> 2.3 | Power Losses and Voltage Drops for GSM/GPRS

> Siemens wireless modules are specified to operate with specific voltage supplies. Voltage supplies may for instance range from 3.2V to 4.5V as measured on the module’s power connector.
> When consuming as much as 2…3A peak current, voltage losses due to stray resistances occur. Resistances occur in various parts, but there are three main areas to take into account.

> • | Impedance/resistance in the power source

> • | Resistance on connectors

> • | Resistance in signal tracks and lines

> Assuming that the total resistance in the power supply line is 50mOhm and that the resistance in the ground line is the same, this amounts to a total resistance of 100mOhm (0.1 Ohm). Calculating the voltage drop over the power supply line results in 200mV. To be on the safe side, it should be assumed that the voltage drop during the Tx burst does not exceed 400mV. This means that if the data sheet states a minimum voltage supply of 3.2V for a wireless module, the power supply solution should provide at least 3.6V.
> Figure 2: Voltage drop and ripple