JPH07243862A - Sensor drive circuit - Google Patents

Abstract

PURPOSE:To provide a sensor circuit which has a high compensation accuracy, can arbitrarily set a sensor drive voltage, and has a temperature compensation function which can be widely applied for arbitrary temperature characteristics of a sensor. CONSTITUTION:A constant voltage Vr which does not depend on a sensor temperature (t) of a first voltage generation circuit 4 and a voltage Vt corresponding to a sensor temperature (t) of a second voltage generation circuit 5 are input to a drive voltage generation circuit 10 consisting of a first multiplication circuit 6 for obtaining betaVr (beta: constant), a second multiplication circuit 7 for obtaining gammaVr (gamma: constant), a subtraction circuit 8 for obtaining betaVr-gammaVt to generate a sensor drive voltage Vs. A relation of gammaVt=betaVrXa(t-t0) [a: the temperature coefficient of sensor output which the sensor itself has, t0: a reference temperature] is established between gammaVt and betaVr. The drive voltage generation circuit 10 can also be configured as shown in Fig.B using an operation amplifier 13 and a plurality of resistors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor drive circuit for compensating the sensitivity temperature dependence of a constant voltage drive type sensor, and is not particularly limited by the sign or size of the temperature coefficient of the sensor output voltage, and has a wide range of applications. It relates to a circuit having a range.

[0002]

2. Description of the Related Art Conventionally, for example, a sensor for detecting current or direction using a Hall element, other pressure sensor, acceleration sensor, etc. have been driven by a constant current or a constant voltage. The constant voltage drive has been widely used because of its circuit accuracy and ease of adjustment. These sensors generally have a temperature coefficient in their sensitivity. In this case, as the temperature compensation method, (1) a method of driving with a constant voltage and compensating with an amplifier circuit in the subsequent stage.

(2) A method of compensating the driving voltage by giving it a temperature coefficient that cancels the temperature fluctuation of the sensor. It can be performed by two methods. However, the method (1) is mainly performed by the method (2) because the change in temperature is compensated as the change in the amplification degree, and it is difficult to maintain accuracy and stability. Therefore, the method (2) will be described in detail.

Generally, the output V _o of the sensor is proportional to the sensor driving voltage V _s and can be approximated as a linear function of the temperature T. That is, V ₀ = eV _s (1 + aT) (1) where e is a proportional constant and a is a temperature coefficient of the output voltage of the sensor itself. Therefore, the sensor drive voltage V _s is -a
When given as a function of the input voltage (power supply voltage) V _i , V _s = V _i (1-aT) (2) Substituting the formula (2) into the formula (1), V _O = eV _i (1-aT) (1 + aT) (3) = eV _i (1-a ² T ² ) ... (4) Here, a << 1, and usually 1 >> a ² T ² holds, so V _Since o≈eV _i (5), the sensor output voltage V _o is hardly affected by temperature.

A conventionally known method is as shown in FIG.
Sensor drive voltage V with temperature coefficient _sTo get
Force voltage V_iThe base of silicon transistor Q
Voltage V_BEVoltage V amplified_CEIt ’s what you get by subtracting
is there. V_s= V_i-V_CE (6) Since the base current of the transistor Q is very small, V_CE= V_BE(1 + R₂/ R₁) (7) Substituting equation (7) into equation (6), V_s= V_i-V_BE(1 + R₂/ R₁) (8) Substituting equation (8) into equation (1) V_o= E {V_i-V_BE(1 + R₁/ R₂)} (1 + aT) (9) V_BEIs a linear function of temperature_BE= BT + c (10) By substituting the equation (10) into the equation (9) and transforming it, V₀= E {V_i-C (1 + R₁/ R₂) -BT (1 + R₁/ R₂)} (1 + aT) = e {V_i-C (1 + R₁/ R₂)} [1- (1 + R₁/ R₂) BT / {V_i-C (1 + R₁/ R₂)}] (1 + aT) (11) where (1 + R₁/ R₂) B / {V_i-C (1 + R₁R₂)} = A (12) R₁/ R₂= {A / (ac + b)} V_iR such that -1 (12 ') holds₁/ R₂If you set V_o= E {V_i-C (1 + R₁/ R₂)} (1-a²T²) (13) a << 1 and usually 1 >> a²T²Is satisfied, so V_o≒ e {V_i-C (1 + R₁/ R₂)} (14) and the sensor output voltage V_oCan reduce the effect of temperature
It

[0006]

The conventional method shown in FIG. 3 has the following problems. Dispersion of c when V _BE is represented by bT + c When the distribution of c in Eq. (14) varies, the sensitivity of the output V _o also varies. Variation in temperature coefficient b of V _BE R ₁ / R ₂ is determined by the equation (12 ′), but since b varies, the equation (12 ′) can be established only by a rough approximation. Therefore, the equation (14) V _o is accompanied by an error due to variations in the temperature coefficient b.

