Integrated low power received signal strength indicator (RSSI) with linear characteristic
An RSS indicator with a linear characteristic that is of a simple configuration, low current consumption and small die area requirements, comprises a pair of input transistors with coupled emitters and base electrodes to which an input signal is differentially applied. Each of the input transistors has a collector load circuit connected between a first supply terminal and its collector, and a tail current sink connected between a second supply terminal and the coupled emitters. The load circuit of each input transistor includes a current source which supplies a current copied from the tail current. A signal strength indicator signal is obtained from a differential signal between corresponding output nodes of the collector load circuits by taking the mean value of the differential signal referenced to the first supply terminal.
1. A received signal strength indicator, comprising:
a pair of input transistors with coupled emitters and with base electrodes to which an input signal is differentially applied;
a collector load circuit associated with each input transistor, each collector load circuit including a first active device configured as a current source, connected between a first supply terminal and a collector of the respective input transistor, and including an output node; and
a tail current sink including a second active device connected between a second supply terminal and the coupled emitters;
wherein the first active device in each collector load circuit associated with each input transistor is adapted and configured to supply a current copied from the tail current; and
wherein a signal strength indicator signal is obtained from a differential signal between the corresponding output nodes of the collector load circuits by taking the mean value of the differential signal referenced to the first supply terminal.
2. The received signal strength indicator according to claim 1 , wherein the collector load circuit of each input transistor includes a resistor connected in parallel with the current source, and wherein the output node is the collector node.
3. The received signal strength indicator according to claim 1 , wherein the collector load circuit of each input transistor includes a common base connected transistor and a resistor connected in the collector path of the common base connected transistor, the common base connected transistor and resistor being connected in parallel with the current source; and the output node is the connection node between the resistor and the collector of the common mode connected transistor.
4. The received signal strength indicator according to claim 1 , wherein the collector load circuit of each input transistor includes a diode connected in series with a resistor, the diode and resistor being connected in parallel with the current source; and the output node is the connection node between the resistor and the diode.
5. The received signal strength indicator according to claim 1 , wherein the first active device configured as the current source in each collector load circuit is a MOS transistor connected as a current mirror.
6. A received signal strength indicator comprising:
a pair of input transistors with coupled emitters and with base electrodes to which an input signal is differentially applied;
a collector load circuit associated with each input transistor, each collector load circuit including a first active device configured as a current source, connected between a first supply terminal and a collector of the respective input transistor; and
a tail current sink including a second active device connected between a second supply terminal and the coupled emitters;
wherein the first active device in each collector load circuit associated with each input transistor is adapted and configured to supply a current copied from the tail current;
each collector load circuit includes a common base connected transistor having an emitter connected to the collector of the respective input transistor, the common base connected transistors having a common collector node which is connected to the first supply terminal through a load resistor, and a signal strength indicator signal is obtained from the common collector node as referenced to the first supply terminal.
7. The received signal strength indicator according to claim 6 , wherein the active device configured as the current source in each collector load circuit is a MOS transistor connected as a current mirror.
8. The received signal strength indicator according to claim 7 , comprising a circuit branch connected between the first and second supply terminals, the circuit branch including a MOS transistor connected to copy the tail current; and the MOS transistor in each collector load circuit being adapted and configured for mirroring the current in the circuit branch.
9. The received signal strength indicator according to claim 8 , wherein the tail current sink includes a MOS transistor, adapted and configured to be controlled by a same bias control voltage as the MOS transistor in the circuit branch.
10. The received signal strength indicator according to claim 1 , wherein the emitter circuits of the input transistors include a degeneration resistor.