KESRX05

260 to 470MHz ASK Receiver with Power Down

Preliminary Information

DS5023 Issue 1.9 August 1999

REF

ANTI

JAM

DATA

FILTER

RSSI DETECTOR

NOISE

REDUCTION

FILTER

CERAMIC

IF FILTER

SLICER

PHASE LOCKED LOOP

AGC

LNA

MIXER

LOOP

FILTER

SAW

FILTER

VCO

RF INPUT

XTAL

PHASE

DETECTOR

SLICED

DATA

20·5V to 17V

255

°C to 150°C

255

°C to 150°C

120dBm from 50

Features

In-band Interference Rejection 20dB max.

2103dBm Sensitivity (IF BW = 470kHz)

AGC around LNA and Mixer

Low Supply voltage (3 to 6V)

2-Stage Power Down for Low Current Applications

Interface for Ceramic IF Filters up to 15MHz

All Pins Meet 2kV Human Body Model ESD
Protection Requirement

Compliant to ETS 300-220 and FCC Part 15

Applications

Remote Keyless Entry

Security, tagging

Remote Controlled equipment

Absolute Maximum Ratings

Supply voltage, V

Storage temperature,T

stg

Junction temperature, T

RF input power

Ordering Information

KESRX05B/KG/QP1S (anti-static tubes)
KESRX05B/KG/QP1T (tape and reel)

The KESRX05 is a single chip ASK (Amplitude Shift Key)
Receiver IC. It is designed to operate in a variety of low
power radio applications including keyless entry, general
domestic and industrial remote control, RF tagging and
local paging systems.

The receiver offers an exceptionally high level of integration
and performance to meet the local oscillator radiation
requirements of regulatory authorities world wide.
Functionally the device works in the same way as the
KESRX01 with the added features of low supply voltage,
in-band interference rejection (anti-jamming detector), a
2-stage power down to enable receiver systems to be
implemented with less than 1mA supply, and a wide IF
bandwidth and drive stage to interface to an external
ceramic IF bandpass filter at intermediate
frequencies from 0·2MHz to 15MHz.

The KESRX05 is an ideal receiver for difficult reception
areas where high level interferers would jam the wanted
signal. The anti-jamming circuit allows operation to be
possible with interfering signals which are more than 20dB
stronger than the wanted signal, without the cost penalties
of increased IF selectivity and frequency accuracy.

Figure 1 Typical system application

KESRX05

Figure 2 Pin connections (top view)

the performance for a wide range of applications and
locations world wide.

he KESRX05, with its anti-jamming detector circuit, is

an ideal ASK/ OOK receiver for difficult reception areas
caused by interference such as amateur radio repeater
stations and wireless stereo headphones. Operation is
possible with interfering signals which are more than
20dB stronger than the wanted signal (IF bandwidth =
470kHz.), without the cost penalities of increased IF se-
lectivity and frequency accuracy.

Figure 1 is the system block diagram, with an external
ceramic IF filter, SAW fillter and noise reduction filter.

IFFLT1

IFDC1

IFIN

IFDC2

IFOUT

MIXIP

RFOP

RFIN

AGC

PEAK

DATAOP

IFFLT2

RSSI

DETB

XTAL1

XTAL2

DF0

DF1

DF2

VCO1

VCO2

DSN

KESRX05

DESCRIPTION

The single conversion superheterodyne receiver
approach is now generally considered the way forward
for ISM band type applications because of lower cost,
superior selectivity, lower radiation, and flexibility over
other techniques. For power-conscious, hand-held
applications KESRX05 provides improved performance
and flexibility on a lower 3·0V supply and a power down
feature allows faster switch-on times for use in a pulsed
power saving mode.

Although this is a relatively simple receiver, the flexibility
of using an external IF filter allows the designer to
choose both the selectivity and the IF in order to optimise

Pin

Name

Function

Schematic

IFFLT1

Table 1 Pin descriptions

Cont...

