4305-DEMO THAT Corporation, 4305-DEMO Datasheet - Page 14

• Manufacturer Part Number: 4305-DEMO
• Description: Audio Modules & Development Tools Low-Cost Dynamics Processor Demo Board
• Manufacturer: THAT Corporation

Specifications of 4305-DEMO

• Description/function: Audio DSPs
• Operating Supply Voltage: 15 V
• Product: Audio Modules
• For Use With/related Products: THAT4305
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Page 14 of 20
reduce the noise gain of U4 at high frequencies,
which slightly reduces the high-frequency noise floor
of the entire circuit. C5 may be omitted for
non-critical applications.
("The RMS Detector - In Brief"), the RMS detector is
capable of driving large spikes of current into the
averaging capacitor C
from upsetting circuit grounds, it is necessary to
bypass V
C
value of C
grounded ends of these two capacitors should be
connected together before being tied to the rest of 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 system.
Companding Systems
The Encoder
simple 2:1 encoder or feedback compressor. The
encoder in a companding system is positioned before
the noisy channel (wireless link, storage system,
TIME
As described in the Theory of Operation section
Figure 17 shows the 4305 configured as a
INPUT
with a capacitor equal to or greater than the
CC
to a point very near the grounded end of
TIME
. This is C13 in Figure 16. The
22u
C1
TIME
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THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
. To prevent these currents
Figure 17. 4305 simple compander circuit - 2:1 encoder (compressor)
20k
R1
220p
C4
5k1
R3
15
U1B
THAT4305
VCA In
EC+
EC-
11
12
VCA Out
5
THAT4305
U1A
RMS Out
10u
C3
etc.). The static gain of this circuit is 1, or zero dB,
and a 5.1 kΩ
capacitor (C4) comprise the compensation network
is required to keep the VCA's input amplifier stable
for all gains.
the VCA's E
Note that the use of the negative-sense control port,
E
detector timing capacitor is set for a release rate of
-125 dB per second by using a value of 10 μF.
timing capacitor (C3) from upsetting circuit grounds
as described in the previous section.
when the RMS input current is equal to the timing
current (internally set to ~7.5 μA). A voltage level of
-28.5 dBV was chosen as the desired zero dB refer-
ence. The RMS detector's input resistance can be
calculated as:
CT
RMS In
13
C-
4
, makes this circuit a compressor.
Since the RMS detector output is tied directly to
C5 serves to keep high currents through the
The output of the RMS detector is zero volts
R
This value also applies to the decoder.
RMS In
22u
C5
2
=
C-
, the compression ratio will be 2:1.
+15V
THAT4305 Pre-trimmed Analog Engine®
10
7.5 A
resistor (R3) along with a 220 pF
−28.5
20
R4
5k1
l 5.1k
20k
22p
R2
C5
U2A
Op-Amp
.
22u
C2
OUTPUT
The RMS