LM832 [NSC]
LM832 Dynamic Noise Reduction System DNR; LM832动态降噪系统DNR
| 型号： | LM832 |
| 厂家： | 
National Semiconductor |
| 描述： | LM832 Dynamic Noise Reduction System DNR |
| 文件： | 总11页 (文件大小：229K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
August 1989
LM832 Dynamic Noise Reduction System DNR
É
General Description
Features
Y
Low voltage battery operation
The LM832 is a stereo noise reduction circuit for use with
audio playback systems. The DNR system is noncomple-
mentary, meaning it does not require encoded source mate-
rial. The system is compatible with virtually all prerecorded
tapes and FM broadcasts. Psychoacoustic masking, and an
adaptive bandwidth scheme allow the DNR to achieve 10
dB of noise reduction. DNR can save circuit board space
and cost because of the few additional components re-
quired.
Y
Non-complementary noise reduction, ‘‘single ended’’
Low cost external components, no critical matching
Compatible with all prerecorded tapes and FM
10 dB effective tape noise reduction CCIR/ARM
weighted
Y
Y
Y
Y
Y
Y
Y
Wide supply range, 1.5V to 9V
150 mVrms input overload
No royalty requirements
The LM832 is optimized for low voltage operation with input
levels around 30 mVrms.
Cascade connection for 17 dB noise reduction
For higher input levels use the LM1894.
Applications
Y
Headphone stereo
Y
Microcassette players
DNRÉ is a registered trademark of National Semiconductor Corporation.
The DNRÉ system is licensed to National Semiconductor Corp. under U.S. patent 3,678,416
Y
Radio cassette players
and 3,753,159.
A trademark and licensing agreement is required for the use of this product.
Y
Automotive radio/tape players
Order Number LM832M See NS Package M14A
Order Number LM832N See NS Package N14A
Application Circuit
TL/H/5176–1
FIGURE 1. Component Hook-up for Stereo DNR System
C
1995 National Semiconductor Corporation
TL/H/5176
RRD-B30M115/Printed in U. S. A.
Absolute Maximum Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Soldering Information
Y
Dual-In-Line Package
Soldering (10 seconds)
260 C
§
Supply Voltage
10V
1.2W
Y
Small Outline Package
Power Dissipation (Note 1)
Input Voltage
Vapor Phase (60 seconds)
Infrared (15 seconds)
215 C
§
220 C
§
1.7 Vpp
b
a
65 to 150 C
Storage Temperature
Operating Temperature (Note 1)
§
40 to 85
See AN-450 ‘‘Surface Mounting Methods and Their Effects
on Products Reliability’’ for other methods of soldering sur-
face mount devices.’’
b
a
§
e
e
3.0V
DC Electrical Characteristics T
25 C V
§
A
CC
Conditions
Supply Voltage for Normal Operation
Symbol
Parameter
Min
Typ
3.0
Max
9.0
Units
V
V
Operating Voltage
Supply Current (1)
Supply Current (2)
Input Voltage (1)
Input Voltage (2)
Input Voltage (3)
Output Voltage (1)
Output Voltage (2)
Output Voltage (3)
Output Voltage (4)
Output Voltage (5)
Output Voltage (6)
Output DC Shift
1.5
OP
e
I
I
(1)
Pin 9 to GND 0.1 mF, BW Min, Note 2
2.5
4.0
mA
mA
V
CC
CC
e
DC GND Pin 9 with 2k, BW Max, Note 2
(2)
5.0
8.0
V
V
V
V
V
V
V
V
V
V
(1)
(2)
(3)
Pin 2, Pin 13
0.20
0.50
0.50
0.20
0.15
0.10
0.25
1.00
0.50
0.36
0.65
0.65
0.35
0.28
0.20
0.40
1.27
0.65
1.0
0.5
IN
IN
IN
Pin 6
0.8
V
Pin 9
0.8
V
(1)
Pin 4, Pin 11
0.50
0.40
0.30
0.60
1.50
0.75
3.0
V
OUT
OUT
OUT
OUT
OUT
OUT
OS
(2)
(3)
(4)
(5)
(6)
Pin 5 Stereo Mode
V
Pin 5 Monaural Mode, DC Ground Pin 14
Pin 8
V
V
e
Pin 10 BW Max, Note 2
V
e
Pin 10 BW Min, Note 2
V
Pin 4, PIN 11; Change BW Min to Max
mV
AC Electrical Characteristics
Symbol
Parameter
Conditions
Min
Typ
Max
Units
MAIN SIGNAL PATH (Note 3)
e
e
e
e
30 mVrms, f 1 kHz, BW Max, Note 2
b
a
a
A
Voltage Gain
V
V
1.0
1.0
0.0
0
1.0
1.0
dB
dB
V
IN
e e
30 mVrms, f 1 kHz, BW Max, Note 2
b
C.B.
