THAT4311 ETC, THAT4311 Datasheet - Page 9

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

Rev. 08/30/01
Preliminary Information
most out of the 4311, it is useful to know the major
differences among these opamps.
the VCA. is intended for current-to-voltage conver-
sion.
complements that of the VCA, adding negligible noise
at unity gain. Its output section is capable of driving
1mA into a 2kW load.
its typical input referred noise of 6 5 .
opamp of choice for input stages. Its output section
is nominally capable of driving 3mA into a 5kW load.
though is does have anti-paralleled diodes that can
nally designed for noise reduction systems, hence the
emphasis on those parameters in the specifications.
Its low power consumption, integration, and similar-
ity to the THAT 4301, however, extend its utility to a
variety of other products and applications. The cir-
cuit of Fig 19, shows a typical application for the
THAT 4311. This simple compressor/limiter design
features adjustable hard-knee threshold, compres-
OA3, being internally connected to the output of
OA1 is the quietest opamp of the three, and with
OA2 is best suited for control voltage processing,
As noted previously, the THAT 4311 was origi-
In
Its input noise performance, at 7 5 .
Vin0=-10dBu
+
47u
C3
267k
Threshold
28k7
R6
R7
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
1
2
THAT 4311
U1B
Iset
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
IN
R12
20k
RMS
+5
OUT
TC
4
5
Fig 19. Simple compressor / limiter using the THAT 4311
R11
51k
4k99
+
R8
C4
10u
nV
Application Information
Vref
/
1N4148
10u
C6
3
CR1
+
Hz, is the
nV
OA2
U1C
THAT4311
100n
C7
/
6
7
Hz,
10k
R9
1N4148
CR2
+5
R10
82k
10
11
Vref
THAT 4311
Vcc
Vee
Gain
R13
10k
U1E
1k43
Vref
R14
be used to fashion it into a clipper. (However in most
applications where a clipper is needed, it’s preferable
to place it around OA3). OA2’s input noise is compa-
rable to OA3 and its output drive is comparably to
OA1.
The Reference Voltage - In Brief
detectors require a reference voltage between the pos-
itive and negative power supplies, and to supply this,
the THAT 4311 provides an on-chip, 2V reference
about which the VCA, the RMS detector, and OA2 are
biased. This reference is a buffered band-gap refer-
ence that is amplified to 2V. Pins are provided for fil-
ter capacitors at both the input and the output of the
buffer, which are labeled CAP and VREF respectively.
sion ratio, and static gain. The applications discus-
sion in this data sheet will center on this circuit for
the purpose of illustrating important design issues.
Signal Path
input pin is a virtual ground with negative feedback
provided internally. An input resistor (R1, 20kW) is
required to convert the AC input voltage to a current
R18
50k
Compression
Ratio
Vref
Cap
+5
THAT Corporation’s log/anti-log VCAs and RMS`
As mentioned in the section on theory, the VCA
9
8
+
47u
C1
+
10u
C8
R15
R17
10k
82k
20k
R5
+
Vref
20k
R1
C9
22u
+5
19
20
Vref
OA1
17
U1D
4k99
100n
R16
THAT4311
C5
IN
EC+
51R
33k
R4
R3
18
15 14
VCA
EC-
16
SYM
OUT
Vref
13
OA3
C2
47p
U1A
THAT4311
20k
R2
12
Out
Page 9