that4320 THAT Corporation, that4320 Datasheet - Page 9

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

Document 600045 Rev 04
solving signals well below 10 mV (with a 5 kΩ input
resistor). However, if the detector is to accurately
track such low-level signals, ac coupling is normally
required (C
low-voltage electrolytic capacitors used for this pur-
pose may create significant leakage if they support half
the supply voltage, as is the case when the source is
dc-referenced to ground. To ensure good detector
tracking to low levels, a tantalum capacitor or
high-voltage electrolytic may be required for input
coupling.
placed well below the frequency range of interest.
For an audio-band detector, a typical value would be
5 Hz, or a 32 ms time constant (τ). The filter’s time
constant is determined by an external capacitor
C
source (I
ternally fixed at 7.5 μA. The resulting time constant
in seconds is approximately equal to 3467 * C
Note that, as a result of the mathematics of RMS de-
tection, the attack and release time constants are
fixed in their relationship to each other.
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. See figure 10 [page 7]. The de-
tector’s 0 dB reference (i
causes the detector’s output to equal V
trimmed during wafer probe to approximately equal
7.5 μA. The RMS detector output stage is capable of
sinking or sourcing 125 μA.
driving up to 150 pF of capacitance.
the audio band for a wide range of input signal levels.
Note, however, that it does fall off at high frequencies
at low signal levels. See figure 11 (page 7).
tor circuitry and that of the THAT 2252 RMS Detec-
tor include the following.
ternally balanced by design, and cannot be balanced
TIME
7
THAT has applied for patent coverage on this novel approach.
The log-domain filter cutoff frequency is usually
The RMS detector is capable of driving large
The dc output of the detector is scaled with the
Frequency response of the detector extends across
Differences between the 4320’s RMS Level Detec-
1) The rectifier in the 4320 RMS Detector is in-
attached to the C
T
) connected to C
27
TIME
in Figure 2).
TIME
at pin 7, and returns to the power
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
is strongly recommended in or-
T
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
pin, and an internal current
TIME
in0
T
. The current source is in-
, the input current which
, particularly when the
Note also that small,
It is also capable of
TIME
Copyright © 2007, THAT Corporation
. If not han-
CC
CC
pin to the
(pin 15),
REF
TIME
), is
.
via an external control. The 4320 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 μA. A resistor is not normally connected
directly to the C
also set to approximately 7.5 μA. However, as in the
2252, the level match will be affected by any addi-
tional currents drawn from the C
The Opamps — in Brief
mized independently to suit each one’s intended ap-
plication. While they all use PNP input stages, they
differ in bandwidth, noise level, and compensation
scheme depending on their expected uses. There-
fore, to get the most out of the 4301, it is useful to
know the major differences among these opamps.
OA
4.5 nV/ÖHz, is the quietest opamp on the 4320. This
opamp is intended for signal conditioning such as
preamplification from low-impedance sources. (At
source impedances of >5.6 kΩ, the input current noise
contribution will surpass the voltage contribution.)
ances at both inputs less than ~ 5 kΩ, 13 MHz
opamp . Its output typically swings to within 0.75 V
of V
wave from a single +5 V supply (4.75 V
+15 V supply). Its typical slew rate is ~ 4 V/μs, al-
lowing the part to support maximum level sine
waves at up to 360 kHz on a +5V supply (94 kHz on
a +15 V supply). OA
up to 150 pF, so it is possible to directly bypass RF
to ground via a small capacitor at OA
often desired in wireless transmitter applications.
power supply connection is brought out separately
to V
certain applications. While V
nected to the power supply ground (and pins 1 and
14, which are the ground connections for the rest of
the chip), it can be connected to a separate negative
supply. OA
connected to V
2) The time constant of the 4320’s RMS detector
3) The 0 dB reference point, or level match, is
The four opamps in the 4320 have been opti-
1
OA
OA
OA
CC
EE
- Low Source Impedance Pre-amp
1
1
1
or V
,
‘s most unusual feature
(pin 28) to provide additional headroom in
is a unity-gain stable, with source imped-
ripple-induced
with
1
EE
‘s positive supply connection is internally
, allowing it to support a 1.2 V
CC
T
typical
pin on the 4320.
(pin 15). Therefore, OA
1
‘s output is capable of driving
equivalent
distortion
T
pin) and an internal
EE
7
T
is that it’s negative
pin.
is normally con-
input
1
‘s output, as is
in
RMS
dynamics
1
noise
RMS
sees as
with a
Page 9
sine
of