Change in Sensor Driving Voltage Compared with V _o ≈eV _{i in} formula (5), formula (14) has a term including c, and V _{i in} formula (5) deviates. c (1+
The R ₁ / R ₂ ) term is dependent on R ₁ / R ₂ and therefore the input voltage V _i and thus the sensor drive voltage V _s cannot be independently determined. Limit of temperature coefficient that can be compensated From the expression (12), when {a / (ac + b)} V _i <1, the right side becomes negative, and R ₁ / R ₂ which satisfies the expression (12 ′) is satisfied.
The value of does not exist and the temperature cannot be compensated.

If the temperature coefficient a> 0 of the sensor cannot be compensated. Since the temperature coefficient b of V _BE has a negative value, it is not possible to compensate a sensor having a positive temperature coefficient a, as can be seen from the equation (12). The method of compensating the driving voltage V _s by giving it a temperature coefficient is as follows.
, The compensation accuracy is deteriorated due to the variation in the temperature characteristics of the V _BE of the transistor as in the item, and the sensor drive voltage V _s cannot be arbitrarily set as in the item.
As in the item above, if the temperature coefficient a of the sensor is positive, it cannot be compensated, and in some cases, even if a is negative, it cannot be compensated. For example, the applicable range of this compensation method is narrow. There is a drawback of.

The object of the present invention is to solve these conventional drawbacks, to provide a high compensation accuracy, to set the sensor drive voltage arbitrarily, and to apply it to a wide range of temperature characteristics of the sensor. It is intended to provide a drive circuit having

[0010]

[Means for Solving the Problems]

(1) The sensor drive circuit according to claim 1 includes a first voltage generation circuit that generates a constant voltage V _r that does not depend on the sensor temperature t,
A second voltage generating circuit for generating a voltage V _t corresponding to the sensor temperature t; a first multiplying circuit for multiplying an output voltage V _r of the first voltage generating circuit by a predetermined first constant β; subtracting the second multiplication circuit for multiplying a predetermined second constant γ in the output voltage V _t of the voltage generating circuit, the output .gamma.V _t of the second multiplier circuit from the output .beta.v _r of the first multiplier circuit, the difference Value β
And a subtraction circuit that outputs V _r −γV _t as a sensor drive voltage.

Then, between the output βV _r of the first multiplication circuit and the output γV _t of the second multiplication circuit, γV _t = βV _r × a (t−t ₀ ) a: the sensor output of the sensor itself. Temperature coefficient t ₀ : reference temperature is given.

(2) According to another aspect of the sensor drive circuit of the present invention, a first voltage generating circuit for generating a constant voltage V _r independent of the sensor temperature t, and a predetermined constant β for the output V _r of the first voltage generating circuit. And the output βV _r of the first multiplier circuit is multiplied by a (t−t ₀ ), where a is the temperature coefficient of the sensor output of the sensor itself, and t ₀ is the reference temperature. The output βV _{r of} the second voltage generation circuit and the first multiplication circuit
From the output of the second voltage generating circuit βV _r × a (t-
t ₀₎ is subtracted and a subtraction circuit for outputting the difference value as the sensor driving voltage, the constructed.

