THAT4311 ETC, THAT4311 Datasheet - Page 8

• Manufacturer Part Number: THAT4311
• Description: Low-voltage/ Low-power Analog Engine Dynamics Processor
• Manufacturer: ETC

Page 8
placed well below the frequency range of interest.
For an audio-band detector, a typical value would be
5Hz, or a 32ms time constant (t). The filter’s time
constant is determined by an external capacitor at-
tached to the CT pin, and an internal current source
(I
grammed via the IT pin: current in IT is mirrored to
I
time
(0.026 ´ CT) / I
matics of rms detection, the attack and release time
constants are fixed in their relationship to each other.
same constant of proportionality as the VCA gain
control: 6.1mV/dB. The detector’s zero dB reference
(Iin0, the input current which causes zero volts out-
put), is determined by IT as follows: Iin0=IT. The
detector output stage is capable of sinking or sour-
cing l00mA.
tor circuitry and that of the THAT 2252 RMS Detec-
tor are as follows:
nally balanced by design, and cannot be balanced via
an external control. The 4311 will typically balance
positive and negative halves of the input signal within
TIME
TIME
The log-domain filter cutoff frequency is usually
The DC output of the detector is scaled with the
Differences between the 4311’s RMS-Level Detec-
1. The rectifier in the 4311 RMS Detector is inter-
) connected to CT. The current source is pro-
with a gain of approximately one. The resulting
constant
Signal In
N/C
N/C
100n
C7
1
2
T
. Note that, as a result of the mathe-
THAT 4311
Control Port Drive
IN
Iset
+5
t
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
10
11
U1B
RMS
is
THAT 4311
Vcc
Vee
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
OUT
+
TC
47u
approximately
U1E
C1
Vref
4
5
Vref 9
Cap
N/C
N/C
20k
R1
8
+
Fig 18. Circuit showing gain control at E
17
10u
C5
IN
equal
EC+
51R
R3
15
VCA
Vref
51k
EC-
R4
16
+
14
SYM
to
50k
22u
R5
C8
OUT
13
N/C
Vref
+5
OA3
47p
Vref
C2
±1.5%, but in extreme cases the mismatch may
reach +20%. However, a 20% mismatch will not sig-
nificantly increase ripple-induced distortion in dy-
namics processors over that caused by signal ripple
alone.
is determined by the combination of an external ca-
pacitor (connected to the CT pin) and an internal,
programmable current source. The current source is
equal to IT. Normally, a resistor is not connected di-
rectly to the CT pin on the 4311.
not adjustable via an external current source. How-
ever, as in the 2252, the level match is affected by the
timing current, which, in this case, is drawn from the
IT pin and mirrored internally to CT.
integrated P-channel FETs rather than a bias-current
corrected bipolar differential amplifier.
currents are therefore negligible, improving perfor-
mance at low signal levels.
The Opamps - in Brief
general purpose applications. All are 5MHz opamps
with slew rates of approximately 2V/ms. All use bipo-
lar PNP input stages. However, the design of each is
optimized for its expected use. Therefore, to get the
U1A
THAT 4311
U1C
3
20k
R2
2. The time constant of the 4311’s RMS detector
3. The zero dB reference point, or level match, is
4. The input stage of the 4311 RMS detector uses
The three opamps in the 4311 are intended for
OA2
12
THAT 4311
Low-voltage, Analog Engine
7
6
C+
Signal Out
N/C
N/C
N/C
19
20
U1D
OA1
Preliminary Information
THAT 4311
®
Dynamics Processor
18
N/C
Input bias