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Motorola Confidential Proprietary
TDMA Timeport™ P8190
General Description
78
VCO
Merlin IC
VCO
The VCO is a local oscillator module used to
add frequency selectivity to the transceiver.
The frequency of oscillation is dependent on
the channel and band that the trans-ceiver
will be operating in. The frequency is con-
trolled by the Custom IC. The Custom IC will
receive channel information via the SPI bus
and adjust the frequency of the VCO by vary-
ing the voltage level to the input of the VCO.
The output of the VCO is split into two paths.
One path is used to feed back the produced
signal to the Custom IC. Then 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 sig-
nal removal.
TX Offset Oscillator
The offset oscillator frequency is controlled
by the Custom IC via TXCP_OUT. The oper-
ating frequency will depend on the dc bias-
ing of CR300. The offset oscillator frequency
is 157.32MHz in analog mode, and
112.32MHz in digital mode.
The LP_Switch, which comes from the Cus-
tom IC pin 40, changes the offset frequency.
The LP_Switch is on in analog mode and off
digital mode. The LP-Switch is currently not
supported in the TDMA StarTAC, therefore,
the frequency of the offset oscillator will be
157.32MHz regardl ess of whether it is in a
nalog or digital mode.
In analog mode the FM signal comes from
the DCI pin 39 and is modulated directly in
the offset oscillator. The offset oscillator with
the FM then enters QMOD. The Quadmod
will feed back the offset frequency to the
Custom IC for proper PLL operation.
The Merlin IC is a TX modulator. It takes
the TX information and modulates it on a
carrier for RF transmission. In analog mode
the offset oscillator with the FM enters the
Merlin IC and gets mixed with the main
VCO. The resulting signal is a differential
carrier with the modulated information. The
carrier is then passed through an IQ modu-
lator.
The A_D line controls the state of the IQ
modulator. In analog mode, the IQ modula-
tor simply feeds the carrier through to a volt-
age controlled amplifier(VCA). The gain of
the VCA is controlled via the AOC_CNTL
line, therefore, controlling the TX power
steps of the transceiver. Once the carrier
passes through the VCA, it passes through
the cellular final power amplifier which is
still internal to the Merlin IC
.
In digital mode the offset oscillator doesnt
contain the modulated information from the
FM line. The offset oscillator is mixed with
the main VCO and a differential out-put sig-
nal is sent through the IQ modulator. In digi-
tal mode, the A_D line configures the IQ
modulator to allow IQ modulation to the car-
rier. The result carrier signal is then passed
through the Voltage Controlled Amplifier
(VCA). The gain of the VCA is adjusted by
the AOC_CNTL line, thus controlling the TX
digital power steps of the transceiver. The
carrier is then routed through the cellular
final power amplifier and out to the trans-
mit circuit.
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