Gsm Transmitter - Nokia RM-42 Service Manual

RM-42
System Module Nokia Customer Care
Another function of the detector voltage is to steer the DC/DC converter, which is providing a variable supply
voltage for the WCDMA PA.
WCDMA PA module
WCDMA PA is housed in a separate module having
• a variable supply voltage input for the amplifier stages (Vcc11),
• a battery supply voltage for the bias circuits (Vcc12),
• and two bias current inputs.
Bias currents are generated by 5-bit DA converters in N7501 RF ASIC. The converters are controlled by BB via
RFBus.
In production the PA quiescent current is set according to PA vendor's specifications. If another PA is changed
to the phone, this setting must be set again.
The bias currents are also used as PA on/off controls. The structure of the WCDMA PA is shown in the following
figure. The supply voltage for the output stage is got from a DCDC converter in order to improve the efficiency
at low power levels.
PA DCDC converter
The control of the DCDC converter is fed back from the power detector circuit.
The DCDC converter limits the lowest supply voltage to 1.5 V. At highest power levels the DCDC converter output
settles nominally to 3.2 V.
Figure 124 Block diagram of DCDC converter and WCDMA PA

GSM transmitter

An analogue IQ modulated signal is received to N7501 from digital BB.
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