Motorola P8190 Service Manual download pdf (Page 106)

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P8190: VCO/Vibrator

Description

U306 is the local oscillator module used to add frequency selectivity to the transceiver. The frequency of oscillation is dependent on the channel 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 frquency of U306 by varying the

voltage level to the input of U306.

The output of U306 is split into two paths. One path is used to feed back the produced signal to U110. The signal is prescaled and sent through a phase lock loop circuit

for frequency locking. The second path is sent to the receive circuit for carrier signal removal.

U306 will oscillate at a frequency of 112.32+RX freuqency.

The vibrator is driven by Q1711. U1800 sends a vibrator on signal, via VIB_ON, to Q1710. Q1710 will trun on Q1711 thus allowing B+ supply the VIB_DRIVE line.

Q1712 is configured as a diode and it's used to prevent the VIB_DRIVE line from going to a negative state.

VIB_DRIVE

VIB_ON

B+

Q1710

Q1711

U306

RX_CP_OUT

RX_SF

RXPRE_IN

RX_VCO

Q1712