JPH018025Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage pulse width converter that converts a voltage to be measured into a pulse width corresponding to the magnitude of the voltage. More specifically, the present invention relates to a voltage pulse width converter that eliminates the need for span adjustment in the input amplifier section.

2. Description of the Related Art Double-integration type analog-to-digital converters (hereinafter simply referred to as A/D converters) have been known. A double-integration type A/D converter integrates an input unknown voltage for a certain period of time, then integrates the reference voltage back and forth, and calculates the time width from the start of the loop-back integration until the output falls below a certain constant value (for example, zero potential). Utilizing the fact that it is proportional to the input unknown voltage, this time width is converted into a number of pulses, and this number of pulses is used as the output.

FIG. 1 is an electrical connection diagram showing a conventional example of a voltage pulse width converter used in a double integral type A/D converter. As described above, the voltage pulse width converter converts the voltage to be measured into a pulse width corresponding to the magnitude of the voltage. In the same figure, resistance R ₁ ,
A circuit composed of an operational amplifier U ₁ and a variable resistor R _V constitutes an input amplifier. The input amplifier is also called a preamplifier and converts the voltage to be measured V _io to an appropriate level. Resistance R ₂ , R ₃ , Resistance R ₃
The reference voltage E _S connected to one end of the switch SW ₁ ,
A circuit including SW ₂ , operational amplifier U ₂ , capacitor C, and switch SW ₃ connected to both ends of capacitor C constitutes an integrator. The integrator switches the input amplifier output V ₁ and the reference voltage E _S SW ₁ ,
Switch with SW ₂ and integrate.

U ₃ is a comparator that compares the output V ₂ of the integrator with zero potential. The output V _OUT of comparator U ₂ becomes the output of the circuit shown in FIG. A control section (not shown) controls each switch in the circuit shown in the figure. For example, a microcomputer is used as the control section. The operation of the circuit configured as described above is summarized as follows.

The input unknown voltage V _io is converted to an appropriately large level V ₁ by an input amplifier. This voltage V ₁ is integrated for a fixed period T in a subsequent integrator. At this time, the switch states are SW ₁ on, SW ₂ and SW ₃ off. FIG. 2 is a diagram showing the output waveform of the integrator. While V ₁ is being integrated, the output waveform gradually rises as shown in the figure. After integrating the input voltage V ₁ for a period T, the reference voltage E _S is then integrated back. The state of the switch at this time is
SW ₂ is on, SW ₁ and SW ₃ are off. At the moment when the integrator output V ₂ crosses the zero level, the output of the comparator U ₃
V _OUT falls. Then switch _SW3 is turned on and the integrator is reset. Here, the reference voltage
The time during which E _S is integrated corresponds to the magnitude of the input voltage V _io . Therefore, by extracting this time width from the comparator _U3 , the circuit shown in FIG. 1 can be used as a voltage pulse width converter.

₁ in Figure 2 indicates the case where the input voltage is larger than ₂ . The time from the start of the fold-back integration until it crosses the zero level is the time T _W1 with respect to ₁ is ₂
time T _W2 is greater than W2. In the conventional circuit as described above, when the value of the span adjustment variable resistor R _V of the input amplifier fluctuates due to temperature change or the like, the value of the output value V ₁ changes, resulting in a measurement error. Furthermore, using a variable resistor increases the number of man-hours required for adjustment.

The present invention was devised in view of these points, and in addition to the reference voltage E _S , a second reference voltage E _R is provided at the entrance of the input amplifier, and the voltage is adjusted according to the integration result of this reference voltage E _R. A voltage pulse width converter is realized in which the integration time T of the input voltage V _io is varied, thereby eliminating the need for a variable resistor for adjusting the span of the input amplifier. Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 3 is an electrical connection diagram showing an embodiment of the present invention. Components that are the same as those shown in FIG. 1 are designated by the same numbers. The differences from the conventional example shown in FIG. 1 are as follows. First, a second reference voltage E _R is provided at the front stage of the input amplifier. The input unknown voltage V _io and the reference voltage E _R are each switched
Connected to the input amplifier via SW ₄ and SW ₅ . Further, as the feedback resistor of the amplifier _U1 , a resistor _R4 is used instead of the variable resistor _RV . The operation of the circuit configured in this way will be explained below.

First, consider the case where the input voltage V _io is integrated. At this time, switch SW ₄ is on and switch SW ₅ is off. The following equation holds true for one integration cycle.

V ₁ /R ₂ T=E _S /R ₃ T _W (1) Here, the symbols indicating each resistance were used as they were as the resistance values. V ₁ is the input voltage V _io converted to an appropriate value by an input amplifier. T is the integration time described above. T _W is the output pulse width of comparator U ₃ . Next, consider the case where the second reference voltage _ER is integrated. At this time, SW ₅ is turned on and SW ₄ is turned off. The following equation holds true for one integration cycle.

