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URL: http://www.princeton.com.tw
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.
OSCOUT
16
C14
OSCIN
15
C15
Frequency
(MHz)
315
433.92
C14
(pF)
100
100
C15
(pF)
10
5.6
Trimmer L3
(H)
2.5 T
1.5 T
LIMITER/RSSI
The limiter is an AC coupled multi-stage amplifier with a cumulative gain of approximately 70dB that
has a band-pass characteristic centered around 2MHz. The
-
3dB bandwidth of the limiter is around
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.
PT4316 V1.6
-8-
August, 2007
PTC [ PRINCETON TECHNOLOGY CORP ]
