A3845ELW Datasheet PDF - Allegro MicroSystems
| Part Number | A3845ELW | |
| Description | AM NOISE BLANKER | |
| Manufacturers | Allegro MicroSystems | |
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3845
AM NOISE BLANKER
RF IN 1
RF BYPASS 2
RF BIAS 3
RF AGC 4
AUDIO DELAY 5
AUDIO BLANK
TIME (R)
NO
CONNECT
AUDIO BLANK
TIME (C)
6
7
8
AUDIO OUT1 9
NC
AUDIO IN1 10
DET
VCC 20 SUPPLY
NC
19
NO
CONNECT
RF GATE
18 LOW
17 RF GATE
HIGH
16 GROUND
15 RF BLANK
TIME
NC 14 NO
CONNECT
13 NOISE
DIFFERENTIATOR
12 AUDIO OUT2
11 AUDIO IN 2
Dwg. PS-003-1A
This noise blanker integrated circuit contains all of the necessary
circuitry for adding an extremely efficient (patented) noise-blanking
technique to any type of AM tuner or receiver with RF input frequen-
cies (or a first IF) to 30 MHz. The A3845ELW and A3845SLW
feature dual audio channels and are intended for AM-stereo or indepen-
dent sideband applications.
A high input impedance, high-gain, broadband RF amplifier
permits these devices to be directly connected to the RF stage of a
tuner. Internal AGC circuitry ensures that the noise detection threshold
remains constant with changes in input signal level. The RF gate
response time is sufficiently fast to blank the noise pulse at the output
of the mixer before the IF filter. Short blanking times effectively
suppress most of the interfering noise. Residual audio noise is re-
moved by an audio sample-and-hold gate. The RF blanking time,
audio gate delay time, and audio gate blanking time can all be indepen-
dently adjusted to suit the particular application.
These AM noise blankers are packaged in plastic SOICs and are
rated for operation over the a standard temperature range of -20°C to
+85°C (suffix ‘SLW’) or an extended temperature range to -40°C
(suffix ‘ELW’).
ABSOLUTE MAXIMUM RATINGS
at TA = +25°C
Supply Voltage, VCC . . . . . . . . . . . . . . 12 V
Package Power Dissipation,
PD . . . . . . . . . . . . . . . . . . . . . . . 1.78 W
Operating Temperature Range, TA
Suffix ‘ELW’ . . . . . . . . -40°C to +85°C
Suffix ‘SLW’ . . . . . . . . -20°C to +85°C
Storage Temperature Range,
TS . . . . . . . . . . . . . . . . -55°C to +125°C
FEATURES
I RF Blanking to 30 MHz
I Single-Channel or Stereo Audio Blanking
I Adjustable RF and Audio Blanking Time
I Adjustable Audio Blanking Delay
I Sample-and-Hold MOS Audio Gates
I Internal Voltage Regulation
I Minimum External Components
APPLICATIONS
I AM and AM-Stereo Automotive Radios
I CB Transmitter/Receivers
I Short-Wave Receivers
I Mobile Communications Equipment
Always order by complete part number:
Part Number Function
A3845ELW
A3845SLW
Stereo Noise Blanker, Extended Temp. Range
Stereo Noise Blanker, Standard Temp. Range
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3845
AM NOISE BLANKER
TYPICAL PULSE RESPONSE
ANTENNA
BW = "WIDE"
RF
20 kHz
MIXER
IF
12 kHz
AUDIO
5 kHz
0.5 µs
NOISE
PULSE
50 µs
500 µs
IF LIMITING
600 µs
Dwg. OS-001A
The products described here are manufactured
under one or more U.S. patents or U.S. patents
pending.
Allegro MicroSystems, Inc. reserves the right to
make, from time to time, such departures from the
detail specifications as may be required to permit
improvements in the performance, reliability, or
manufacturability of its products. Before placing an
order, the user is cautioned to verify that the informa-
tion being relied upon is current.
Allegro products are not authorized for use as
critical components in life-support devices or systems
without express written approval.
The information included herein is believed to be
accurate and reliable. However, Allegro
MicroSystems, Inc. assumes no responsibility for its
use; nor for any infringement of patents or other rights
of third parties which may result from its use.
where R15 should be greater than 33 kΩ. Smaller values for C13 will reduce
the sensitivity to RF input pulses. The MOSFET turns ON within approxi-
mately 1.5 µs (shunting the RF signal to ground) after a noise pulse is
detected and then turns OFF over a 15 µs period after the end of the RF gate
time. The ON resistance of the MOSFET is about 30 Ω. The slow turn-OFF
prevents any additional transients from being introduced into the receiver by
the RF gate. The internal gate circuit also includes charge-balancing circuits
so that switching transients are canceled and do not appear at the output.
These features ensure transient-free switching even when the RF gate is
connected to the low-level input stages of a receiver. Note that the RF gate
must be connected to a supply to obtain the minimum ON-resistance of the
MOSFET gate. This makes it convenient to connect the RF gate in parallel
with the receiver mixer output transformer primary.
Blanking in the RF or mixer sections of the receiver removes most of the
noise pulse but a small amount still remains due to the hole punched in the
carrier. This residual noise is theoretically somewhere between the peak
audio and 100% negative modulation but is significantly smaller and narrower
than that which the impulse would normally produce without blanking. An
audio delay, one-shot, and audio gates are included to eliminate this residual
signal.
www.allegromicro.com
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| Information | Total 8 Pages | |
| Link URL | [ Copy URL to Clipboard ] | |
| Download | [ A3845ELW.PDF Datasheet ] | |
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