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US 5,189,362 AGranted
High frequency signal measurement circuits utilizing temperature-sensitive devices
OwnerRichard G. V. Dobleinventor
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OwnerRichard G. V. Dobleinventor
Estimating the term…
A circuit for measuring the R.M.S. voltage of a high frequency signal (e.g. 100MHz) comprises two series-connected ntc thermistors (TH1, TH2) in a bridge circuit which is energized by a current source (1). The unknown signal is applied across one (TH1) of the thermistors and the resulting change in the resistance causes a D.C. output voltage to appear across the balanced terminals (T3, T4) of the bridge. This output voltage is proportional to the square of the R.M.S. voltage of the A.C. signal. In another embodiment, two ptc thermistors are connected in parallel in a bridge circuit which is energized by a voltage source, and are used to measure R.M.S. current. In each case, the thermistors are preferably operated in a negative slope resistance portion of their voltage-current characteristic. In a further embodiment two balanced bridges, each incorporating two thermistors, are connected in series in one arm of a bridge circuit, and a compensating signal is applied by a feedback circuit to one bridge so as to match the heating effect of the unknown A.C. signal applied to the other bridge.
A bridge circuit arrangement for measuring the amplitude of an A.C. signal, comprising first and second temperature-sensitive devices, said first temperature-sensitive device being incorporated in a balanced bridge circuit, power supply means coupled to said first and second temperature-sensitive devices and arranged to energise said balanced bridge circuit at a first balanced pair of terminals thereof, means for applying an A.C. signal to one of said temperature-sensitive devices and means for applying a compensating signal to the other of said temperature-sensitive devices, one of said signals being applied to said first temperature-sensitive device via a second balanced pair of terminals of said balanced bridge circuit and thereby isolated from the other of said signals, and feedback means coupled to said first and second temperature-sensitive devices, said feedback means being arranged to vary the amplitude of said compensating signal in relation to the amplitude of said A.C. signal so as to maintain a predetermined relationship between the amplitudes of said signals.
A circuit arrangement for measuring an A.C. signal, comprising a power supply arranged to generate a constant-current biasing signal, at least one temperature-sensitive device having a negative temperature coefficient of resistance and arranged to carry said constant-current biasing signal, said temperature-sensitive device having a pair of terminals and said biasing signal being arranged to generate a biasing voltage across said terminals, and means for superimposing said A.C. signal on said constant-current biasing signal carried in said temperature-sensitive device so as to vary the resistance of said temperature-sensitive device and thereby vary said biasing voltage across said terminals thereof in dependence upon the amplitude of said A.C. signal.
A circuit arrangement as claimed 7 wherein said temperature-sensitive device is a thermistor.
A circuit arrangement for measuring an A.C. signal, comprising a power supply arranged to generate a constant-voltage biasing signal across at least one temperature-sensitive device, said temperature-sensitive device having a positive temperature coefficient of resistance and said biasing signal being arranged to generate a biasing current in said temperature-sensitive device, and means for superimposing said A.C. signal on said biasing signal in said temperature-sensitive device so as to vary the resistance of said temperature-sensitive device and thereby vary said biasing current in dependence upon the amplitude of said A.C. signal.
Dependencies are inferred from the claim text.