Transmitter; Common If; Cellular Band; Power Control - Nokia NKC-1X Series Technical Documentation Manual

NKC-1X
System Module
Two VHF synthesizers consist of: RX VHF Synthesizer includes integrated PLL and VCO
and external loop filter and resonator. The output of RX-VHF PLL is used as LO signal for
the second mixer in receiver. TX VHF Synthesizer includes integrated in TACO.

Transmitter

The transmitter RF architecture is up-conversion type (desired RF spectrum is low side
injection) whit (RF-) modulation and gain control at IF. The IF frequency is 180.54MHz.
The cellular band is 824.01-848.97MHz.

Common IF

The RF-modulator is integrated with PGA (Programmable Gain Amplifier) and IF output
buffer inside TACO_T RFIC-chip. I- and Q-signals, that are output signals from BB-side
SW IQ-modulator, have some filtering inside Safari before RF-modulation is performed.
The required LO-signal from TXVCO is buffered with phase sifting in TACO. After modula-
tion (π/4 DQPSK or FM) the modulated IF signal is amplified in PGA.

Cellular Band

At operation in cellular band the IF signal is buffered at IF output stage that is enabled
by TXP1 TX control. The maximum linear (balanced) IF signal level to 50Ω load is about –
8 dBm.
For proper AMPS-mode receiver (duplex)sensitivity IF signal is filtered in SAW-filter
before up-conversion. The upconverter mixer is actually a mixer with LO and output
driver being able to deliver about +6dBm linear output power. Ther mixer is inside TAC RF
IF. Note, that in this point, term linear means –33dB ACP. The required LO power is about
–6dBm. The LO signal is fed from TACO.
Before power amplifier RF signal is filter in band filter. The typical insertion loss is about
–2.7dB, and maximum less than –3.0dB. The input and output return losses are about –
10dB.
Power amplifier is 50Ω/50Ω module. It does not have own enable/disable control signal,
but it can be enabled by bias voltage and reference bias current signals. The gain window
is +27 to +31dB and linear output power is +30dBm (typical condition) with –28dB ACP.
The nominal efficiency is 50%.

Power Control

For power monitoring there is a power detector module (PDM) build up from a coupler, a
biased diode detector and an NTC resistor. RF signals from both bands are routed via this
PDM. The RF isolation between couplers is sufficient not to loose filtering performance
given by duplex filters.
The diode output voltage and NTC voltage are routed to BB A/D converters for power
control purpose. The TX AGC SW takes samples from diode output voltage and compares
that value to target value, and adjust BB I-and Q-signal amplitude and/or TACO PGA set-
tings to keep power control in balance.
Page 52
Nokia Corporation
CCS Technical Documentation
Issue 1 02/03