(3) According to another aspect of the sensor drive circuit of the present invention, a first voltage generation circuit for generating a constant voltage V _r independent of the sensor temperature t and a second voltage for generating a voltage V _t corresponding to the sensor temperature t. Inputting the generator circuit and the outputs V _r and V _t of the first and second voltage generator circuits, respectively, γV _t = βV _r × a (t−t ₀ ) a: temperature coefficient of the sensor output of the sensor itself t ₀ : reference temperature; β, γ: a constant value, a driving voltage generating circuit composed of an operational amplifier and a plurality of resistors for calculating βV _r −γV _t and outputting the calculated value as a sensor driving voltage. , Composed of.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is based on the sensor drive voltage V_sOf (2)
Like V_s= V_i{1-α (t₀-T)} = V_i{1 + α (t-t₀)} (15), the temperature coefficient of the sensor is compensated and driven.
Voltage V_sCan be independently determined. Where t
₀Is the reference temperature, t is the sensor temperature, and α is the drive voltage V. _sThe temperature of
It is a frequency coefficient. Equation (15) is V_s= V_i-V_iα (t₀-T) can be transformed into (16), where βV_r= V_i … (17) γV_t= V_iα (t₀-T) (18) voltage V which does not depend on temperature_rAnd its coefficient β and temperature
Voltage V as a function_tAnd its coefficient γ_s= ΒV_r-ΓV_t It can be expressed as (19).

ΒV_rAnd γV_tThe relationship with (17), (1
From equation 8), βV_r= ΓV_t/ Α (t₀-T) ∴γV_t= ΒV_r× α (t₀-T) (20) The sensor drive circuit 1 according to the present invention is operated at a temperature as shown in FIG.
Independent constant voltage V _rVoltage generation circuit 4 for generating
And the voltage V as a function of temperature_tSecond voltage generation to generate
Circuit 5 and V_r, V_tCalculation times for multiplying by β and γ respectively
Roads 6, 7 and βV_rIs γV_tA subtraction circuit 8 for subtracting
Output voltage V of the subtraction circuit 8_s= ΒV_r-ΓV_tOutput
It is composed of a voltage follower circuit 9. But the voltage follower
A circuit may be omitted. First and second multiplication circuits 6,
7, driving by subtractor circuit 10 and voltage follower circuit 9
The pressure generation circuit 10 is configured.

Now, consider temperature compensation when the sensor output V _o has a temperature coefficient peculiar to the sensor and is given by the equation (1). (2) in comparison equation (15), -a = α ... (21) T = t-t 0 ... (22) (18) Equation (21) Substituting equation γ = aV _i / { V _t / (t−t ₀ )} (18 ′) Substituting the expression (21) into the expression (20), γV _t = βV _r × a (t−t ₀ ) (20 ′) FIG. 1B is a diagram. 7 is another example of the configuration of the drive voltage generating circuit 12 of 1A. Set the voltage at the two input terminals of the operational amplifier 13 to V ₊ V
_- and if _{V + = V r × R 5} / (R 4 + R 5) ... (23) currents I _1, I _2, defines a I ₃ as shown in FIG. In put, Figure 1B
At the point P of, I ₁ + I ₂ = I ₃ holds. Therefore, (V _t −V ₋ ) / R ₃ + (V _s −V ₋ ) / R ₂ = V ₋ / R ₁ (24) Equation (23) is modified to R ₁ R ₂ (V _t − _{V -) + R 1 R 3} (V S -V -) -R 2 R 3 V - = 0 ... (25) ∴V - = (R 1 R 2 V t + R 1 R 3 V S) / (R 2 R ₁ + R ₃ R ₁ + R ₂ R ₃ ) (26) Since V ₊ = V ₋ in the ideal amplifier, (22), (2
5) than _{V s = {R 5 (R} 1 R 3 + R 1 R 2 + R 2 R 3) / R 1 R 3 (R 4 + R 5)} V r - (R 2 / R 3) V t ... ( 27) When equation (26) is associated with equation (19), β = R ₅ (R ₁ R ₃ + R ₁ R ₂ + R ₂ R ₃ ) / R ₁ R ₃ (R ₄ + R ₅ ) ... (28) γ = R ₂ / R ₃ (29) By substituting the expression (29) into the expression (18 ′), γ = R ₂ / R ₃ = aV _i (t−t ₀ ) / V _t (30) = aV _i / {V _t / (t−t ₀ )} (30 ′) It is sufficient to select R ₂ and R ₃ that satisfy the equation (30 ′).

As an example, a = 1000 ppm / ° C.,
As the expression (17) is satisfied, βV _r = V _i = 5 V; β = 1 ... (31) is given. When V _t / (t−t ₀ ) = 1 mV / ° C. (32), (18) ′) And (30 ′) are satisfied γ = R ₂ / R ₃ = aV _i / {V _t / (t−t ₀ )} (33a) = 1000 × 10 ⁻⁶ × 5 / { 1 × 10 ⁻³ } (33b) = 5 is set. For that purpose, for example, R ₂ = 50 kΩ, R
₃ = 10 kΩ may be set.

