-
tem. This requirement applies to the decoder and
other applications of the THAT4320 as well.
when the RMS input current is equal to the timing
current (internally set to ~7.5 μA). A low-frequency
voltage level of -26 dBu was chosen as the desired
zero dB reference since this, in conjunction with the
applied static gain, makes optimal use of the avail-
able gain in the VCA. Then, the RMS detector’s
low-frequency input resistance can be calculated as:
for R
calculated based on the desired pre-emphasis start-
ing frequency.
A Signal Limiter for Power Amplifiers, the compres-
RMS
)
R5
7
CT
The output of the RMS detector is zero volts
R
From the desired 10 dB pre-emphasis, the value
In THAT Corporation’s application note AN103,
10 dB /
In
2
10
6
=
NPO 2.5%
can then be calculated to be 2.26 kΩ. C
V
2k05
0 775 10
CC
R6
4k99
.
2k26
R10
3n3
~
R2
C8
20 kHz Butterworth LPF
C4
22u
50 s pre-emphasis
7 5
.
×
μ
60 Hz HPF
μ
100n
C13
A
C7
470n
22u
C1
1n
NPO
2.5%
C14
10n
C2
−
20
26
FILT
18
≅
17
4 99
U1D
OA4
4320
+
-
.
15
13
14
U1E
4320
V
Filt
Gnd
k
16
CC
Ω
Decoder Out
V
V
Gnd
PTAT
REF
9
11
1
100n
V
C6
V
PTAT
REF
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