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PT4316 V1.6

- 8 -

August, 2007

Low Power 315/433 MHz OOK/ASK Superheterodyne

Receiver with SAW-based Oscillator

PT4316

For down-converting the RF signal to the IF frequency, a suitable SAW oscillation frequency must be

chosen. For the PT4316, the -3dB bandwidth of the IF chain is located from 250KHz to 3.1MHz and its

optimum value is around 1.2MHz. The following equation may be utilized to calculate an appropriate

SAW oscillator frequency.

SAW Oscillator (Freq.) = TX (Freq.) +/

– (250KHz ~ 3.1MHz)

In addition to a SAW resonator, the resonant circuit may also be achieved by an “L-C tank”. The

recommended circuit for an “L-C tank” is as the following figure.

16

OSCIN

OSCOUT

15

C14

C15

LIMITER/RSSI

The limiter is an AC coupled multi-stage amplifier with a cumulative gain of approximately 70dB that

5MHz (from 250KHz to 5.2MHz). The limiter circuit also produces an RSSI voltage that is directly

proportional to the input signal level with a slope of approximately 14mV/dB. This signal is used to

demodulate ASK-modulated receive signals in the subsequent baseband circuitry.

Frequency

(MHz)

C14

(pF)

C15

(pF)

Trimmer L3

(H)

315

100

10

2.5 T

433.92

100

5.6

1.5 T