JPS6140553A - Temperature measurement oscillation circuit - Google Patents

Abstract

PURPOSE:To obtain a synchronous pulse-like signal according to humidity, by providing a moisture-sensitive element in a feedback circuit of a feedback amplifier having on OR circuit, into which a control signal is inputted to control the oscillation of a feedback amplification circuit. CONSTITUTION:A feedback signalis applied into one input of an NAND gate G of an OR circuit through a resistor R1 and when a control signal Sc of 'H' is applied into the other input thereof from an input IN, the NAND gate G is turned ON to perform a oscillating operation while when that of 'L' is applied, the operation is stopped. The output of the NAND gate G is amplified inversely with a first complimentary push-pull amplifier while done so with a second complimentary push-pull amplifier through an inverter IN. A thermistor TH and a moisture-sensitive element CH varying in the electrostatic capacitance with the humidity are connected to feedback circuits from these outputs opposite in the phase to each other respectively. Thus, a pulse is outputted from an output OUT according to the charge and discharge of the moisture-sensitive element CH.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an oscillation circuit for humidity measurement that generates a pulse-like signal with a period corresponding to humidity.

[Prior art]

Previously, the "Temperature and Humidity Detection Device" was filed separately by the applicant.
(Utility Model Publication No. 54-32954'), a first inverter and a second inverter are connected in cascade, and a capacitor and a resistor are connected from the input of the first inverter to the output of the second inverter. After applying positive feedback through a series circuit of However, the oscillation frequency is controlled by a change in the resistance value of the temperature detection element according to the humidity, thereby obtaining a pulse signal having a frequency corresponding to the humidity. In this case, when high precision is required for humidity measurement, the oscillation frequency must be set high, and in order to process the sipulse signal by a digital circuit such as a processor, it is necessary to divide the frequency using a divider. In short, the configuration of the device becomes complex, which makes it expensive, and continuous oscillation causes problems such as temperature rise in the circuit elements and heat generation due to energization of the humidity detection element itself, which causes problems in measurement. This method has drawbacks such as the tendency for errors to occur.

In addition, a method is generally adopted in which a current is passed through the humidity detection element to detect a change in terminal voltage due to a change in the resistance value of the humidity detection element.In this case, when the detection output is processed by a digital circuit, analog - Requires a digital converter (hereinafter referred to as ADC), which has the same disadvantage of being expensive as described above.

[Summary of the invention]

The present invention has the purpose of fundamentally solving such drawbacks of the conventional art, and provides a feedback signal to one input of an AND circuit, and a control signal to the other input, thereby controlling the output of the AND circuit. each performs inverting amplification, exhibits low output impedance, and has outputs in opposite phases to each other;
and a second complementary push-pull amplifier,
The output of each amplifier is connected individually to one input of the AND circuit, and a humidity sensing element whose capacitance value changes depending on the humidity is inserted in series to either side of each feedback circuit. , and a temperature sensing element whose resistance value changes depending on the temperature is inserted in series into one of the other feedback circuits, and the start and stop of the oscillation operation is controlled by a control signal, and the periodicity is controlled according to the humidity. The present invention provides an extremely effective humidity measurement oscillation circuit that obtains a pulsed signal.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to figures showing examples.

Figure 1 is a basic circuit diagram.One input of a NAND gate G as an AND circuit is supplied with a feedback signal via a resistor R1, and the other input is supplied with a feedback signal via a resistor R1. is given a control signal Sa of @H# (high level) from the input IN, and the NAND gate G is turned on only during 'H#', threatening to perform oscillation operation, while this is 1L'' (low level). ), the NAND gate G is turned off, so
It is designed to stop the oscillation operation.

The output of the NAND gate G is connected to a first complementary push-pull amplifier (hereinafter referred to as C
PA), and is also inverted and amplified by the second CPA, which consists of resistors R4+R5, capacitors C3+C4, and transistors Q3 and Q4, via inverter IN. From each output having a phase opposite to each other, a thermistor TT (as a temperature sensing element) with a resistor R6 connected in parallel is inserted in series with a resistor R7 to the input of a NAND gate G via a resistor R1. Feedback is sent to each individual through a first feedback circuit, and a second feedback circuit in which a humidity sensing element cH whose capacitance value changes depending on humidity, such as the H1 type manufactured by Philips, is inserted in series. A signal is given.

However, transistor Q1. The output of CPA by Q2 is in phase with the input of NAND gate G, transistor Q3.
The output of CPA by Q4 is in opposite phase to the input of NAND gate G, and the thermistor TH and resistor R6r R7
The capacitance of the humidity sensing element cH is charged and discharged through the capacitor cpA, and the terminal voltage of the humidity sensing element cH is given as a feedback signal.The output impedance of each cpA is sufficiently low (NAND gate). ) It is possible to supply sufficient voltage and current necessary for input driving of G and charge/discharge driving of the humidity sensing element cH, as well as ground fault to a common potential.

