U306 is the local oscillator module used to add frequency selectivity to the transceiver. The frequency of oscilla tion is dependent on the channel and frequency band that

the transceiver will be operating in. The frequency is controlled by U110. U110 will receive channel information via the SPI bus and adjust the frequency of U306 by

adjusting the voltage level to the input (VCO_STEER) of U306.

The output of U306 is split into two paths. One path (VCO_FDBK) is used to feed back the generated signal to U110. The signal is prescaled and sent through a phase

detector for proper frequency locking. The second path (VCO_OUT) is sent to the front end IC(U10). This signal is used for proper downconversion of the receive signa l.

When the transceiver is operating in the 800MHz band, U306 will oscillate at a frequency of 112.32+RX frequency. In the 1900MHz band, U306 will oscillate at a fre-

quency of (112.32+RX)/2.

RX_SF (Super Filter) comes from U110 and provides a clean supply voltage to the VCO module.

LP_SWITCH control comes from U110. In Analog mode, the input to Q880 becomes high causin g it to switch on. This condition will complete the filter circuit path

to ground, thus allowing the filter ciruitry to become active on the VCO_STEER line. This filter circuit is used to improve phase noise due to stringent adjacent channels

in Analo g mode.

The RXCP_ADA is a loop filter adapt output. During a high current state R893 will be grounded. This will increase the loop filter bandwidth by decreasing the amount

of resistance at the discharge path of C884. During low curent conditions R893 will not be grounded. This will decrease the loop filter bandwidth by increasing the

amount of resistance at the discharge path of C884.

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