The offset oscillator frequency is controlled by U110(ZIF/SYN) via TXCP_OUT. The operating frequency will depend on the dc biasing of CR300. The offset oscillator

frequency is 157.32MHz in 800MHz mode, an d 192.36MHz in 1900MHz mode.

The two operating frequencies are controlled by the 800*_1900 line. A high state at 800*_1900 will switch Q351 on. This condition will bypass path to ground for C316,

thus C316 is not be active with the tank circuit. During this state, the TX offset oscillator will operate at 192.36MHz. A low state at 800*_1900 will switch Q351 off.

This condition will allow C316 to remain active with the tank circuit. Duri ng this state the TX offset oscillator will operate at 157.32MHz.

The TXCP_ADA is a loop filter adapt output. During a high current state R308 will be grounded. This will increase the loop filter bandwidth by decreasing the amount

of resistance at the discharge path of C303. During low curent conditions R308 will not be grounded. This will decrease the loop filter bandwidth by increasi ng the

amount of resistance at the discharge path of C303.

LP_SWITCH control comes from U110. In Analog mode, the input to Q301 becomes high causing 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.

In analog mode the FM signal comes from U1800(DCI) pin 39 and is modulated directly in the offset oscillator. The offset oscillator with the FM then enters U301

(QMOD). The Quadmod (U301) will fe ed back the offset frequency to U110 for proper PLL(Phase Locked Loop) operation.