Therefore, if the control signal So becomes H'', the humidity sensing element CH
The waveform of each part in FIG. 1 is shown in FIG. 2. The feedback signal (!L) changes according to the charging and discharging of the humidity sensing element CH, and this is the NAND game)
The waveform is shaped and inverted at the inverter IN to produce the output (b), which is further inverted by the inverter IN and becomes the output (C
) and is sent from the output OUT.

Also, for the outputs (b) and (e), the transistor (
The output of CPA by h+Q2 (a) and the output of CPA by transistor Qs+Q4 (,) are each inverted, output (d) is @H#, and output C@) is "L".
At the time of , the output (6
), and the resulting terminal voltages of the thermistor TH and resistors R6r to R7 are applied to the input of the NAND gate G as a feedback signal (a).

This feedback signal (a) is high at the beginning of charging the humidity sensing element cH, and decreases as the charging ends, and at the beginning, the output (b)
is @L'', but when the input response threshold voltage of NAND gate G decreases to VTI (output (b)
changes to 1H'', the output (d) changes to @L'' and the output (・) changes to ``H'', and at this time, the humidity sensing element cH
The voltage remaining as charge charge to @H# is the power supply voltage v
If it is equal to Dn, it becomes VDD -VTH, which causes the output (a) @L'' to use the positive side as the reference potential, so the feedback signal (a) changes in the negative direction until (VDD -VTR). Then, using this as a reference, the output (6) is charged in the opposite direction, and the terminal voltage of the humidity sensing element C becomes the feedback signal (a), and initially the output (b) becomes ``H''. "However, as the feedback signal (,) gradually rises and reaches the VTR, the output (b) reaches @L" and the output (e) reaches @H.
The output (a) changes to "H#" and the output (e) changes to "L", and at this time, the voltage V remaining as a charge on the humidity sensing element cH
The feedback signal (a) rises at Vnn + VTHi due to the sum of TR and VDD, and then the discharge and output (d
), the above operation is repeated.

In particular, each period of rise and fall of the feedback signal (a) due to charging and reverse charging of the humidity sensing element cH is expressed as tll.
t, the period T is given by the following equation.

T=t, -1-t.

However, RT: thermistor TH and resistor R6+K7
Combined resistance value CT: Capacitance value VTH of humidity sensing element cH: Input response slen τ of NAND gate G Hold voltage jVDD
: Since the power supply voltage is small, if vTH=1/2·vDD, equation (1) becomes the following equation.

T middle 1・IRT@C ding+1・IRT@CT=202RT
・CT ・Old...Yuyu...River...
(2) Therefore, if CT changes according to a fixed relationship depending on the humidity, humidity can be measured by detecting the period T by counting four pulses or the like.

Note that 1CT is expressed by the following equation.

CT=Kt CH+Kz(θ−θo))”+Kz(
H+K t (θ-06) )+Ks ・・・・・・・・・
...(3) However, Kl, 2. 3: Coefficient H: Humidity θ: Current temperature θ0: Reference standard In other words, CT depends on θ as well as H, and it is necessary to compensate for the variation of cT in response to temperature. The loss must be compensated for by the thermistor TH.

Therefore, if we find 8 guns, it is given by the following formula).

RT=(Ro-s scream-A7/Rs)+Rz mmmm
(4) However, Ro: Resistance value of thermistor 1 at reference temperature F: Coefficient/: (3) which shows parallel composition with 86, Equation (2) is taken from Equation (4).

・・・・・・・・・・・・・・・ (5) Therefore,
If the characteristics of the thermistor TH and the resistors R, , R, are determined according to the temperature characteristics of the humidity sensing element cH, humidity can be measured accurately.

In Fig. 1, each CPA is provided for feedback to the input of the NAND gate G and the inverter IN because the output impedance of the NAND gate G and the inverter IN is C-M.
OS (Comp@mentary-Metal O
xideSem1conductor, ), then 5
000 to several XΩ, and sufficient output voltage, current, and ground fault effect cannot be obtained, causing an error in the charging and discharging period of the moisture sensitive element CH, and the condition shown by equation (5) cannot be obtained. Yes, capacitors 01-C4 in parallel with resistors R2-R5
The purpose of this is to shorten the response time of the transistors Q, to Q4 and make the change in waveform steep.

