3845
AM NOISE BLANKER
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’).
Data Sheet
27126B*
RF IN
RF BYPASS
RF BIAS
RF AGC
AUDIO DELAY
AUDIO BLANK
TIME (R)
NO
CONNECT
AUDIO BLANK
TIME (C)
AUDIO OUT
1
AUDIO IN
1
1
2
3
4
5
6
7
8
9
10
NC
DET
V
CC
NC
20
19
18
17
16
15
SUPPLY
NO
CONNECT
RF GATE
LOW
RF GATE
HIGH
GROUND
RF BLANK
TIME
NO
CONNECT
NOISE
DIFFERENTIATOR
AUDIO OUT
2
AUDIO IN
2
NC
14
13
12
11
Dwg. PS-003-1A
FEATURES
I
I
I
I
I
I
I
RF Blanking to 30 MHz
Single-Channel or Stereo Audio Blanking
Adjustable RF and Audio Blanking Time
Adjustable Audio Blanking Delay
Sample-and-Hold MOS Audio Gates
Internal Voltage Regulation
Minimum External Components
AM and AM-Stereo Automotive Radios
CB Transmitter/Receivers
Short-Wave Receivers
Mobile Communications Equipment
ABSOLUTE MAXIMUM RATINGS
at T
A
= +25
°
C
Supply Voltage, V
CC
. . . . . . . . . . . . . .
Package Power Dissipation,
P
D
. . . . . . . . . . . . . . . . . . . . . . .
12 V
APPLICATIONS
I
I
I
I
1.78 W
Operating Temperature Range, T
A
Suffix ‘ELW’ . . . . . . . .
-40
°
C to +85
°
C
Suffix ‘SLW’ . . . . . . . .
-20
°
C to +85
°
C
Storage Temperature Range,
T
S
. . . . . . . . . . . . . . . .
-55
°
C to +125
°
C
Always order by complete part number:
Part Number
A3845ELW
A3845SLW
Function
Stereo Noise Blanker, Extended Temp. Range
Stereo Noise Blanker, Standard Temp. Range
ALLEGRO [ ALLEGRO MICROSYSTEMS ]
