WE2408 Просмотр технического описания (PDF) - Unspecified

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WE2408

2.4GHz Single Chip FM Transceiver

Unspecified 

WiNEDGE & WiRELESS

Winceiver WE2408

2.4GHz Single Chip FM Transceiver

FUNCTIONAL DESCRIPTION

The receive section consists of several major function blocks, including a switchable RF input

attenuator (PAD), quadrature down-conversion mixer, differential-to-single-ended conversion, variable

gain amplifiers (VGAs), PLL synthesizer/ voltage controlled oscillator (VCO), I/Q low-pass filters, DC

offset correction circuitry, quadrature up-conversion mixer, IF filter, P/D FM demodulator.

The transmit section consists of a PLL synthesizer, direct frequency modulated voltage controlled

oscillator (VCO), and a RF power amplifier (PA).

Additionally, the device contains a reference crystal oscillator, an automatic frequency control (AFC)

circuitry and associated reference frequency synthesizer.

A functional block diagram of the IC is shown in page 4. The following sections give details of each

functional block.

ZERO IF RECEIVER

The receiver section of the WE2408 utilizes a quadrature mixer in a direct-conversion, zero-

intermediate frequency (zero-IF) approach. After quadrature down-conversion and baseband filtering,

a quadrature mixer up-converts the complex baseband signal to an intermediate frequency (IF) for

demodulation.

Direct conversion to zero-IF has several advantages over super-heterodyne approaches. First, the

image frequency is eliminated because the IF is zero. Second, the use of active, low pass, filters

provide a high level of integration, while eliminating the need for external IF filters and IF

transformers.

A description of each major receive function block follows:

RF Input Attenuator Pad

A switchable 0/-10dB attenuator pad allows high signal level capability at the RF Input of the receiver.

This pad is located prior to the quadrature mixer (down-conversion) and can be either manually

controlled via the 3-wire interface, or automatically controlled via the AGC section of the device.

Down-Conversion Quadrature Mixer

The main advantage of the quadrature mixer is its ability to translate the RF frequency directly to a

zero-IF, thereby eliminating the image frequency. Consequently, the image filter before the RF input

to the WE2408 can be eliminated. The design requirements for the duplexer and RF band pass filter

may also be relaxed. In addition, the quadrature mixer achieves a lower overall noise figure by virtue

of image frequency elimination.

The balanced mixers in the quadrature mixer are designed to closely track each other in both

amplitude and phase response. The quadrature LO signal is generated by direct division of the

receive VCO, thereby eliminating external phase shifting networks. Furthermore, for improved noise

immunity, all internal RF signal paths are fully differential, thereby providing common mode noise

rejection. The gain of the mixer can be adjusted via the 3-wire interface programming or automatically

controlled by AGC.

© 2003 WiNEDGE & WiRELESS PTE LTD

Rev Date: 2003 May 23

Page 6

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