V _R /R ₂ T=E _S /R ₃ T _WR (2) Here, V _R is the reference voltage E _R converted to an appropriate value by the input amplifier. _TWR is the output pulse width of comparator _U3 .

Now suppose that the resistance of the input amplifier changes. The output of the amplifier changes from V _R to (V _R ±ΔV _R ). The following equation holds true for one integral cycle of voltage (V _R ±ΔV _R ).

(V _R ±ΔV _R )/R ₂ T=E _S /R ₃ (T _WR ±ΔT _R )(3) Here, ΔT _R is
This is the change in the output pulse width of _U3 . Also, the input unknown voltage naturally changes and becomes as shown in the following equation.

(V ₁ ±ΔV ₁ )/R ₂ T=E _S /R ₃ (T _W ±ΔT _W ) (4) Here, ΔV ₁ and ΔT _W are respective changes.

Now, in equation (3), the change in output pulse width ΔT _R =
If the integration time T is changed by ΔT so that it becomes 0, the following equation holds true.

(V _R ±ΔV _R )/R ₂ (T±ΔT) = E _S /R ₃ T _WR (5) Since the control circuit (not shown) can know T _WR and ΔT _R in equation (3), , ΔT can be calculated by proportional calculation. When (V ₁ ±ΔV ₁ ) is integrated by (T±ΔT), the following equation holds true for one integration cycle.

(V ₁ ±ΔV ₁ )/R ₂ (T±ΔT) = V ₁ ±ΔV ₁ /V _R ±ΔV _R・E _S /R ₃ T _WR (6) On the other hand, V ₁ ±ΔV ₁ /V _R ±ΔV _R =V ₁ (1±ΔV ₁ /V ₁ )/V _R (1±
ΔVR/VR) (7) When formula (7) is substituted into formula (6), formula (6) becomes the following formula.

(V ₁ ±ΔV ₁ )/R ₂ (T±ΔT) = E _S /R ₃ T _W (8) Equation (8) shows that the input voltage of the integrator varies from V ₁ to (V ₁ ±
ΔV ₁ ), the output pulse width remains V ₁
It becomes T _W corresponding to . Therefore, accurate pulse width can be output.

FIG. 4 is a diagram showing the output waveform of the integrator.
In the figure, ₃ is the output waveform under normal conditions. ₄ , the input voltage of the integrator varies from V ₁ to (V ₁ ±
This is the output waveform when the voltage changes to ΔV ₁ ). ₅ is
This is the output waveform when the integration time is corrected by ΔT. The output pulse width of the comparator is the same as in case ₃ . In the above description, the case where the resistance of the input amplifier changes has been explained, but the same applies to the case where the resistance of the integrator changes. According to the present invention, since the input integration time is corrected by hardware, high-speed voltage pulse width conversion can be performed. Note that it is not necessary to correct the integration time T for each integration cycle. For example, the rate may be 1 in 10 conversion cycles. Further, the positive input terminal of the operational amplifier _U1 may not be grounded, but may be applied with a bias voltage. Since the integral type voltage pulse width converter shown in the figure becomes unstable when the input is near 0, a bias voltage is often applied to it.

As explained in detail above, according to the present invention, even if the resistance of the input amplifier changes, it is possible to compensate for the change, thereby realizing a voltage pulse width converter that eliminates the need for a variable resistor for adjusting the span of the input amplifier. be able to.

[Brief explanation of the drawing]

FIG. 1 is an electrical connection diagram showing a conventional example of a voltage pulse width converter, and FIG. 2 is a diagram showing an output waveform of an integrator. FIG. 3 is an electrical connection diagram showing an embodiment of the present invention, and FIG. 4 is a diagram showing an output waveform of an integrator. R ₁ to R ₄ ...Resistance, R _V ... Variable resistance, U ₁ , U ₂
...Operation amplifier, U ₃ ...Comparator, SW ₁ to SW ₄
...Switch, E _S , E _R ...Reference voltage.

Claims (1)

[Scope of claim for utility model registration] Input voltage for a certain time T (referred to as input integral time T)
, and then integrates the first reference voltage E _s in the opposite direction, making the input voltage equal to the integration time of the first reference voltage.
In a voltage pulse width converter that includes an integrator that converts into T _w (referred to as conversion integration time T _w ) and a comparator that receives the output of this integrator and generates a pulse width corresponding to the input voltage, an amplifier circuit that selects and amplifies either the measured voltage or the second reference voltage E _R ; and a switch means that switches between the output of the amplifier circuit and the first reference voltage E _S and applies it to the integrator. , the amplifier circuit changes the input integration time T by controlling the switch means based on the conversion integration time T _W1 when the output of the amplifier circuit is applied to the integrator when the second reference voltage E _R is selected. A voltage pulse width converter comprising: a controller for correcting gain fluctuations of an integrator; and a voltage pulse width converter.