AN3249 datasheet(2/7 Pages) STMICROELECTRONICS

Part #	AN3249

Description	M24LR series internal capacitance considerations for antenna tuning

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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Tuning capacitance variation as a function of input voltage

AN3249

2/7

DocID017760 Rev 2

Tuning capacitance variation as a function of input

voltage

Figure 1 shows an example measurement of the M24LR serial equivalent capacitance as a

function of the VAC0-AC1 input RF voltage. The capacitance is measured between 0.2 VPEAK

and 2 VPEAK at 13.56 MHz using a network analyzer.

Figure 1. M24LR64-R serial equivalent capacitance CS measurement example

The dotted line in Figure 1 corresponds to the voltage level (0.5 V) at which the serial

capacitance (CS) of the M24LR series is measured in production and specified in the

datasheet (27.5 pF).

This voltage level has been chosen on the plateau of the capacitance curve to ensure the

best measurement repeatability.

M24LR series capacitance for antenna tuning

3.1

M24LR series equivalent schematic

Figure 2 shows the equivalent circuit of an M24LR mounted on a loop antenna, in the

presence of a magnetic field.

AN3249 Datasheet(PDF) 2 Page - STMicroelectronics