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 (T101) connected between the first input terminal (V IN+ ) and the first terminal of the bridge output; - a second transistor (T102) connected between the second input terminal (V IN- ) and the first terminal of the bridge output; - a third transistor (T103) connected between the first input terminal (V IN+ ) and the second terminal of the bridge output; - a fourth transistor (T104) connected between the second input terminal (V IN- ) and the second terminal of the bridge output; wherein - the gate (G101) of the first transistor (T101) and the gate (G104) of the fourth transistor (T104) are connected to the first input terminal (V IN+ ); and - the gate (G102) of the second transistor (T102) and the gate (G103) of the third transistor (T103) 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 (T101) connected between the first input terminal (V IN+ ) and the first terminal of the bridge output; - a second transistor (T102) connected between the second input terminal (V IN- ) and the first terminal of the bridge output; - a third transistor (T103) connected between the first input terminal (V IN+ ) and the second terminal of the bridge output; - a fourth transistor (T104) connected between the second input terminal (V IN- ) and the second terminal of the bridge output; wherein - the gate (G101) of the first transistor (T101) and the gate (G104) of the fourth transistor (T104) are connected to the first input terminal (V IN+ ); and - the gate (G102) of the second transistor (T102) and the gate (G103) of the third transistor (T103) 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 (T101) connected between the first input terminal (V IN+ ) and the first terminal of the bridge output; - a second transistor (T102) connected between the second input terminal (V IN- ) and the first terminal of the bridge output; - a third transistor (T103) connected between the first input terminal (V IN+ ) and the second terminal of the bridge output; - a fourth transistor (T104) connected between the second input terminal (V IN- ) and the second terminal of the bridge output; wherein - the gate (G101) of the first transistor (T101) and the gate (G104) of the fourth transistor (T104) are connected to the first input terminal (V IN+ ); and - the gate (G102) of the second transistor (T102) and the gate (G103) of the third transistor (T103) 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. <EOS>