Channel Balance
Min Bandwidth
Max Bandwidth
Distortion
IN
f
f
0.1 mF between Pin 9 - GND
600
24
1000
30
1500
46
Hz
MIN
DC Ground Pin 9 with 2k
kHz
%
MAX
e
e
e
30 mVrms, f 1 kHz, BW Max, Note 2
THD
V
IN
0.07
150
68
0.5
e
e
e
THD 3%, f 1 kHz, BW Max Note 2
MV
Max Input Voltage
Signal to Noise
Input Impedance
Channel Separation
120
60
mVrms
dB
IN
e
e
S/N
REF 30 mVrms, BW Max, CCIR/ARM
Pin 2, Pin 13
Z
IN
14
20
26
kX
e
e
e
Ref 30 mVrms, f 1 kHz, BW Max, Note 2
C.S.
40
68
dB
e
RIPPLE
e
50 mVrms, f 100 Hz
P
P
V
40
55
dB
SRR
CONTROL PATH
A sum(1)
SRR
e
V
IN
e
30 mVrms at R and L, f 1 kHz
b
b
b
Summing Amp Gain (1)
Summing Amp Gain (2)
Gain Amp Gain
3.0
9.0
1.5
6.0
0.0
dB
dB
dB
kX
V/V
X
V
e
b
b
3.0
35
A sum(2)
V
DC Ground Pin 14, f 1 kHz
Pin 6 to Pin 8
A
1st
1st
25
30
V
Z
IN
Input Impedance
Pin 6
28
25
40
30
52
35
A
Peak Detector Gain
Input Impedance
AC In, DC Out; Pin 9 to Pin 10
Pin 9
VPKD
INPKD
RPKD
Z
V
500
0.5
800
0.62
1100
0.8
Output DC Change
Pin 10, Change BW Min to Max
V
Note 1: For operation in ambient temperature above 25 C, the device must be derated based on a 150 C maximum junction temperature and a thermal resistance
§
§
junction to ambient, as follows: LM832N 90 c/w, LM832M-115 c/w.
b
§
§
Note 2: To force the DNR system into maximum bandwidth, connect a 2k resistor from pin 9 to GND. AC ground pin 9 or pin 6 to select minimum bandwidth. To
change minimum and maximum bandwidth, see Application Hints.
Note 3: The maximum noise reduction CCIR/ARM weighted is about 14 dB. This is accomplished by changing the bandwidth from maximum to minimum. In actual
operation, minimum bandwidth is not selected, a nominal minimum bandwidth of about 2 kHz gives 10 dB of noise reduction. See Application Hints.
