Abstract: A bias circuit (FIG. 5) of the type comprising a bias transistor (T1) having a pair of resistors (R1, R2) in its collector path, the junction of these two resistors (R1 and R2) being connected to the transistor base. The base of a drive transistor (T2), of like polarity type, is connected to the collector of the bias transistor (T1), this serving as current source or sink. To provide and increase extended operation, operation at supply voltages lower than usual and current regulation from low supply voltage (0.9V) to much high voltage, this circuit is modified by the provision of a third resistor (R3) in the collector path and a diode shunt (T3) between the base of the drive transistor T2 and the junction of the third and first resistors (R3 and R1). The polarity inverse of this modified circuit is also effective and may be combined, in cascade or in ring feedback loop configuration, with the aforementioned modified circuit. These latter combinations serve to provide yet higher order current regulation.

Abstract: A circuit (FIG. 4) in which a sub-circuit comprised of a bias transistor (T1), a feedback reisistor (R2) connected between the collector of this transistor (T1) and its base, and, a drive transistor (T2), is connected to its polarity-inverse sub-circuit (T1', R2', T2') in a ring configuration and is initiated by means of current injection from a start-up bias circuit. The latter may comprise a bias transistor (T1"), a drive transistor (T2") the base of which is connected to the collector of the bias transistor (T1"), and a pair of feedback current/voltage divider resistors (R1", R2") in the collector path of the bias transistor (T1"). Following start-up, constant current is maintained by feedback in the ring, and this current may be tapped at an appropriate point in the ring.

Abstract: A mixer receives a frequency shift keyed (FSK) radio signal having two transmission frequencies and mixes the radio signal with a first or a second local oscillator signal from a local oscillator to provide a mixed signal. The mixed signal lies within a high or low band of frequencies depending upon the frequency of the FSK signal and upon the local oscillator signal received by the mixer. A detector receives the mixed signal and detects in which band of frequencies the mixed signal lies, and generates a switching signal in dependence upon the band of frequencies in which the mixed signal lies. If the FSK signal changes to a different transmission frequency and this causes the mixed signal to lie in the low band of frequencies, then a switching signal is generated which switches the local oscillator such that the oscillator generates a different local oscillator signal which causes the mixed signal to shift to the high band of frequencies.

Abstract: A signal strength detector comprises first, second and third transistors of the same conductivity type. The emitter electrodes of each transistor are connected together and coupled with one of a pair of dc supply lines. The collector electrodes of the first and second transistors are each coupled with the other of the pair of dc supply lines. The base electrode of the first and second transistors are each coupled via a resistor to the base electrode of the third transistor. The collector electrode of the third transistor is effective to provide a source of output current which is representative of a differential signal level between the base electrodes of the first and second transistors.