A3845 ALLEGRO [Allegro MicroSystems], A3845 Datasheet - Page 5

• Manufacturer Part Number: A3845
• Description: AM NOISE BLANKER
• Manufacturer: ALLEGRO [Allegro MicroSystems]

under one or more U.S. patents or U.S. patents
pending.
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.
critical components in life-support devices or systems
without express written approval.
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.
BW = "WIDE"
ANTENNA
The products described here are manufactured
Allegro MicroSystems, Inc. reserves the right to
Allegro products are not authorized for use as
The information included herein is believed to be
www.allegromicro.com
PULSE
NOISE
0.5 µs
20 kHz
50 µs
RF
MIXER
500 µs
where R
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.
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.
Blanking in the RF or mixer sections of the receiver removes most of the
15
12 kHz
should be greater than 33 kΩ. Smaller values for C
IF
600 µs
IF LIMITING
AM NOISE BLANKER
AUDIO
5 kHz
13
will reduce
3845
Dwg. OS-001A