2
External Component Guide (SeeFigure 1)
Recom-
Effect
P/N
mended
Value
Purpose
Remarks
Smaller
Poor supply
Larger
C1
10 mF
1 mF
Power supply
Better supply
rejection
Do not use less
decoupling
rejection
than 10 mF
C2,C11
Input coupling
capacitor
Increases
Reduces
DC voltage at pin 2
and pin 13 is 0.35V
frequency of low-
frequency roll-off
frequency of low-
frequency roll-off
1
e
f
2qC R
2
IN
C3,C10 22 nF for Stereo, Establishment of Min
Bandwidth
Bandwidth
See Note 4
15 nF for mono
and Max Bandwidth
becomes wider
becomes narrower
C4,C8
1 mF
Output coupling
capacitor
Increases
Reduces
DC voltage at pin 4
and pin 11 is 0.35V
frequency of low-
frequency roll-off
frequency of low-
frequency roll-off
1
e
f
2qC R
4
LOAD
Works with R1 and R2 Some high frequency Bandwidth may
to set one of the low-
frequency corners
in control path
program material
may be attenuated
increase due
to low-frequency
inputs, causing
‘‘Breathing’’
1
e
e
1.6 kHz
C5
C6
0.1 mF
f
a
2qC (R1 R2)
5
See Note 4
Works with input
resistance of pin 6
to set one of the
low-frequency
corners in the
1
e
e
e
820 pF
Same as
above
Same as
above
f
4.8 kHz
2qC R
6
PIN6
See Note 4
control path
Works with input
resistance of pin 9
to form part of
Same as
above
Same as
above
1
2qC R
e
C7
C9
39 nF
f
4.8 kHz
7
PIN7
control path
frequency weighing
See Note 4
See Note 4
1 mF
Sets attack time
Reduces attack
and decay time
Increases attack
and decay time
This voltage
divider sets
control path
sensitivity
Sensitivity should be set for
maximum noise reduction
and minimum audible
frequency program effect
on high
a
e
1 kX
R1,R2
R
1
R
Ð
Ð
2
R3
2 kX
Sets gain amp load
when DNR is OFF
Loads gain amp
output, may
Max bandwidth
will be reduced
#
cause distortion
Note 4: The values of the control path filter components (C5, C6, C7, C9, R1, R2) and the integrating capacitors (C3, C10) should not be changed from the
recommended values unless the characteristics of the noise or program material differ substantially from that of FM or tape sources. Failure to use the correct
values may result in degraded performance, and therefore the application may not be approved for DNR trademark usage. Please contact National Semiconductor
for more information and technical assistance.
3
Typical Performance Characteristics
TL/H/5176–4
TL/H/5176–2
TL/H/5176–3
FIGURE 4. Power supply
rejection ratio vs frequency
FIGURE 2. Supply current
vs supply voltage
FIGURE 3. Channel separation
vs frequency
TL/H/5176–5
TL/H/5176–7
FIGURE 7. THD vs
frequency
TL/H/5176–6
FIGURE 6. Output level
vs frequency
FIGURE 5. Output level
change vs supply voltage
TL/H/5176–9
FIGURE 9. Frequency response
for various input levels
TL/H/5176–8
TL/H/5176–10
FIGURE 10. Gain of control
path vs frequency
FIGURE 8. Output vs frequency
and control path signal
TL/H/5176–11
FIGURE 11. Change in main signal path
maximum bandwidth vs temperature
4
Circuit Operation
The LM832 has two signal paths, a main signal path and a
bandwidth control path. The main path is an audio low pass
filter comprised of a g block with a variable current, and a
m
unity gain buffer. As seen in Figure 1, DC feedback con-
acts as an integrator and is unable to detect it. Because of
this, signals of sufficient energy to mask noise open the
bandwidth to 90% of the maximum value in less than 1 ms.
Reducing the bandwidth to within 10% of its minimum value
is done in about 60 ms: long enough to allow the ambience
of the music to pass through, but not so long as to allow the
noise floor to become audible.
e b
frequency of the filter, the output decreases at 6 dB/oct
strains the low frequency gain to A
1. Above the cutoff
b
v
due to the action of the 0.022 mF capacitor.
The purpose of the control path is to generate a bandwidth
control signal which replicates the ear’s sensitivity to noise
in the presence of a tone. A single control path is used for
both channels to keep the stereo image from wandering.
This is done by adding the right and left channels together
in the summing amplifier of Figure 1. The R1, R2 resistor
divider adjusts the incoming noise level to slightly open the
bandwidth of the low pass filter. Control path gain is about
60dB and is set by the gain amplifier and peak detector
gain. This large gain is needed to ensure the low pass filter
bandwidth can be opened by very low noise floors. The ca-
pacitors between the summing amplifier output and the
peak detector input determine the frequency weighting as
shown in the typical performance curves. The 1 mF capaci-
tor at pin 10, in conjunction with internal resistors, sets the
attack and decay times. The voltage is converted into a
3. Reducing the audio bandwidth reduces the audibility of
noise. Audibility of noise is dependent on noise spectrum, or
how the noise energy is distributed with frequency. Depend-
ing on the tape and the recorder equalization, tape noise
spectrum may be slightly rolled off with frequency on a per
octave basis. The ear sensitivity on the other hand greatly
increases between 2 kHz and 10 kHz. Noise in this region is
extremely audible. The DNR system low pass filters this
noise. Low frequency music will not appreciably open the
DNR bandwidth, thus 2 kHz to 20 kHz noise is not heard.
