## Battery Voltage Measurement

The battery voltage is measured using RFI2, N450 A/D converter channel 0 and 7. The converter value supplied from channel 7 is measured when the transmitter is active. This measurement gives the minimum battery voltage. The value from channel 0 is measured when the transmitter is inactive. The battery voltage supplied to the A/D converter input is switched off when the baseband is in power off. The battery voltage measurement voltage is supplied by PSCLD, N301 which performs scaling, the scaling factor is R1(R1+R2), and switch off. The measurement voltage is filtered by a capacitor to achieve an average value that is not depending upon the current consumption behavior of the baseband. To be able to measure the battery voltage during transmission pulse the time constant must be short. The value for the filtering capacitor is set to 1 nF, C319. The scaling factor used to scale the battery voltage must be 1:3, which means that 9V battery voltage will give 3V A/D converter input voltage. The A/D converter value in decimal can be calculated using the following formula:

A/D = 1023xR1xU BAT/((R1+R2)xU ref) = 1023xUBATxK where K is the scaling factor. K = R1/((R1+R2)xUref).

System Module

Technical Documentation 