ADC

FB

OUT

LMV232

RFB

+

-

OFF

RF SIGNAL

BS

RFIN2

RFIN1

X

2

LMV232

www.ti.com

SNWS017C – DECEMBER 2004 – REVISED MARCH 2013

Figure 27. Strategy 3: Calibration during normal operation

The calibration measurement procedure can be explained with the aid of Figure 21, which depicts a typical power

measurement setup using the LMV232. In normal operation, the two PA’s in the setup will never be active at the

same time. One PA will produce the required transmit power, while the other one is off, (disabled) and produces

no power. The pedestal voltage should be measured in the absence of RF power. This can be achieved by

switching the Band Select (BS) pin such that the LMV232 input is selected where the disabled PA is connected

to. The pedestal voltage at no input power can be read at the output pin.

Using the Band Select (BS) control pin of the LMV232:

•

Select the RF input that is connected to the disabled PA, by the BS pin.

•

Measure the detector output.

•

Store the result in the phone memory.

•

Subtract the stored value from each detector power reading, until a new update is performed.

Important advantages of this approach are that no factory trim is required and the temperature drift of the

pedestal can be cancelled almost completely as well as the part-to-part spread. The remaining error is

determined by the resolution of the ADC. A slight disadvantage is that on average more than one detector

reading is required per power measurement. This overhead though can be made almost negligible in normal

circumstances.

Copyright © 2004–2013, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Links: LMV232