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TR8100-021307

ASH Receiver Block Diagram & Timing Cycle

Antenna

Pulse

Generator

SAW

Delay Line

SAW Filter

RFA1

RFA2

Data

Out

Detector &

Low-Pass

Filter

RF Data Pulse

P1

P2

RFA1 Out

RF Input

P1

Delay Line

Out

P2

t

PW2

t

PW1

t

PRI

t

PRC

Figure 1

ASH Transceiver Theory of Operation

Introduction

RFM’s amplifier-sequenced hybrid (ASH) transceiver technology is specif-

ically designed for short-range wireless data communication applications.

ASH transceivers provide robust operation, very small size, low power

consumption and low implementation cost. All critical RF functions are

contained in the hybrid, simplifying and speed-ing design-in. ASH trans-

ceivers can be readily configured to support a wide range of data rates

and protocol requirements. These transceivers feature excellent suppres-

sion of transmitter harmonics and virtually no RF emissions when receiv-

ing, making them easy to certify to short-range (unlicensed) radio

regulations.

Amplifier-Sequenced Receiver Operation

The ASH transceiver’s unique feature set is made possible by its system

architecture. The heart of the transceiver is the amplifier-sequenced

receiver section, which provides more than 100 dB of stable RF and

detector gain without any special shielding or decoupling requirements.

Figure 1 shows the basic block diagram and timing cycle for an amplifier

sequenced receiver. Note that the bias to RF amplifiers RFA1 and RFA2

are independently controlled by a pulse generator, and that the two ampli-

fiers are coupled by a surface acoustic wave (SAW) delay line, which has

a typical delay of 0.5 µs.

An incoming RF signal is first filtered by a narrow-band SAW filter, and is

then applied to RFA1. The pulse generator turns RFA1 ON for 0.814 µs.

The amplified signal from RFA1 emerges from the SAW delay line at the

input to RFA2. RFA1 is now switched OFF and RFA2 is switched ON for

0.814 µs, amplifying the RF signal further. The ON time for RFA1 and

RFA2 is set by a 614 kHz internal pulse generator. As shown in the timing

diagram, RFA1 and RFA2 are never on at the same time, assuring excel-

lent receiver stability. Note that the narrow-band SAW filter eliminates

sampling sideband responses outside of the receiver passband, and the

SAW filter and delay line act together to provide very high receiver ulti-

mate rejection.

ASH Transceiver Block Diagram

Figure 2 is the general block diagram of the ASH transceiver.

Please refer to Figure 2 for the following discussions.

Antenna Port

The only external RF components needed for the transceiver are the

antenna and its matching components. Antennas presenting an imped-

ance in the range of 35 to 72 ohms resistive can be satisfactorily matched

to the RFIO pin with a series matching coil and a shunt matching/ESD pro-

tection coil. Other antenna impedances can be matched using two or

three components. For some impedances, two inductors and a capacitor

will be required. A DC path from RFIO to ground is required for ESD pro-

tection.