Tdk Corporation

Atsuko Tsuchida

Shiro Nakagawa

Eiji Takahashi

Takehiro Imai

Taisuke Domon

Kenji Aizawa

An oscillator circuit includes a gate G.sub.11 of C-MOS type (Q.sub.1, Q.sub.2, and the like) having the function of increasing an operating current i with increasing operating frequency. A humidity sensor HS changing electric impedance thereof in accordance with humidity is arranged in part of the oscillator circuit. The oscillator circuit converts a change in humidity into a change in frequency, causes the gate G.sub.11 to convert the change in frequency into a change in operating current i, and outputs the converted change in operating current i. Further, in order to increase the change in operating current i due to the change in frequency, a series circuit consisting of a capacitor C.sub.13 and a resistor R.sub.17 is connected to the gate G.sub.11 as a capacitive load.

Humidity meter

An absolute humidity meter in which a humidity sensor changes an electrical impedance thereof-exponentially with respect to the relative humidity. A z-f converting circuit (impedance to frequency ) generates a pulse signal corresponding to the impedance. A time constant control differentiating circuit has an impedance of a voltage control variable impedance element changed exponentially by a control voltage, and outputs a differentiated signal obtained by differentiating the pulse signal. A waveform shaping circuit outputs a pulse signal train obtained by binary-valued the differentiated signal. An integrating circuit causes a first integrating circuit to obtain the control voltage by integrating the pulse signal train and a second integrating circuit to obtain an output voltage of a relative humidity signal by integrating the pulse signal train, and obtains an absolute humidity signal by causing at least one of these integrating circuit to control the control voltage or the output voltage with increasing temperature.

Absolute humidity meter

A humidity sensor 1 has an impedance Zs thereof changed exponentially with respect to a relative humidity. A z-f conversion circuit 2 generates a pulse signal S1 corresponding to the impedance Zs. A time constant controlled differentiating circuit 3 has an impedance Zt of a voltage control variable impedance element 32 changed exponentially by a control voltage Vc, and outputs a differentiated signal S2 obtained by differentiating the pulse signal S1. A waveform shaping circuit 4 outputs a pulse signal train S3 obtained by binary-coding the differentiated signal S2. An integrating circuit 5 causes a first integrating circuit 51 to obtain the control voltage Vc by integrating the pulse signal train S3 and causes a second integrating circuit 52 to obtain a humidity signal S4 by integrating the pulse signal train S3. A bias circuit 6 applies a bias voltage to a control terminal 323 of the voltage control variable impedance element 32.

A humidity meter includes a humidity-frequency converter (2) which is essentially a pulse oscillator, the oscillation frequency of which depends upon the impedance of a humidity sensor (1), a differentiation circuit (3) and a wave-form shaping circuit (4) which essentially operate as a pulse width modulator for adjusting pulse width of an output pulse of the converter (2) for assuring a linear relationship between humidity and the output signal, and an integrator (6) for integrating the output of the pulse width modulator to provide an output signal as a DC level. A feedback path (5) is provided to apply the output signal to the pulse width modulator for assuring a linear output irrespective of the exponential characteristics of the humidity sensor. Said differentiation circuit (3) has a capacitor (31), a first variable impedance element (32) which is controlled by said feedback path , and a second variable impedance element (33) coupled in series with the first variable impedance element (32).

An A/D converter system has an A/D converter element (10) which provides a first predetermined number of digital output bits for each input analog signal. An addition device (12,70) adds linear slope potential to the input analog signal. A calculator (14) provides an average of a plurality of digital output signals of the A/D converter element so that the average has larger number of bits than the first predetermined number. The addition device is implemented by a time constant circuit (70) which functions as an integral circuit for an input analog signal, and functions as a differential circuit for a slope potential.

Analog to digital converter system

A humidity meter includes a humidity-frequency converter which is essentially a pulse oscillator, the frequency of which depends upon the impedance of a humidity sensor, a pulse width modulator for adjusting pulse width of an output pulse of the converter for assuring a linear relationship between humidity and the output signal, and an integrator for integrating the output of the pulse width modulator to provide an output signal as a DC level. A feedback path is provided to apply the output signal to the pulse width modulator for assuring a linear output irrespective of the exponential characteristics of the humidity sensor.

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Saitama, Japan

Atsuko Tsuchida