Application Hints
The DNR system should always be placed before tone and
volume controls as shown in Figure 1. This is because any
adjustment of these controls would alter the noise floor
seen by the DNR control path. The sensitivity resistors R1
and R2 may need to be switched with the input selector,
depending on the noise floors of different sources, i.e., tape,
FM, phono. To determine the value of R1 and R2 in a tape
system for instance; apply tape noise (no program material)
and adjust the ratio of R1 and R2 to slightly open the band-
width of the main signal path. This can easily be done by
viewing the capacitor voltage of pin 10 with an oscilloscope,
or by using the circuit of Figure 12. This circuit gives an LED
display of the voltage on the peak detector capacitor. Adjust
the values of R1 and R2 (their sum is always 1 kX) to light
the LEDs of pin 1 and pin 18. The LED bar graph does not
indicate signal level, but rather instantaneous bandwidth of
the two filters; it should not be used as a signal-level indica-
tor. For greater flexibility in setting the bandwidth sensitivity,
R1 and R2 could be replaced by a 1 kX potentiometer.
proportional current which is fed into the g blocks. The
m
bandwidth sensitivity to g current is 70 Hz/mA. In FM
m
stereo applications a 19 kHz pilot filter is inserted between
pin 8 and pin 9 as shown in Figure 16.
Normal methods of evaluating the frequency response of
the LM 832 can be misleading if the input signal is also
applied to the control path. Since the control path includes a
frequency weighting network, a constant amplitude but vary-
ing frequency input signal will change the audio signal path
bandwidth in a non-linear fashion. Measurements of the au-
dio signal path frequency response will therefore be in error
since the bandwidth will be changing during the measure-
ment. See Figure 9 for an example of the misleading results
that can be obtained from this measurement approach. Al-
though the frequency response is always flat below a single
high-frequency pole, the lower curves do not resemble sin-
gle pole responses at all.
To change the minimum and maximum value of bandwidth,
the integrating capacitors, C3 and C10, can be scaled up or
down. Since the bandwidth is inversely proportional to the
capacitance, changing this 0.022 mF capacitor to 0.015 mF
will change the typical bandwidth from 1 kHz–30 kHz to 1.5
kHz–44 kHz. With C3 and C10 set at 0.022 mF, the maxi-
mum bandwidth is typically 30 kHz. A double pole double
throw switch can be used to completely bypass DNR.
A more accurate evaluation of the frequency response can
be seen in Figure 8. In this case the main signal path is
frequency swept while, the control path has a constant fre-
quency applied. It can be seen that different control path
frequencies each give a distinctive gain roll-off.
PSYCHOACOUSTIC BASICS
The capacitor on pin 10 in conjunction with internal resistors
sets the attack and decay times. The attack time can be
altered by changing the size of C9. Decay times can be
decreased by paralleling a resistor with C9, and increased
by increasing the value of C9.
The dynamic noise reduction system is a low pass filter that
has a variable bandwidth of 1 kHz to 30 kHz, dependent on
music spectrum. The DNR system operates on three princi-
ples of psychoacoustics.
1. Music and speech can mask noise. In the absence of
source material, background noise can be very audible.
However, when music or speech is present, the human ear
is less able to distinguish the noiseÐthe source material is
said to mask the noise. The degree of masking is depen-
dent on the amplitude and spectral content (frequencies) of
the source material, but in general multiple tones around 1
kHz are capable of providing excellent masking of noise
over a very wide frequency range.
When measuring the amount of noise reduction of DNR in a
cassette tape system, the frequency response of the cas-
sette should be flat to 10 kHz. The CCIR weighting network
has substantial gain to 8 kHz and any additional roll-off in
the cassette player will reduce the benefits of DNR noise
reduction. A typical signal-to-noise measurement circuit is
shown in Figure 13. The DNR system should be switched
from maximum bandwidth to nominal bandwidth with tape
noise as a signal source. The reduction in measured noise is
the signal-to-noise ratio improvement.
