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PDF THAT4305 Data sheet ( Hoja de datos )
| Número de pieza | THAT4305 | |
| Descripción | Analog Engine | |
| Fabricantes | THAT Corporation | |
| Logotipo |  |
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T H AT Corporation
FEATURES
· Pre-trimmed Blackmer™ VCA &
RMS-level detector
· Wide supply voltage range:
±4.5V ~±16V
· Low supply current:
3.5 mA typ. (±15V)
· Wide dynamic range:
117 dB (VCA)
60 dB (RMS-level detector)
Pre-trimmed Analog Engine® IC
THAT 4305
APPLICATIONS
· Compressors & Limiters
· Gates & Expanders
· AGCs
· Line-operated dynamics processors
· De-Essers
· Duckers
· Mixers
· Level indicators
· Companding noise reduction systems
Description
The THAT4305 is a single-chip Analog En-
The 4305 was developed specifically for use
gine optimized for low-cost applications. It incor-
in low-cost dynamics processors, drawing from
porates a high-performance Blackmer voltage-
THAT's long history and experience with such
controlled amplifier (VCA) and log-responding
designs. Both VCA control ports and the detec-
RMS-level sensor. The VCA and RMS detector
tor input and output are available for the de-
are pre-trimmed at wafer stage to deliver low dis-
signer to connect as s/he sees fit. As a result, the
tortion without further adjustment.
part is extremely flexible and can be configured
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iters, gates, and other dynamic processors. The
cators, etc.
part normally operates from a split supply volt-
What really sets the 4305 apart from other
age up to ±16Vdc, drawing only 3.5mA at ±15V.
manufacturers’ offerings is the transparent sound
This IC also works at supply voltages as low as
of its Blackmer VCA, coupled with its accurate
±4.5V, making it useful in some battery-operated
true-RMS level detector. This makes the IC useful
products as well.
in a wide range of analog audio products.
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VCA
VCA
NC IN NC OUT EC- EC+ NC VCC
16 15 14 13 12 11 10 9
VCA
IN OUT
EC+ EC-
RMS
IN OUT
CT
123
NC RMS NC
IN
45678
CT RMS GND NC VEE
OUT
Figure 1. THAT4305 equivalent block diagram
Pin Name
No Connection
RMS IN
No Connection
CTIME
RMS OUT
GND
NC
Vee
VCC
No Connection
EC+
EC-
VCA OUT
No Connection
VCA IN
No Connection
Pin Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Table 1. THAT 4305 pin assignments
Package
16 pin QSOP
Order Number
4305Q16-U
Table 2. Ordering Information
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
Document 600067 Rev 00
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Document 600067 Rev 00
Page 5
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The rectifier is balanced to within ±3 dB, so a
(iin0, the input current which causes the detector's
small amount of fundamental (and higher odd-order
output to equal 0V), is trimmed during wafer probe
harmonics) ripple can be present at the detector out-
to equal approximately 7.5 µA. The RMS detector
put. By design, this ripple contributes less total rip-
output stage is capable of sinking or sourcing
ple than the even-order products that are naturally
125 µA. It is also capable of driving up to 150 pF of
and inevitably present at the output of a perfectly
capacitance.
balanced detector.
Frequency response of the detector extends
As in the VCA, input signals are currents to the
across the audio band for a wide range of input sig-
RMSIN pin (pin 2). This input is a virtual ground, so
nal levels. Note, however, that it does fall off at high
a resistor (R1 in Figure 2) is normally used to con-
frequencies at low signal levels like THAT’s other
vert input voltages to the desired current. The level
RMS detectors.
detector is capable of accurately resolving signals
well below 10 mV (with a 5 kΩ input resistor). How-
ever, if the detector is to accurately track such
low-level signals, ac coupling (C1 in Figure 2) is re-
Differences between the 4305's RMS level
detector circuitry and that of the THAT 2252 RMS
detector include the following.
quired to prevent dc offsets from causing a dc cur-
1. The rectifier in the 4305 RMS Detector is in-
rent to flow in the detector’s input, which would
ternally balanced by design, and cannot be balanced
obscure low-level ac signal currents.
via an external control. The 4305 will typically bal-
ance positive and negative halves of the input signal
The log-domain filter cutoff frequency is usually
within 10 %, but in extreme cases the mismatch may
placed well below the frequency range of interest.
