Pre-trimmed Low-voltage
Low-power Analog Engine® IC
THAT
4315
FEATURES
• Pre-trimmed VCA & RMS detector
• Wide supply voltage range: 4.5V~16V
• Low supply current: 1.6 mA typ. (5V)
• Wide dynamic range: 118 dB as
compander
APPLICATIONS
• Companding noise reduction
• Wireless microphones
• Wireless instrument packs
• Wireless in-ear monitors
• Battery operated dynamics processors
• Compressors
• Limiters
• AGCs
• De-essers
Description
The THAT4315 is a single-chip Analog Engine®
optimized for low-voltage, low-power operation.
Incorporating a high-performance voltage-controlled
amplifier (VCA) and RMS-level sensor, the surface
mount part is aimed at battery-operated audio appli-
cations such as wireless microphones, wireless
instruments and in-ear monitors. The 4315 operates
from a single supply voltage down to +4.5Vdc,
drawing only 1.6mA.
This IC also works at supply voltages up to
16Vdc, making it useful in line-operated products as
well. The VCA is pre-trimmed at wafer stage to
deliver low distortion without further adjustment.
The part was developed specifically for use as a
companding noise reduction system, drawing from
THAT’s long history and experience with dbx®
technology for noise reduction. However, with 11
active pins, the part is extremely flexible and can be
configured for a wide range of applications including
single and multi-band companders, compressors,
limiters, AGCs, de-essers, etc.
What really sets the 4315 apart is the transpar-
ent sound of its Blackmer® VCA coupled with its
accurate true-RMS level detector. The I
C is useful
in battery-powered mixers, compressor/limiters,
ENG devices and other portable audio products.
NC
VCA
IN
NC
VCA
OUT
EC-
EC+
NC
VCC
16
15
14
13
12
11
10
9
IN
VCA
OUT
EC+ EC-
Ra
THAT
4315
IN
RMS
OUT
CT
Rb
1
NC
2
RMS
IN
3
NC
4
CT
5
RMS
OUT
6
VREF
7
FILT
8
GND
Figure 1. THAT4315 equivalent block diagram
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Email: info@thatcorp.com; Web: www.thatcorp.com
Copyright © 2011, THAT Corporation; Document 600065 Rev 05
Document 600065 Rev 05
Page 2 of 13
THAT4315 Pre-trimmed Low-voltage
Low-power Analog Engine® IC
SPECIFICATIONS
1
Absolute Maximum Ratings
2
Positive Supply Voltage (V
CC
)
Supply Current (I
CC
)
Operating Temperature Range (T
OP
)
Junction Temperature (T
J
)
Output Short-Circuit Duration
+18V
30mA
-40 to +85 ºC
-40 to +125 ºC
30 sec
Power Dissipation (P
D
) at T
A
=85 ºC
400mW
Input Voltage
Supply Voltage
-40 to +125 ºC
Storage Temperature Range (T
ST
)
Lead Temperature Range (Soldering, 10 sec)
300 ºC
Electrical Characteristics
3
Parameter
Power Supply
Positive Supply Voltage
Supply Current
V
CC
I
CC
Referenced to GND
No Signal
V
CC
=+5 V
V
CC
=+15 V
Voltage Controlled Amplifier (VCA)
Max. I/O Signal Current
i
IN(VCA)
+ i
OUT(VCA)
V
CC
= +5 V
V
CC
= +15 V
VCA Gain Range
Gain at 0V Control
Gain-Control Constant
Gain-Control Tempco
G
0
E
C+
/Gain (dB)
∆E
C
/∆T
CHIP
E
C+
= E
C-
= 0V
-40 dB to +40 dB
Ref T
CHIP
=27ºC
R
OUT
= 20 kΩ
0 dB gain
+15 dB gain
+30 dB gain
Output Noise
e
N(OUT)
0 dB gain
22Hz~22kHz, R
IN
=R
OUT
=20 kΩ
Total Harmonic Distortion
RMS Level Detector
Output Voltage at Reference i
IN
e
O(0)
i
IN
= 7.5
μA
RMS
i
IN
= 200 nA RMS
i
IN
= 1
μA
RMS
Scale Factor Match to VCA
-20 dB < VCA gain < +20 dB
1
μA<
i
IN(RMS)
< 100 µ A
Rectifier Balance
±7.5
μA
DC
IN
.95
1
±1
1.05
—
dB
-9
—
—
0
1
1
+9
3
3
mV
dB
dB
THD
V
IN
= -5dBV, 1kHz, E
C+
= E
C-
= 0V
—
—
-98
0.07
-95
0.15
dBV
%
—
—
—
1
3
10
15
30
50
mV
mV
mV
—
—
-50
-1.0
—
—
500
1
—
0
6.0
+0.33
—
—
+50
+1.0
—
—
µA
peak
mA
peak
dB
dB
mV/dB
%/ºC
—
—
1.6
2.3
2.5
3.5
mA
mA
+4.5
—
+16
V
Symbol
Conditions
Min
Typ
Max
Units
Output Offset Voltage Change
4
∆
V
OFF(OUT)