2. The ear cannot detect distortion for less than 1 ms. On a
transient basis, if distortion occurs in less than 1 ms, the ear
5
Application Hints (Continued)
TL/H/5176–12
FIGURE 12. Bar Graph Display of Peak Detector Voltage
TL/H/5176–13
FIGURE 13. Technique for Measuring S/N Improvement of the DNR System
CASCADE CONNECTION
Additional noise reduction can be obtained by cascading the
DNR filters. With two filters cascaded the rolloff is 12 dB per
octave. For proper operating bandwidth the capacitors on
pin 3 and 12 are changed to 15 nF. The resulting noise
reduction is about 17 dB.
Figure 15 shows the monaural cascade connection. Note
that pin 14 is grounded so only the pin 2 input is fed to the
summing amp and therefore the control path.
Figure 14 shows the stereo cascade connection. Note that
pin 14 is open circuit as in normal stereo operation.
TL/H/5176–14
a
e
1 kX (refer to application hints)
*R1
R2
FIGURE 14. Stereo Cascade Connection
6
Application Hints (Continued)
TL/H/5176–15
a
e
1 kX (refer to application hints)
*R1
R2
FIGURE 15. Monaural Cascade Connection
FM STEREO
When using the DNR system with FM stereo as the audio
source, it is important to eliminate the ultrasonic frequencies
that accompany the audio. If the radio has a multiplex filter
to remove the ultrasonics there will be no problem.
Standard audio multiplex filters are available for use at the
output of the demodulator from several filter companies.
Figure 16 shows the additional components L1, C15 and
C16 that are added to the control path for FM stereo appli-
cations. The coil must be tuned to 19 kHz, the FM pilot
frequency.
This filtering can be done at the output of the demodulator,
before the DNR system, or in the DNR system control path.
a
e
*R1 R2 1 KX
(refer to application hints)
TL/H/5176–16
FIGURE 16. FM Stereo Application
FOR FURTHER READING
Tape Noise Levels
Noise Masking
1. ‘‘Masking and Discrimination’’, Bos and De Boer, JAES,
Ý
Volume 39, 4, 1966.
1. ‘‘A Wide Range Dynamic Noise Reduction System’’
Blackmer, ‘dB’ Magazine, August-September 1972, Volume
Ý
6, 8.
2. ‘‘The Masking of Pure Tones and Speech by White
Ý
Noise’’, Hawkins and Stevens, JAES, Volume 22, 1, 1950.
2. ‘‘Dolby B-Type Noise Reduction System’’, Berkowitz and
Gundry, Sert Journal, May-June 1974, Volume 8.
3. ‘‘Sound System Engineering’’, Davis, Howard W. Sams
and Co.
3. ‘‘Cassette vs Elcaset vs Open Reel’’, Toole, Audioscene
Canada, April 1978.
4. ‘‘High Quality Sound Reproduction’’, Moir, Chapman Hall,
1960.
4. ‘‘CCIR/ARM: A Practical Noise Measurement Method’’,
Dolby, Robinson, Gundry, JAES, 1978.
5. ‘‘Speech and Hearing in Communication’’, Fletcher, Van
Nostrand, 1953.
7
LM832 Simple Circuit Schematic
8
9
Physical Dimensions inches (millimeters)
Order LM832M
NS Package Number M14A
Order LM832N
NS Package Number N14A
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL
SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and whose
failure to perform, when properly used in accordance
with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury
to the user.
2. A critical component is any component of a life
support device or system whose failure to perform can
be reasonably expected to cause the failure of the life
support device or system, or to affect its safety or
effectiveness.
National Semiconductor
Corporation
National Semiconductor
Europe
National Semiconductor
Hong Kong Ltd.
National Semiconductor
Japan Ltd.
a
1111 West Bardin Road
Arlington, TX 76017
Tel: 1(800) 272-9959
Fax: 1(800) 737-7018
Fax:
(
49) 0-180-530 85 86
@
13th Floor, Straight Block,
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Tel: (852) 2737-1600
Fax: (852) 2736-9960
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Email: cnjwge tevm2.nsc.com
a
a
a
a
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(
(
(
(
49) 0-180-530 85 85
49) 0-180-532 78 32
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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
This datasheet has been download from:
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