WIDEBAND FM/FSK IF RECEIVER

S1T8531

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FUNCTIONAL DESCRIPTION

General

The S1T8531 is a wideband FM / FSK receiver designed for use in analog FM and digital FSK systems such as

900MHz / 2.4GHz ISM band analog / digital cordless phones and wideband data links with data rates up to 2Mbps.

It contains IF amplifier, quadrature detector, baseband filter amplifier and data slicer with sample and hold function.

IF Amplifier

The IF amplifier section is composed of seven differential stage with total gain of 100dB at 10.7MHz. The input

impedance at 10.7MHz is 1.5k

Ω. For 10.7MHz ceramic filter applications, an external 430Ω resistor must be placed

between IFP(Pin15) and IFN(pin16) to provide the equivalent load impedance of 330

Ω that is required by the filter.

Quadrature Demodulator

The quadrature demodulator requires tank circuit with loaded Q depending on detection bandwidth. Following

figure shows external components required for 10.7MHz operation.

Baseband Filter Buffer Amplifier3

Baseband filter amplifier is a wideband buffer and it can be configured as a second-order sallen-key low pass filter.

Following figure shows the external components required.

Cutoff frequency = 1 / [2

π*SQRT(R1R2C1C2)]

Quality factor = SQRT(R1R2C1C2) / (R1C2 + R2C2)

The component value of R1 should contain the quadrature detector output resistance.

VCC

QUAD OUT

47pF

4.255uH

Rdamp

3

5

QUAD IN

BUF IN

BUF OUT

R1

R2

C2

C1

Vin

Vout

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