Output Error at Input Extremes e
O(RMS)error
1. All specifications are subject to change without notice.
2. If the devices are subjected to stress above the Absolute Maximum Ratings, permanent damage may result. Sustained operation at or near the Absolute
Maximum Ratings conditions is not recommended. In particular, like all semiconductor devices, device reliability declines as operating temperature increases.
3. Unless otherwise noted, T
A
=25ºC, V
CC
=+5V, V
EE
=0 V.
4. Reference is to output offset with -80 dB VCA gain.
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Email: info@thatcorp.com; Web: www.thatcorp.com
Copyright © 2011, THAT Corporation
Document 600065 Rev 05
Page 3 of 13
THAT4315 Pre-trimmed Low-voltage
Low-power Analog Engine® IC
Electrical Characteristics (con’t)
3
Parameter
Timing Current
Filtering Time Constant
Output Tempco
Load Resistance
Capacitive Load
V
CC
/2 Reference Divider
Reference Voltage
V
REF
No Signal, No load on pin 7
V
CC
= +5 V
V
CC
= +15 V
Voltage Divider Impedance
R
A
, R
B
2.4
—
—
2.5
V
CC
/2
20
2.6
—
—
V
V
kΩ
Symbol
I
T
τ
∆E
O
/∆T
CHIP
R
L
C
L
T
CHIP
= 27 ºC
Ref T
CHIP
= 27 ºC
-250mV < V
OUTRMS
< +250mV, re:Vref
—
2
—
Conditions
Min
—
Typ
7.5
3467 X C
TIME
+0.33
—
—
—
—
150
Max
—
Units
µA
s
%/ºC
kΩ
pF
Performance as a Compander (through an encode-decode cycle)
Dynamic Range
Distortion
Frequency response
THD
-20 dB re: Max Signal
(max signal level)-(no signal output noise)
f = 1 kHz
20 Hz ~ 20 kHz
—
—
—
120
0.15
± 1.5
—
—
—
dB
%
dB
Package Characteristics
Parameter
Surface Mount Package
Type
Thermal Resistance
Thermal Resistance
Soldering Reflow Profile
θ
JC
θ
JA
See page 12 for pinout and dimensions
SO package in ambient
SO package soldered to board
16 pin QSOP
TBD
TBD
ºC/W
ºC/W
Symbol
Conditions
Typ
Units
JEDEC JESD22-A113-B (220 ºC)
Theory of Operation
The THAT 4315 Dynamics Processor combines
THAT Corporation’s proven Voltage-Controlled
Amplifier (VCA) and an RMS-Level Detector in a
package optimized for low cost circuits. The part is
integrated using a proprietary, fully complementary,
dielectric-isolation process. This process produces
very high-quality bipolar transistors (both NPNs and
PNPs) with unusually low collector-substrate capaci-
tances. The 4315 takes advantage of these devices to
deliver wide bandwidth and excellent audio perform-
ance while consuming very low current and operating
over a wide range of power supply voltages.
For details of the theory of operation of the VCA
and RMS Detector building blocks, the interested
reader is referred to THAT Corporation’s data sheets
on the 2180-Series VCAs and the 2252 RMS Level
Detector. Theory of the interconnection of
exponentially-controlled VCAs and log-responding
level detectors is covered in THAT Corporation’s
design note DN01A,
The Mathematics of Log-Based
Dynamic Processors.
