Method for obtaining field strength information
A method for obtaining field strength information from a received electromagnetic signal by a receiver unit, in which an input voltage is generated for an operational amplifier from the received signal in the receiver unit by an input resistance and an output voltage is generated by the operational amplifier by a fixed amplification factor. The input voltage is changed until the output voltage lies within a predefined interval that includes the value of the reference voltage, and hereby the input voltage is tapped at a divider node of a voltage divider and to adjust the output voltage to the reference voltage the gate voltage of the MOS transistor, operating within a nonlinear range, and connected to the divider node is changed in such a way that the forward resistance of the MOS transistor is changed substantially logarithmically and the field strength value received by the receiver unit is determined from a comparison of the value of the present gate voltage with the quantities assigned to the gate voltage values in a memory.
1. A method for obtaining field strength information from a received electromagnetic signal via a receiver unit,
generating an input voltage for an operational amplifier from the received signal in the receiver unit via an input resistance;
generating an output voltage by the operational amplifier via a fixed amplification factor;
changing the input voltage until the output voltage lies within a predefined interval that includes a value of the reference voltage;
tapping the input voltage at a divider node of a voltage divider;
changing a gate voltage of a MOS transistor that is operating within a nonlinear range and connected to the divider node to adjust the output voltage to the reference voltage such that a forward resistance of the MOS transistor is changed in a nonlinear manner;
generating the gate voltage via a controllable current source and a controllable current sink such that a storage element connected to the gate of the MOS transistor is discharged or charged; and
determining a field strength value received by the receiver unit from a comparison of the value of a present gate voltage with quantities assigned to the gate voltage values in a storage element.
2. The method according to claim 1 , wherein, to adjust the operating point of the MOS transistor, the storage element is supplied with current from a constant current source.
3. The method according to claim 1 , wherein the storage element is discharged via a switch.
4. A circuit arrangement comprising:
a receiver unit configured to receive an electromagnetic signal;
an input resistance configured as a voltage divider, the input resistance having a divider node;
a voltage divider branch connectable to the divider node, the voltage divider branch including a MOS transistor linked to a reference potential, the MOS transistor having a control input for applying a gate voltage;
an operational amplifier having an input and an output and a fixed amplification factor, the input being connectable to the divider node and the operational amplifier being configured to supply an output voltage from a present input voltage; and
a control element connectable to an output of the operational amplifier and configured to provide a gate voltage for the MOS transistor from a comparison of the output voltage with a reference voltage,
wherein the MOS transistor has an operating point in the nonlinear range and is linked directly to the divider node and to the reference potential, so that a change in the input voltage to adjust the output voltage to the reference voltage solely based on a change in the gate voltage of the MOS transistor, and
wherein, to generate the gate voltage a storage element, a controllable current source and a controllable current sink are linked to the control input of the MOS transistor.
5. The circuit arrangement according to claim 4 , wherein the storage element is linked to a constant current source to set an operating point of the MOS transistor.
6. The circuit arrangement according to claim 4 , wherein a switch is linked parallel to the storage element to discharge the storage element.