T2801 datasheet(13/27 Pages) ATMEL

13 / 27 page

T2801

Preliminary Information

Rev. A9, 11-Dec-01

13 (27)

Functional Description

Receiver

The RF signal at RF_IN is fed to an image rejection mixer

IR_MIXER with its differential outputs MIXER_OUT1

and MIXER_OUT2 driving an IF-SAW filter at

110.592 MHz

112.32 MHz. The IF amplifiers

IF_AMP1 and IF_AMP2 with an external IF_TANK and

an integrated RSSI function feed the signal to the

demodulator DEMOD working at f = fIF/2 (

[55 MHz)

and finally to an integrated baseband filter BB. For

demodulator tuning in production an integrated 5-bit dig-

ital-to-analog (D/A) converter is provided to control the

on-chip varicap diode.

Transmitter

The transmit data at TX_DATA is filtered by an integrated

Gaussian Filter GF and fed to the fully integrated VCO

operating at twice the output frequency. After modulation

the signal is frequency-divided by 2 and fed via a TX/RX

SWITCH to the TX_DRIVER. This bus-controlled driver

amplifier supplies typical +3 dBm output power at

TX_OUT. A ramp-signal generator RAMP_GEN, pro-

vides a ramp signal at RAMP_OUT for the external power

amplifier, is integrated. The slope of the ramp signal is

controlled by a capacitor at the RAMP_SET pin.

Synthesizer

The

IR_MIXER,

the

TX_DRIVER

and

the

programmable counter PC are driven by the fully

integrated

VCO (including on-chip inductors and

varactors). An 3-bit digital-to-analog converter is used to

pretune the frequency. The output signal is frequency-

divided

to supply the desired frequency to the

TX_DRIVER, 0/90 degree phase shifter for the

IR_MIXER and to be used by the PC for the phase detec-

tor PD (fPD = 3.456 MHz). Unlimited multislot operation

is possible by using the integrated advanced closed-loop

modulation

concept

based

the

modulation

compensation circuit MCC.

Power Supply

An integrated bandgap-stabilized voltage regulator for

use with an external low-cost PNP transistor is imple-

mented. Multiple power-down and current saving modes

are provided.

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