TELEFUNKEN Semiconductors
U4314B
Logarithmic AM Demodulator / RSSI
Description
The U4314B is a monolithic Integrated Circuit in bipolar
technology for low current super-heterodyne receivers. It
can be used as a logarithmic
Received Signal Strength
Indicator
(RSSI) or as a logarithmic AM demodulator. Its
bandwidth is optimized for intermediate frequencies of
9 to 10.7 MHz (see figure 9).
Its low current consumption and wide power supply volt-
age range make this IC predestined to add a temperature
compensated field strength indication to new or existing
receiver or instrumentation designs, missing such a func-
tion.
It can also be used as a logarithmic AM demodulator. Its
dynamic range in excess of 60 dB (see figure 10) supports
a receiver design without the need of an automatic gain
control (AGC). The usable data rate is up to several
hundred kBauds. Typical applications are keyless entry
and alarm systems for cars and buildings.
The U4314B supports a superhet receiver design with less
than 1 mA total current consumption, which is a peremp-
tory requirement claimed by international car
manufacturers. As this IC needs only 3.0 V supply volt-
age, the front end may be a stacked design in order to
reach this extremely low total receiver current consump-
tion.
A proposal for a discrete RF front end with a surface
acoustic wave (SAW) resonator based local oscillator
special low current UHF-transistors like S822T or S852T
can be found in the application notes ANT012 and
ANT013.
Features
D
Logarithmic RSSI / AM demodulator output
D
Sensitive IF-amplifier for 10.7 MHz operating
frequency
D
Wide power supply voltage range 3 to 12 V
D
Temperature compensated reference voltage of 2.4 V
externally available
D
Usable for ASK data systems up to several hundred
kBauds
D
Only one additional part (capacitor) necessary
D
ESD hardened
D
Extreme low current consumption typically 0.8 mA
Block diagram
V
S
8
5
IF
in
IF 鈥?amplifier
V
Ref
internal
Log RSSI /
AM demodulator
1, 2, 3, 6
95 10215
8
Bandgap
V
Ref
C
Ref
4
log RSSI
log AM
out
GND
Figure 1. Block diagram
Rev. A1: 26.06.1995
1 (7)
1
2
3
4
5
6
7