By transforming the equation (27), β = {R ₅ / (R ₄ + R ₅ )} (1 + R ₂ / R ₃ + R ₂ / R ₁ ) ... (34) In the above example, β = 1 and β = 1 = {R ₅ / (R ₄ + R ₅ )} (1 + 5 + R ₂ / R ₁ ), for example, R ₄ = 50k, R ₅ = 10k, R ₁ = ∞
And it is sufficient.

In the case of this example, equations (17) and (1
8 ′) is satisfied so that βV _r and γV _t are set to (3
Since it is given by the equations (1) and (33), naturally (2
The expression 0 ') is established. By the way, (3
3) Substituting equation (31) into _{equation, γV t = aV i (t} -t 0) = βV r a (t-t 0) ... (20 ') , and the (20') below is obtained immediately .

The voltage V _r that does not depend on temperature can be easily generated by using a reference diode or a Zener diode, and the voltage V _{t that} is a function of temperature can be easily generated by using an IC temperature sensor, a platinum thin film resistor or a thermistor. .

[0021]

According to the present invention, the first voltage generating circuit 4 for generating the voltage V _r independent of the sensor temperature t, and the second voltage generating circuit 5 for generating the voltage V _t dependent on the sensor temperature t. , Drive voltage V _s = βV _r −γV _t = βV _r {1-
a (t−t ₀ )} [But γV _t = βV _r × a (t−
t ₀ ); a is a temperature coefficient of the sensor itself, β and γ are constants], and the driving voltage generating circuit 10 and the sensor driving circuit are combined. Moisture, highly accurate temperature compensation, and βV
By appropriately setting _{r, it} is possible to generate a sensor drive voltage V _S of any magnitude.

[Brief description of drawings]

1 is a block diagram showing an embodiment of the invention of claim 1, and B is a circuit diagram showing a modified example of the drive voltage generating circuit 10 of FIG.

FIG. 2 is a block diagram showing an embodiment of the invention of claim 2;

FIG. 3 is a circuit diagram showing an example of a conventional sensor drive circuit.

Claims (3)

[Claims] 1. A constant voltage V _r independent of the sensor temperature t.
A first voltage generating circuit for generating a second voltage generating circuit for generating a voltage V _t corresponding to the sensor temperature t, the β first constant predetermined output voltage V _r of said first voltage generating circuit multiplication A second multiplication circuit for multiplying the output voltage V _t of the second voltage generation circuit by a predetermined second constant γ; and an output β V _r of the first multiplication circuit to the second multiplication circuit. the output .gamma.V _t subtracts the, comprising a subtraction circuit which outputs the difference value βV _r -γV _t as sensor driving voltage and output .gamma.V _t output .beta.v _r and the second multiplier circuit of the first multiplier circuit The sensor drive circuit is characterized in that a relation of γV _t = βV _r × a (t−t ₀ ) a: temperature coefficient of sensor output of the sensor itself t ₀ : reference temperature is given between 2. A constant voltage V _r independent of the sensor temperature t.
A first voltage generating circuit for generating a voltage, a first multiplier circuit for multiplying the output V _r of the first voltage generating circuit by a predetermined constant β, and an output βV _r of the first multiplier circuit for a (t−t ₀ ) (Where a is the temperature coefficient of the sensor output of the sensor itself, t ₀ is the reference temperature), and a second voltage generating circuit for generating a voltage, and the second voltage from the output βV _r of the first multiplying circuit. A sensor drive circuit comprising: a subtraction circuit that subtracts the output βV _r × a (t−t ₀ ) of the generation circuit and outputs the difference value as a sensor drive voltage. 3. A constant voltage V _r independent of the sensor temperature t.
A first voltage generating circuit for generating a voltage, a second voltage generating circuit for generating a voltage V _t corresponding to the sensor temperature t, and outputs V _r and V _t of the first and second voltage generating circuits, respectively. , ΓV _t = βV _r × a (t−t ₀ ) a: temperature coefficient of sensor output of the sensor itself t ₀ : reference temperature; β, γ: when constants, βV _r −γV _t is calculated, and A sensor driving circuit comprising: a driving voltage generating circuit including an operational amplifier and a plurality of resistors, which outputs a calculated value as a sensor driving voltage.