reach +40 % or -30 % (±3 dB). However, even such
For an audio-band detector, a typical value would be
extreme-seeming mismatches will not significantly
5 Hz, or a 32 ms time constant (τ). The filter's time
increase ripple-induced distortion in dynamics pro-
constant is determined by an external timing capaci-
cessors over that caused by balanced signal ripple
tor (CTIME) attached to the CT pin (pin 4), and aDnaitna-Sheet4Ua.cloonme.
ternal current source (IT) connected to CT. The
current source is internally fixed at 7.5 µA. The re-
2. The time constant of the 4305's RMS detector
sulting time constant in seconds is approximately
is determined by the combination of an external ca-
equal to 3467 times the value of the timing capacitor
pacitor CTIME and an internal current source. The in-
in Farads. Note that, as a result of the mathematics
ternal current source is set to about 7.5 µA. A
of RMS detection, the attack and release time con-
resistor is not normally connected directly to the CT
stants are fixed in their relationship to each other.
pin on the 4305.
The RMS detector is capable of driving large
spikes of current into CTIME, particularly when the
audio signal input to the RMS detector increases
suddenly. This current is drawn from VCC (pin 9),
fed through CTIME at pin 4, and returns to the power
supply through the ground end of CTIME. If not han-
dled properly through layout and bypassing, these
currents can mix with the audio in the circuit’s
ground structure with unpredictable and undesir-
able results. As noted in the Applications section,
local bypassing from the VCC pin to the ground end
of CTIME is strongly recommended in order to keep
these currents out of the ground structure of the cir-
cuit (see C4 in Figure 2.)
The dc output of the detector is scaled with the
same constant of proportionality as the VCA gain
control: 6.2 mV/dB. The detector's 0 dB reference
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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 addi-
tional currents drawn from the CT pin.
Compressor (or Limiter) Configurations
The 4305 provides the two essential building
blocks required for a wide variety of dynamics pro-
cessing applications. The part may be configured
into practically any type of dynamics processor sys-
tem.
Perhaps the most common application for the
4305 is as a compressor or limiter. These circuits
are intended to reduce gain above some determined
signal level in order to prevent subsequent stages
from being overloaded by too high a signal. Com-
pressors generally have low to moderate compres-
DataSheet4 U .com
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
DataSheet4U.com
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Document 600067 Rev 00
Page 11
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slightly with temperature unless the applied voltage
is appropriately compensated.
If we let TdB=20, AdB=0 dB, and k=0.75, this be-
havior yields the transfer function shown in Fig-
ure 13. As predicted by the above equations, this
results in a 4:1 compression ratio above the thresh-
old of -20 dB (relative to the RMS detector's 0 dB
reference level. The output level increases by 10 dB
over a 40 dB change in input level.
20
10
0
-10
-20
-30
-40 Out
-50 In
-60
-70
-80
-90
-100
-100 -80 -60 -40 -20
0
dB In
20
ment (AdB) just as in Figure 8. However, in this
case, the detector level is based on the compressor’s
output.
Once again we start with
OutdB = IndB + GdB
For output signals above the level determined by
the threshold setting,
OutdB > TdB .
So for signals above the threshold,
GdB = −k(OutdB − TdB) + AdB .
Substituting yields
OutdB = IndB − k(OutdB − TdB) + AdB ,
which can be reduced to
OutdB
=
IndB + TdB + AdB
(1+ k)
.
For output signals below the level set by the
threshold setting, the signal at the output of the
ideal diode threshold is 0 (dB), so
Figure 13. Transfer function of a feedforward compressor
GdB = AdB , and
DataSheet4U.coOmutdB = IndB + AdB
In Figure 14, we have again extended the basic
feedback compressor with a threshold adjustment
(TdB), a threshold (the ideal diode), a means to vary
the sidechain gain (k), and a make-up gain adjust-
If we let TdB=10, AdB=20, and k=10, this behav-
ior yields the transfer function shown in Figure 15.
The compression ratio of 11:1 allows a rise of only
about 4.5 dB over a 50 dB range.
DataShee
IndB
GdB
S
A dB
Out dB
RMS
Ideal
Diode
Out dB
-k S +
-
TdB
Figure 14. Feedback compressor with threshold, gain, and
ratio adjustments
0
-50 Out
In
-100
-100
-50
dB Out
0
Figure 15. Transfer function of a feedback compressor
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THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: +1 508 478 9200; Fax: +1 508 478 0990; Web: www.thatcorp.com
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| PDF Descargar | [ Datasheet THAT4305.PDF ] | |
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