User Guide

PAMS
Technical Documentation
WinTesla User Guide
NHD–4
Page 44
Original 11/97
Aux. AGC Tuning
The purpose of this tuning operation is to calibrate the Automatic Gain
Control circuit in CDMA mode.
This tuning is needed if CDCONT (N201), N1, N2, N100 or N700 is
changed.
Aux. AGC is an auxiliary transmitter gain control feature implemented to
improve the signal to noise ratio of the CDMA TX output. The figures
below will assist in the explanation of the Aux. AGC functionality.
The gain of the CDMA transmitter is controlled by two devices, the
CDAGCT IC (N100) and the AT–109 variable attenuator (V106). CDMA
TX output power is controlled by the CDAGCT IC across the dynamic
range of –50 dBm to 15 dBm. The 15 dBm output point is referred to as
the Switch Point. Above the Switch Point (15 dBm), the AT–109 variable
attenuator controls the output power level. This secondary gain control
mechanism is referred to as Auxiliary AGC (Aux. AGC). A more thorough
description of Auxiliary AGC is found in the Transmitter Troubleshooting
Manual and Functional Description.
Below the Switch Point (less than 15 dBm CDMA TX power) the
attenuation of the AT–109 is set to its maximum level of tuned attenuation.
Above the Switch Point this attenuation is decreased, thus increasing the
overall gain of the CDMA TX chain. The Aux. AGC circuit is tuned to
provide a 10 dB dynamic range of attenuation. Without this 10 dB of
attenuation in place the output power increases 10 dB above the switch
point to approximately 25 dBm. In practice the 25 dBm may not be
reached due to the TX Gain Limiting feature. Figure 5.4.1 below depicts
this functionality.
The amount of attenuation provided by the AT–109 (V106) is controlled by
the voltage VC. VC is a function of the AGC_REF PDM. For minimum
attenuation the AUX. AGC PDM voltage is typically 0.75 V, resulting in
3.25 V for VC. For maximum attenuation the AUX. AGC PDM voltage is
typically 10.0 mV, resulting in 1.50 V for VC. The Auxiliary AGC can be
manually adjusted using the AGC_REF PDM controls found in the Service
Software.