The VCA — in Brief
The VCA in THAT 4315 is based on THAT Corpo-
ration’s highly successful complementary log-antilog
gain cell topology — The Blackmer® VCA— as used
in THAT 2180-Series IC VCAs. VCA symmetry is
trimmed during wafer probe for minimum
distortion. No external adjustment is allowed.
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Email: info@thatcorp.com; Web: www.thatcorp.com
Copyright © 2011, THAT Corporation
Document 600065 Rev 05
Page 4 of 13
THAT4315 Pre-trimmed Low-voltage
Low-power Analog Engine® IC
Input signals are currents in the VCA’s IN pin.
This pin is a virtual ground with dc level approxi-
mately equal to V
REF
, so in normal operation an input
voltage is converted to input current via an appropri-
ately sized resistor. Because the currents associated
with dc offsets present at the input pin and any dc
offset in preceding stages will be modulated by gain
changes (thereby becoming audible as thumps), the
input pin is normally ac-coupled.
The VCA output signal is also a current, inverted
with respect to the input current. In normal opera-
tion, the output current is converted to a voltage via
external op-amp, where the ratio of the conversion is
determined by the feedback resistor connected
between op-amp‘s output and its inverting input. The
signal path through the VCA and op-amp is
noninverting.
The gain of the VCA is controlled by the voltage
applied between EC+ and EC-. Note that any unused
control port should be connected to the V
REF
genera-
tor. The gain (in decibels) is proportional to (EC+ –
EC-). The constant of proportionality is 6.0 mV/dB
for the voltage at EC+ (relative to EC-), but note that
neither EC+ or EC- should vary more than ±0.5 V
from V
REF
.
The VCA’s noise performance varies with gain in
a predictable way, but due to the way internal bias
currents vary with gain, noise at the output is not
strictly the product of a static input noise times the
voltage gain commanded. At large attenuation, the
noise floor of ~ -109 dBV is limited by the input
noise of the output op-amp and its feedback resistor.
At 0 dB gain, the noise floor is ~ -98 dBV as speci-
fied. In the vicinity of 0 dB gain, the noise increases
more slowly than the gain: approximately 5 dB noise
increase for every 10 dB gain increase. Finally, as
gain approaches 30 dB, output noise begins to
increase directly with gain.
While the 4315’s VCA circuitry is very similar to
that of the THAT 2180 Series VCAs, there are several
important differences, as follows:
1. Supply current for the VCA depends on V
CC
. At
+5 V V
CC
, approximately 500
μA
is available for the
sum of input and output signal currents. This
increases to about 1 mA at +15 V V
CC
. (Compare this
to ~1.8 mA for a 2180 Series VCA when biased as
recommended. This is appropriate given the lower
supply voltage for the 4315.)
2. A SYM control port (similar to that on the
2180 VCA) exists, but is driven from an internally
trimmed current generator.
3. The control-voltage constant is approximately
6.0 mV/dB, due primarily to the lower internal
operating temperature of the 4315 compared to that
of the 2180 Series (and the 4301).
4. The OTA used for the VCA’s internal opamp in
the 4315 uses less emitter degeneration resistance in
its output than that of the 2180 VCA. This requires
that the source impedance at the VCA’s input (which
is a summing junction) must be under 5 kΩ at
frequencies over 1 MHz. See the applications section
for an alternative on how to address this issue.
The RMS Detector — in Brief
The 4315’s detector computes RMS level by recti-
fying input current signals, converting the rectified
current to a logarithmic voltage, and applying that
voltage to a log-domain filter. The output signal is a
dc voltage proportional to the decibel-level of the
RMS value of the input signal current. Some ac
component (at twice the input frequency) remains
superimposed on the dc output. The ac signal is
attenuated by a log-domain filter, which constitutes a
single-pole rolloff with cutoff determined by an exter-
nal capacitor.
As in the VCA, input signals are currents to the
RMS
IN
pin. This input is a virtual ground with dc
level equal to V
REF
, so a resistor, R24 in Figure 2, is
normally used to convert input voltages to the
desired current. The level detector is capable of
accurately resolving 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
required. Note also that small, low-voltage electro-
lytic capacitors used for this purpose 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 high quality electrolytic may
be required for input coupling.
