Agc; Figure 19: Phase Control Loop - Nokia NSB-5 Series Technical Documentation Manual

PAMS Technical Documentation
detector is a multiple of the 13MHz VCTCXO (reference frequency is 200 kHz). Output of
the phase detector is connected to the charge pump, which charges or discharges the
integrator capacitor in the loop filter depending on the phase of the measured frequency
compared to reference frequency. The loop filter attenuates the pulses and generates a
DC voltage which controls the frequency of UHF VCO. This loop filter defines the step
response of the PLL (settling time), affects the stability of the loop and is used for side-
band rejection.
The VHF synthesizers contains a 16/17 dual modulus prescaler, a "N" and "A" divider, a
reference divide, a phase detector, a charge pump, a discrete VCO, and a lowpass filter.
The frequency of the VHF VCO is 800 MHz, which is frequency divided to 400 MHz and
100 MHz. Operation of the VHF PLL is similar to that of the UHF PLL. The VHF PLL using
the 400 MHz signal as its input frequency. The reference frequency in the VHF synthe-
sizer is 1 MHz.
f
ref
PHASE
DET.
f_out / M

AGC

The purpose of the AGC–amplifier is to maintain a constant output level from the
receiver. To accomplish this, pre–monitoring is used. This premonitoring is done in three
phases and this determines the settling times for the RX AGC. The receiver is switched on
approximately 150 ms before the burst begins, DSP measures the receive signal level and
adjusts the TXC–DAC (which controls Receive Controlled Gain Amplifier) or it switches
on/off the LNA with the FRAC control line. The Receive Controlled Gain Amplifier has
57 dB of continuous gain control (40 dB to –17 dB) while the gain in the LNA is a digital
step and is either 15 dB or –16 dB.
The requirement for receive signal level (RSSI) under static conditions is that the MS
shall measure and report to the BS over the range –48 dBm to –110 dBm. For RF levels
above –48 dBm, the MS must report to BS the same reading, so above this level the AGC
is not required. Because of the RSSI requirements, the gain step in LNA is "ON" ( FRAC =
"0") for receive levels below –48 dBm. This leaves the AGC in SUMMA to adjust the gain
Issue 1 03/01
freq.
reference
CHARGE
PUMP
Kd

Figure 19: Phase Control Loop

Nokia Mobile Phones Ltd.
System Module
VCO
Kvco
M=A(P+1) + (N–A)P
=NP + A
NSB-5
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