In addition, in FIG. 1, the causes of measurement errors are: 11L1 Non-linear characteristic lb of the humidity sensing element, VTH variation due to gate circuit temperature 16,
The response delay time 1d of ptr, the fluctuation of the output voltage due to temperature of If/l, etc. can be eliminated by the following measures or reasons.

2&, correction is performed by processor processing or correction circuit.

In the 2bS2b5C- circuit, ΔvTH/Δθ = -3m
At V/'C, +0.06%F at 020-50℃
Since it is less than S, it can be ignored.

20. By setting the period T to a dog, it can be ignored.

In the case of the 2d, C-MO3 circuit, there is no particularly large variation and can be ignored.

Therefore, C-
If you use the MO8 circuit or equivalent and apply each condition of 2a, it is possible to have a sufficiently large period T, and the condition of 9.2e is also satisfied, achieving stable and highly accurate temperature measurement. do.

In addition, there is no need for an ADC, and by increasing the period T, there is no need for a frequency divider, etc., and the entire device is inexpensive, and the polling signal etc. can be used as the control signal So only during measurement. This reduces power consumption, temperature rise of each circuit element, self-heating of the humidity sensing element, etc., and improves measurement accuracy. Moisture sensing element C compared to lithium type humidity sensing element
I becomes cheaper.

FIG. 3 is a circuit diagram showing another embodiment; in this case, the first CPA includes resistors R11+R12, capacitor C111012 and transistor Q111Q12, resistor R13+R14, capacitor C13+C1
4 and a second CPA formed by transistors Qss + Q14 are connected in cascade, and inverters IN1 and IN2 are connected in parallel with each of them, and the transistor Q
Inserting a moisture sensitive element CH in series into the first feedback circuit between the in-phase output of the CPA by 111Q12 and the input of the NAND gate G via the resistor R1, while the anti-phase output of the CPA by the transistors Q13 + Q10. By inserting a thermistor TH and resistors R6+R7 in series into a second feedback circuit between the inputs of the NAND gate G and the input of a similar NAND gate G, the pulsed signal from the output OUT is The operation situation is the same as that shown in FIG.

However, the input threshold voltage of each CPA is the base-emitter voltage vBic of transistors Qll to Q14.
Well, this is about 1.4v, while C-
The input resistor voltage of the MO8 circuit is approximately 2.5V fi, and the response to the rise from "L" to "H#" is
Even though PAO is faster, inverters IN1 and IN2 respond faster to a fall from 'H' to -L, so for the purpose of making the multi-waveform change steeper by the faster response operation, Each CPA and inverters IN, IN2 are connected in parallel.

In addition, in FIG. 3, a CP with sufficient drive output is
Since A is connected in cascade, the operation is more stable than in FIG.

Note that as the humidity sensing element and the temperature sensing element, other equivalent elements may be used depending on the conditions (it is also possible to use a palm gate, inhibit gate, etc. in place of the NAND gate G, It is sufficient that each CPA generates outputs having phases opposite to each other, and various modifications can be made, such as by appropriately inserting an inverter or the like on the input side depending on the situation.

[Effects of the Invention] - From the above explanation, it is clear that according to the present invention, a pulse-like signal with a period corresponding to the humidity can be immediately obtained, and especially in AD.
C. It does not require a frequency divider, has a generally inexpensive structure, and can be operated only when necessary, reducing the temperature rise of each circuit element and the self-heating of the moisture-sensitive element. Since the humidity is reduced, the measurement situation is stable and accurate, and a remarkable effect can be obtained in various humidity measurements.

[Brief explanation of the drawing]

The figure shows an embodiment of the present invention, and FIG. 1 is a basic circuit diagram;
FIG. 2 is a diagram showing waveforms of various parts in FIG. 1, and FIG. 3 is a circuit diagram showing another embodiment. G...NAND gate (logical product circuit), IN. IN, , IN2...Inpark, Q1~Q4
, Cht~Q14...transistor, TH...
Thermistor (temperature sensing element), CI (...moisture sensing element, S
C...Control signal.

Claims (1)

[Claims] An AND circuit in which a feedback signal is given to one input and a control signal is given to the other input, and each of the AND circuits inverts and amplifies the output of the AND circuit, and has outputs that are in opposite phases to each other and each has a low output. first and second complementary push-pull amplifiers exhibiting an impedance; first and second feedback circuits each providing a feedback signal from each output of each amplifier to the one input; A humidity sensing element whose capacitance value changes depending on the humidity is inserted in series to one of the feedback circuits, and a humidity sensing element whose resistance value changes depending on the temperature is inserted in series to either one of the feedback circuits. A humidity measurement oscillation circuit characterized by comprising a temperature element.