The log-domain filter cutoff frequency is usually
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 timing capaci-
tor attached to the C
T
pin, and an internal current
source (I
T
) connected to C
T
. The current source is
internally fixed at 7.5
μA.
The resulting time constant
in seconds is approximately equal to 3467 times the
value of the timing capacitor. Note that, as a result of
the mathematics of RMS detection, the attack and
release time constants are fixed in their relationship
to each other.
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Email: info@thatcorp.com; Web: www.thatcorp.com
Copyright © 2011, THAT Corporation
Document 600065 Rev 05
Page 5 of 13
THAT4315 Pre-trimmed Low-voltage
Low-power Analog Engine® IC
The RMS detector is capable of driving large
spikes of current into C
TIME
, particularly when the
audio signal input to the RMS detector increases
suddenly. This current is drawn from V
CC
(pin 9),
fed through C
TIME
at pin 4, and returns to the power
supply through the ground end of C
TIME
. If not
handled properly through layout and bypassing,
these currents can mix with the audio with unpre-
dictable and undesirable results. As noted in the
Applications section, local bypassing from the V
CC
pin
to the ground end of C
TIME
is strongly recommended
in order to keep these currents out of the ground
structure of the device.
The dc output of the detector is scaled with the
same constant of proportionality as the VCA gain
control: 6.0 mV/dB. The detector’s 0 dB reference
(i
in0
, the input current which causes the detector’s
output to equal V
REF
), is trimmed during wafer probe
to approximately equal 7.5
μA.
The RMS detector
output stage is capable of sinking or sourcing
125
μA.
It is also capable of driving up to 150 pF of
capacitance.
Frequency response of the detector extends
across 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.
Differences between the 4315’s RMS Level Detec-
tor circuitry and that of the THAT 2252 RMS Detec-
tor include the following.
1. The rectifier in the 4315 RMS Detector is inter-
nally balanced by design, and cannot be balanced via
an external control. The 4315 will typically balance
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 extreme-
sounding mismatches will not significantly increase
ripple-induced distortion in dynamics processors
over that caused by signal ripple alone.
2. The time constant of the 4315’s RMS detector
is determined by the combination of an external
capacitor (connected to the C
T
pin) and an internal
current source. The internal current source is set to
about 7.5
μA.
A resistor is not normally connected
directly to the C
T
pin on the 4315.
3. The 0 dB reference point, or level match, is
also set to approximately 7.5
μA.
However, as in the
2252, the level match will be affected by any
additional currents drawn from the C
T
pin.
V
CC
/2 Reference Buffer
For single-supply applications, the 4315 requires
a center-tap to provide a synthetic “ground” reference
for its circuitry. The 4315 contains a built-in resis-
tive 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
divider. A large electrolytic capacitor (typically 22
μF
or greater) is used for this purpose. In cases where
users expect to dump significant current onto V
REF
,
the user should add an op-amp to provide a
low-impedance source at approximately half V
CC
.
Connecting the postive control port, Ec+, directly
to the unbuffered V
CC
/2 reference can result in 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
CC
/2 reference voltage is recom-
mended. As an alternative, a lower impedance exter-
nal voltage divider can be substituted (2 kΩ
resistors will limit any variation in V
CC
/2 to less than
100 mV).
Any signal currents should return to the real
circuit ground (GND); V
REF
should be connected only
to relatively high impedance loads (e.g., the positive
input of opamps). Where significant currents (signal
or otherwise) must be delivered at the V
REF
dc level,
an opamp should be used to buffer the V
REF
line
itself.
Another approach to power supply arrangements
is to operate the 4315 from symmetrical split
supplies (e.g. ±5 V and ground). In such cases, the
center-tap of the resistive divider (pin 7) should be
grounded. This will force V
REF
to ground within the
offset of the V
CC
/2 buffer.
Noise Reduction (Compander)
Configurations
A primary use of the 4315 is for noise reduction
systems, particularly within battery-operated devices.
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 signals, and
reduces its gain in the presence of high-level audio
signals. The expander works in opposite, comple-
mentary fashion to restore the original signal levels
present at the input of the compressor.
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Email: info@thatcorp.com; Web: www.thatcorp.com
Copyright © 2011, THAT Corporation
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