ADC

-

+

FB

OUT

+

LMV232

VREF

RFB

IOS

IDET

+

-

-

+

FB

OUT

+

LMV232

VREF

RFB

IOS

IDET

LMV232

www.ti.com

SNWS017C – DECEMBER 2004 – REVISED MARCH 2013

Figure 24. Pedestal Voltage

For low input power levels, the pedestal variation VPEDESTAL is the dominant cause of error. Besides temperature

variation of the pedestal voltage, which limits the lower end of the range, the pedestal voltage can also vary from

part-to-part. By applying a suitable measurement strategy, the pedestal voltage error contribution can be

significantly reduced or eliminated completely.

POWER MEASUREMENT STRATEGIES

This section describes the measurement strategies to reduce or eliminate the pedestal voltage variation. Which

strategy is chosen depends on the possibilities for a factory trim and implementation of calibration procedures.

Since the pedestal voltage is the reference level for the LMV232, it needs to be calibrated/measured at least

once to eliminate part-to-part spread. This is required to determine the exact detector output signal. Because of

process tolerances, the absolute part-to-part variation of the output voltage in the absence of RF input power will

be in the order of 5 - 10%. All measurement strategies discussed eliminate this part-to-part spread.

Strategy 1: Elimination of Part-to-Part Spread at Room Temperature Only

In this strategy, the pedestal voltage is determined once during manufacturing and stored into the memory of the

phone. At each power measurement this stored pedestal level is digitally subtracted from the measured output

signal of the LMV232 during normal operation. The procedure is thus:

•

Measure the detector output in the absence of RF power during manufacturing.

•

Store the output voltage value in the cell phone memory (after it is analog-to-digital converted).

•

Subtract the stored value from each detector output reading.

Figure 25. Strategy 1: Room Temperature Calibration

Copyright © 2004–2013, Texas Instruments Incorporated

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