WE2408 View Datasheet(PDF) - Unspecified
Part Name
Description
MFG CO.
'WE2408' PDF : 36 Pages View PDF
WiNEDGE & WiRELESS
Winceiver WE2408
2.4GHz Single Chip FM Transceiver
The VCO center frequency is determined by an external tank circuit comprised of two inductors
connected to the TVCO pins 15 and 16. An external PLL loop filter network, connected to TPLL, pin
13, filters the VCO control voltage. This control voltage (KVCO 23 MHz/V for 800MHz) is used to tune
the tank frequency of the VCO via an internal, common-anode, varactor pair.
The transmit frequency for the WE2408 is programmed via serial interface (Data, Clock, and Load
Enable).
PA
The on-chip RF power amplifier is a differential gain stage capable of transmitting RF output power up
to -4dBm.
The differential output impedance is ~ -19://1pF at 2.4GHz. In the simplified application circuit shown
in page 3, a discrete LC network is used to match the output impedance to 50: at 2.4GHz ISM band.
The 27: resistor set the output power to ~ -4dBm.
REFERENCE OSCILLATOR
Crystal Oscillator and Reference Synthesizer
The reference synthesizer is comprised of an 11 bit counter which provides the PLL reference
frequency for both the receiver and transmitter synthesizers. A crystal oscillator circuit normally
provides the input to the reference synthesizer; however, external frequency source can be used as a
reference for the synthesizer. All 11 bits of the synthesizer are fully programmable, to allow a large
degree of flexibility in the choice of either the reference crystal or external reference frequency.
This reference oscillator can be kept active when both Tx and RX are off, by programming the Mode
Register, hence, reduce turn-on time for Tx or Rx.
AFC
Automatic Frequency Control (AFC) of the receive local oscillator (LO) frequency is used to improve
receiver performance. Without AFC, frequency offset (between receive signal and LO) causes a
reduction in SINAD due to filter distortion and beat tone. The AFC minimized the offset by tuning the
reference crystal oscillator. As a result, both transmit frequency and the receive LO are corrected at
the same time.
The AFC correction signal is available as a DC current at the AFC output (pin 46). A varactor,
connecting to the AFC output and the reference crystal, provides the required tuning action.
See section on AFC for more details.
© 2003 WiNEDGE & WiRELESS PTE LTD
Rev Date: 2003 May 23
Page 9
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