differernt vco design for gsm

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【文件名】:06328@52RD_differernt vco design for gsm.pdf
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Introduction
The differential pair of bipolar transistors is the common
building block in modern RF integrated circuits. An
advantage of this architecture is its high loop gain making
it popular for differential Voltage Controlled Oscillator
(VCO) designs in RFICs. Designers of discrete (or hybrid)
VCO circuits usually use the more traditional Colpitts
design avoiding the added complexity of the differential
VCO configuration.
Because of its primary usage in proprietary RFICs, only
limited differential VCO design and modeling information
has been made available. In this application note, we will
attempt to build a bridge toward better understanding of
the differential VCO by describing a design covering
910–980 MHz which is appropriate for use in GSM
handsets. This design will also demonstrate how the
SMV1493-079 varactor diode, an essential element in this
VCO, may be used advantageously in designs aimed at
other wireless applications including AMPS, CDMA,
and PCS.