A detector circuit for detecting a signal level of a radio-frequency signal, comprising: a sub-threshold transistor bridge circuit, comprising: - a first input terminal (V IN+); - a second input terminal (V IN-); - a bridge output, comprising a first and a second terminal; - a first transistor connected between the first input terminal (V IN+) and the first terminal of the bridge output; - a second transistor connected between the second input terminal (V IN-) and the first terminal of the bridge output; - a third transistor connected between the first input terminal (V IN+) and the second terminal of the bridge output; - a fourth transistor connected between the second input terminal (V IN-) and the second terminal of the bridge output; wherein - the gate of the first transistor and the gate of the fourth transistor are connected to the first input terminal (V IN+); and - the gate of the second transistor and the gate of the third transistor are connected to the second input terminal (V IN-); wherein the radio frequency signal is applied to the first input terminal (V IN+) and to the second input terminal (V IN-); the first, second, third, and fourth transistors are all n-channel MOSFETs; and each of the first, second, third, and fourth transistors is configured to operate in the sub-threshold region for a desired range of the signal level of the radio-frequency signal. a sub-threshold transistor bridge circuit, comprising: - a first input terminal (V IN+); - a second input terminal (V IN-); - a bridge output, comprising a first and a second terminal; - a first transistor connected between the first input terminal (V IN+) and the first terminal of the bridge output; - a second transistor connected between the second input terminal (V IN-) and the first terminal of the bridge output; - a third transistor connected between the first input terminal (V IN+) and the second terminal of the bridge output; - a fourth transistor connected between the second input terminal (V IN-) and the second terminal of the bridge output; wherein - the gate of the first transistor and the gate of the fourth transistor are connected to the first input terminal (V IN+); and - the gate of the second transistor and the gate of the third transistor are connected to the second input terminal (V IN-); wherein - a first input terminal (V IN+); - a second input terminal (V IN-); - a bridge output, comprising a first and a second terminal; - a first transistor connected between the first input terminal (V IN+) and the first terminal of the bridge output; - a second transistor connected between the second input terminal (V IN-) and the first terminal of the bridge output; - a third transistor connected between the first input terminal (V IN+) and the second terminal of the bridge output; - a fourth transistor connected between the second input terminal (V IN-) and the second terminal of the bridge output; wherein - the gate of the first transistor and the gate of the fourth transistor are connected to the first input terminal (V IN+); and - the gate of the second transistor and the gate of the third transistor are connected to the second input terminal (V IN-); wherein the radio frequency signal is applied to the first input terminal (V IN+) and to the second input terminal (V IN-); the first, second, third, and fourth transistors are all n-channel MOSFETs; and each of the first, second, third, and fourth transistors is configured to operate in the sub-threshold region for a desired range of the signal level of the radio-frequency signal.