that4315 THAT Corporation, that4315 Datasheet - Page 5

• Manufacturer Part Number: that4315
• Description: Pre-trimmed Low-voltage Low-power Analog Engine
• Manufacturer: THAT Corporation

Document 600065 Rev 04
spikes of current into C
audio signal input to the RMS detector increases
suddenly. This current is drawn from V
fed through C
supply through the ground end of C
dled properly through layout and bypassing, these
currents can mix with the audio with unpredictable
and undesirable results. As noted in the Applica-
tions section, local bypassing from the V
ground end of C
der to keep these currents out of the ground struc-
ture of the device.
same constant of proportionality as the VCA gain
control: 6.0 mV/dB. The detector’s 0 dB reference
(i
output to equal V
probe to approximately equal 7.5 mA. The RMS de-
tector output stage is capable of sinking or sourcing
125 mA. It is also capable of driving up to 150 pF of
capacitance.
across the audio band for a wide range of input sig-
nal levels. Note, however, that it does fall off at high
frequencies at low signal levels.
tor circuitry and that of the THAT 2252 RMS Detec-
tor include the following.
ternally balanced by design, and cannot be balanced
via an external control. The 4315 will typically bal-
ance positive and negative halves of the input signal
within 10 %, but in extreme cases the mismatch may
reach +40, -30 % (±3 dB). However, even such ex-
treme-sounding mismatches will not significantly in-
crease
processors over that caused by signal ripple alone.
is determined by the combination of an external ca-
pacitor (connected to the C
current source. The internal current source is set to
about 7.5 mA. A resistor is not normally connected
directly to the C
also set to approximately 7.5 mA. However, as in the
2252, the level match will be affected by any addi-
tional currents drawn from the C
in0
The RMS detector is capable of driving large
The dc output of the detector is scaled with the
Frequency response of the detector extends
Differences between the 4315’s RMS Level Detec-
1. The rectifier in the 4315 RMS Detector is in-
2. The time constant of the 4315’s RMS detector
3. The 0 dB reference point, or level match, is
, the input current which causes the detector’s
ripple-induced
TIME
T
TIME
pin on the 4315.
at pin 4, and returns to the power
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
REF
is strongly recommended in or-
), is trimmed during wafer
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
TIME
distortion
, particularly when the
T
pin) and an internal
T
pin.
TIME
in
Copyright © 2009, THAT Corporation
. If not han-
CC
CC
pin to the
dynamics
(pin 9),
V
a center-tap to provide a synthetic “ground” refer-
ence for its circuitry. The 4315 contains a built-in
resistive divider (at pins 7, 8 and 9), but unlike the
THAT4320, this voltage is unbuffered. Note that the
center tap of the resistive divider is brought out to
filter the voltage, thereby minimizing noise in the di-
vider. A large electrolytic capacitor (typically 22 mF
or greater) is used for this purpose. In cases where
users expect to dump significant current onto V
the user should add an op-amp to provide a
low-impedance source at approximately half V
rectly to the unbuffered V
shifts of up to +/-900 mV in the reference voltage
due to DC currents flowing in or out of this pin as a
result of the internal VCA symmetry trim. In such
cases, buffering of the V
ommended. As an alternative, a lower impedance
external voltage divider can be substituted (2 kW re-
sistors will limit any variation in V
100 mV).
cuit ground (GND); V
to relatively high impedance loads (e.g., the positive
input of opamps). Where significant currents (signal
or otherwise) must be delivered at the V
an opamp should be used to buffer the V
self.
is to operate the 4315 from symmetrical split sup-
plies (e.g. ±5 V and ground). In such cases, the cen-
ter-tap of the resistive divider (pin 7) should be
grounded. This will force V
offset of the V
Noise Reduction (Compander)
Configurations
systems, particularly within battery-operated de-
vices. In these applications, one 4315 is configured
for use as a compressor to condition audio signals
before feeding them into a noisy channel. A second
4315, configured as an expander, is located at the
receiver end of the noisy channel. The compressor
increases gain in the presence of low-level audio sig-
nals, and reduces its gain in the presence of
high-level audio signals. The expander works in op-
posite, complementary fashion to restore the origi-
CC
For single-supply applications, the 4315 requires
Connecting the postive control port, Ec+, di-
Any signal currents should return to the real cir-
Another approach to power supply arrangements
A primary use of the 4315 is for noise reduction
/2 Reference Buffer
CC
/2 buffer.
REF
CC
CC
/2 reference voltage is rec-
should be connected only
/2 reference can result in
REF
to ground within the
CC
/2 to less than
REF
REF
dc level,
CC
line it-
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