IFFLT1

IFFLT2

10k

Noise reducing IF filter

A simple LC noise reduction filter (L5 and C7) is
connected between pins 1 (IFFLT1 ) and 28 (IFFLT2)
to reduce the noise contribution from the earlier
stages of the logathrimic amplifier. The LC filter helps
to reduce the bandwidth of the log amplifier from
approximately 45MHz to typically 1MHz, preventing
wideband noise from being detected as a signal. To
reduce the Q of the simple LC circuit, an external
damping resistor in parallel with L5, C7. However,
the preferred method to a damping resistor is to lower
the Q of L5 or increase the tolerances of L5 and C7.

For further information refer to the
IF Amp /RSSI Detector section of the Functional Description.

KESRX05

Pin

Name

Function

Schematic

IFDC1

IFIN

IFDC2

IFOUT

MIXIP

Log Amplifier DC Blocking Capacitor

Capacitors C3 and C4 provide DC blocking within
the high gain stage of the log amplifier. The log
amplifier has a small gain of greater than 80dB
between pins 3 (IFIN) and 27 (RSSI output)
Capacitors C3 and C4 eliminate DC offsets, allowing
the amplification of AC signals only.

For further information, refer to the IF Amp/RSSI De-
tector section of the Functional Description.

Log Amp Input (IFamplifier input)

The bandwidth of KESRX05 is set by the external
ceramic filter CF1. Impedance matching from the
output of the ceramic filter to the input of the log
amplifier is achieved by an external shunt resistor
R9 in parallel with an internal resistor.

For further information please refer to the IF Interface
section of the Functional Description.

Log amplifier DC stability capacitor

Positive supply

IF output

The IF output drive is a voltage drive with a low output
impedance of 300

via an internal series resistor.

The IFOUT pin is designed for direct connection to
an external 10·7MHz FM ceramic filter with a typical
input impedance of 300

For further information refer to the IF Interface section
of the Functional Description.

Positive supply for RF circuits

Mixer input

To a first order approximation the input impedance
of the mixer at UHF frequencies is set by the internal
bias resistor and capacitor network. Effects of internal
and external stray parasitics ignored.

For further information refer to the AC Electrical
Characteristics.

IFIN

3·1k

950

181k

IFDC

IFDC1

IFIN

3·1k

181k

INTERNAL

FROM

CF1

Matching circuit for CF1

See pin 2

Table 1 Pin descriptions (continued)

Cont...

IFOUT

300

µA

MIXIP

KESRX05

Pin

Name

Function

Schematic

RFOUT

RFIN

AGC

PEAK

DATAOP

Output from internal RF amplifier

The RF amplifier has a high output impedance. The
internal 300

resistor is used to improve the ESD

protection of RFOUT.

For further information refer to the AC Electrical
Characteristics.

Negative supply for RF circuits

nternal input RF amplifier

To a first order approximation the input impedance
of the RF amplifier at UHF frequencies is set by the
internal bias resistor and capacitor network. Effects
of internal and external stray parasitics ignored.

For further information please refer to the AC
Electrical Characteristics.

RF AGC time constant

The attack and decay time constant of the AGC is
set by the internal series resistor, current sink and
the external capacitor C8. Increasing the decay time
constant of the AGC circuit will impair the time to
good data of the receiver from power up PD0 to PD2.

For further information please refer to the IF Amp/
RSSI Detector section of the Functional Description.

Data signal peak detector output

The peak detector output is designed to be a low
impedance output. The peak detector monitors the
peak of the signal at pin 20 (DF2).

For further information please refer to the Baseband
section of the Functional Description.

Sliced data output

The data output is the inverted sense of the input
signal at pin 20 (DF2) and is designed as a high im-
pedance output via two internal sink and source cur-
rent generators

RFOP

300

240

µA

(AGC OFF)

830

10p

RFIN

240

µA

360

AGC

µA

190k

300

PEAK

DATAOP

µA

HIGH

LOW

Table 1 Pin descriptions (continued)

Cont...

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