TDMA T2290/T2297:
VCO
B8
Description
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 ciruit ry 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 filte r 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 conditi ons R893 will not be grounded. This will decrease the loop filter bandwidth by increasing the
amount of resistance at the discharge path of C884.
VCO_STEER
RX_SF
VCO_FDBK
VCO_OUT
LP_SW
Filter Ckt.
Q880
A
Q880
B
U306
LP
Filter
RXCP_ADA
Summary of Contents for T2290
Page 1: ...DIGITAL WIRELESS TELEPHONE Service Manual Level 3 Release 1 TDMA T2290 T2297 ...
Page 26: ... 2000 Motorola Inc TDMA T2290 T2297 Cellular Overview 16 ...
Page 40: ...Motorola Confidential Proprietary TDMA T2290 T2297 TDMA Test Mode NAM Programming 30 ...
Page 68: ...Disassembly TDMA T2290 T2297 Keypad Removal Motorola Confidential Proprietary 58 ...