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PT4316 V1.6

- 5 -

August, 2007

Low Power 315/433 MHz OOK/ASK Superheterodyne

Receiver with SAW-based Oscillator

PT4316

FUNCTION DESCRIPTION

The PT4316 CMOS superheterodyne receiver provides the functionality of a complete receive chain

from an antenna input to digital data output. Depending upon signal power and component selection,

data rates as high as 50 Kb/s may be achieved.

LOW NOISE AMPLIFIER (LNA)

The LNA is an on-chip cascode amplifier with a power gain of 16dB and a noise figure of 3dB. The gain

is determined by external matching networks situated ahead of the LNA and between the LNA output

and the mixer input.

An example of the input matching network and the input impedance of PT4316 for 315/434MHz bands

are shown in the following figure. The component values given in the table following the application

circuit are nominal values only. For a particular PCB layout, the user may be required to make

component adjustments in order to achieve highest sensitivity.

C3

C4

C2

3

RFIN

Frequency

(MHz)

LNA Input Impedance (Pin 3)

Normalized to 50

Ω

315

4.18

—j251.63

433.92

3.60

—j180.20

The LNA output of PT4316 internally connects to the mixer stage so that its output impedance cannot

be measured directly. The LNA output requires a DC supply through a choke inductor. For obtaining

better LNA gain, a capacitor is recommended to be added in parallel with this inductor to implement a

resonant tank at the desired frequency as shown in the following figure. Note that the LNA might

self-oscillate and degrade the receiver sensitivity, particularly if a large inductor value is chosen. An

alternate matching method is to replace the parallel capacitor with a 330 to 1K

Ω resistor, which would

reduce the resonant tank Q (quality factor) and avoid the self-oscillation.

C5

C8

5

LNAOUT

R1

L2

VDD