Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1996-04-29
1997-08-05
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
G01J 500
Patent
active
056545509
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a signal processor for pyroelectric infrared sensor suitable for amplification of output signals of a pyroelectric infrared sensor or sensors.
BACKGROUND ART
Generally, the so-called pyroelectric infrared sensors have been known and in use as infrared sensors for detection of infrared radiations from a heating element. Such pyroelectric infrared sensors employ an infrared detection element of a pyroelectric material such as lead titanate (PbTiO.sub.3) or the like which is capable of producing pyroelectric effects. Namely, a pyroelectric element has properties such that, when subjected to a temperature change, for example, when heated by infrared rays incident on its surface, it loses electrical stability and produces charge due to spontaneous polarizations which turn a neutral state of charge into an electrically unbalanced state. Since pyroelectric material has an extremely high impedance, e.g., as high as several hundreds G.OMEGA., the charge produced in an infrared detection element can be picked up as a voltaic output signal by the use of an impedance transformer.
Illustrated by way of example in FIG. 14 are an infrared detection element and an impedance transformer circuit in a prior art infrared sensor.
In this figure, indicated at 101 is a pyroelectric infrared sensor which is constituted by an infrared detection element 102 and an impedance transformer circuit 103. The just-mentioned impedance transformer circuit 103 consists of a field-effect transistor (FET) 104 having its gate terminal connected to the output of the infrared detection element 102, a gate resistor Rg connected between the gate terminal of FET 104 and ground, and a drain resistor Rd connected between the drain terminal of FET 104 and ground. FET 104 is supplied with a source voltage Vcc at its source terminal, delivering at its drain terminal an output signal Vs from the pyroelectric infrared sensor 101.
In this instance, the output signal Vs of the impedance transformer circuit 103 consists of two components (AC and DC components), more specifically, a weak AC signal from the infrared detection element 102 and a DC signal attributable to the nature of FET 104.
Illustrated in FIG. 15 is a prior art signal processor circuitry which, has been conventionally resorted to for amplification of output signal Vs of a pyroelectric infrared sensor.
As seen in this figure, the signal processor is arranged as an inverting amplifier circuit 111 including an OP AMP (operational amplifier) 112, a coupling capacitor Ca and an input resistor ra connected in series between an inverting input terminal of the OP AMP 112 and an input terminal T1 of the inverting amplifier circuit 111, and a negative feedback resistor rb connected between output terminal and inverting input terminal of OP AMP 112. The noninverting input terminal of OP AMP 112 is grounded.
The output signal Vs of the infrared sensor 101 is fed to the input terminal T1 of the inverting amplifier circuit 111 as an input signal Vin, which input signal Vin being fed to the inverting input terminal of OP AMP 112 through a series circuit of the coupling capacitor Ca and input resistor ra for removing DC components therefrom.
OP AMP 112 has its output terminal T2 connected to its inverting input terminal through the negative-feedback resistor rb. The output voltage Vout can be defined as in Expression 1 below where f is the frequency of the input signal Vin. ##EQU1##
As clear from Expression 1 above, the smaller the frequency (f) of the input signal Vin, the smaller become the amplification factor and the output voltage Vout. Therefore, in order to use the inverting amplifier circuit 111 at a predetermined amplification factor, it is necessary for the input frequency (f) to be in a limited bandwidth.
In this regard, irrespective of the frequency (f) of the input signal Vin, it is conceivable to obtain a predetermined amplification factor through the inverting amplifier circuit 111 by increasing the resistance of the input resistor ra to a much grea
REFERENCES:
patent: 4263585 (1981-04-01), Schaefer
patent: 4808822 (1989-02-01), Manning et al.
patent: 4973843 (1990-11-01), Murata et al.
Nomura Tadashi
Yamazaki Shigeo
Hannaher Constantine
Murata Manufacturing Co. Ltd.
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