that4320 THAT Corporation, that4320 Datasheet - Page 10

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

Page 10
its supply voltage the difference between V
V
nection for this opamp, the design must provide a
negative supply below ground to this pin. By doing,
so, OA
available to the rest of the IC. Because OA
monly used as a pre-amp before a noise reduction
compressor based on the rest of the chip, headroom
is most critical at this point. (The VCA will reduce
the audio signal’s dynamic range to a more manage-
able level for subsequent stages.) The rest of the
chip can run from +5 V and ground to maintain low
power dissipation, while only OA
±5 V supply to gain additional headroom.
is +5 V. If V
swing at OA
OA
instead, V
OA
crease in dynamic range!
OA
the least general purpose of the four opamps. It is
externally compensated, and requires at least 22 nF
at its output to remain stable. This was a deliberate
design choice based on several factors including the
relatively limited bandwidth and voltage swing re-
quired for the VCA control port and the importance
of low noise (and low RF content) at this node. Addi-
tionally, the capacitive high-frequency output imped-
ance guarantees stability in the VCA.
control port signal (consisting primarily of dc with
added low frequency content), OA
dc at the expense of ac performance. This opamp
has limited input compliance (±1 V common mode
range), is relatively slow (120 kHz gain-bandwidth
product with a typical 100 nF capacitive load), has
low open-loop gain (57 dB with the typical 10 kΩ re-
sistive load), and has approximately a 10 Ω output
impedance. These characteristics, while limiting in
an opamp intended for handling audio signals, are
ideal for the control voltage buffer.
compensating the opamp at its output takes advan-
tage of an often-required RF-bypass capacitor to
minimize noise pickup at the sensitive VCA control
port.
OA
currents into voltage signals. It is a unity-gain stable,
7.3 MHz opamp with moderately low input noise of
10.5 nv/ÖHz. This noise floor complements that of
the VCA.
EE
1
1
. Note that this difference must not exceed 16 V.
To gain an advantage from the separate V
To see how this works in practice, suppose V
2
OA
Because it is intended to handle only the VCA
3
OA
‘s output increases to 8.5 V — for a 7.7 dB in-
reaches within ~0.75 V of its supply rails), If,
- Control Voltage Buffer
- VCA Current-to-Voltage Converter
2
3
1
is intended as a control voltage buffer, and is
can gain additional voltage swing over that
is intended to translate the VCA’s output
EE
1
EE
is set to -5 V, the maximum swing at
‘s output is typically 3.5 V (typically,
is set to 0 V (ground), the maximum
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
1
is run from, say, a
2
is optimized for
In particular,
Copyright © 2007, THAT Corporation
1
is com-
CC
EE
con-
and
CC
rectly, OA
output typically swings to within 0.75 V of V
ground, allowing it to support a 1.2 V
from a single +5 V supply (4.75 V
supply). It’s typical slew rate is ~3.2 V/μs, allowing
the part to support maximum level sine waves at up
to 290 kHz on a +5 V supply (75 kHz on a +15 V
supply).
ble of driving up to 150 pF, so it is possible to di-
rectly bypass RF to ground via a small capacitor at
OA
plying at least 1 mA, making it possible to use this
opamp directly as the output stage in lightly loaded
applications. Note, however, that OA
designed to withstand an indefinite short-circuit to a
power supply or ground rail, and a resistor should
be included in series with such outputs to ensure
stability with capacitive loads larger than 150 pF.
OA
age applications. It is a unity-gain stable, 7.3 MHz
opamp with moderately low input noise voltage of
10.5 nv/ÖHz, and moderately low input noise current
of 0.3 pA/ÖHz. Because of it’s lower current noise,
OA
OA
is high.
those of OA
V
a center-tap to provide a synthetic “ground” refer-
ence for its circuitry. The 4320 contains a built-in
resistive divider (at pins 13/14/15), followed by a
buffer, to provide a low-impedance source at approx-
imately half V
sistive divider is brought out to filter the voltage,
thereby minimizing noise in the divider. A large elec-
trolytic capacitor (typically 22 μF or greater) is used
for this purpose.
This is “V
~3 mA at its output. Like OA
capacitance at its output, working against an inter-
nal output impedance of approximately 10 Ω; at
least 22 nF should be used to ensure stability, re-
duce high-frequency output impedance, and attenu-
ate high-frequency noise.
voltage to other sections of circuits beyond the 4320
CC
3
4
1
Like OA
As with the other opamps, OA
4
OA
All other characteristics of OA
For single-supply applications, the 4320 requires
The output of the buffer is available at pin 11.
V
/2 Reference Buffer
‘s output. It’s output section is capable of sup-
in cases where the source impedance feeding it
is a better choice for an audio pre-amp than
REF
- General Purpose OpAmp
4
THAT4320 Pre-trimmed Low-voltage Low-power
is intended for either signal or control volt-
may be used to supply a “ground” reference
3
REF
is optimized for audio performance. It’s
3
1
.
, because it handles audio signals di-
”. The buffer is capable of delivering
CC
Analog Engine® Dynamics Processor IC
. Note that the center tap of the re-
2
, it is compensated by
3
RMS
‘s output is capa-
4
3
‘s output is not
are similar to
RMS
with a +15 V
sine wave
CC
or