JPH06120831A - Control voltage generating circuit - Google Patents

Abstract

PURPOSE:To acquire the marks of the control voltage equivalent to those acquired by an (n+1)-bit D/A converter by means of an n-bit D/A converter by performing the switching between the addition and the subtraction of the output of the D/A converter to and from the reference voltage by using a control signal. CONSTITUTION:A control voltage generating circuit consists of a digital input terminal 1, an n-bit D/A converter 2, a control voltage conversion circuit 3, a control voltage output terminal 4, an input data conversion circuit 5, and a polarity switching circuit 6. The circuit 6 switches the polarities according to 1 or 0 of the data Dn on the digital input. Then the output of the circuit 6 is added to the reference voltage VB by the circuit 3 and outputted to the terminal 4. The output of the circuit 3 acts on the minus side in 2<n> pieces centering on the voltage VB and also acts on the plus side in 2<n> pieces respectively. That is, 2<+1> pieces of control voltage can be generated and the effect equivalent to that secured by an (n+1)-bit converter is acquired.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control voltage generating circuit using a D / A converter.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a control voltage generating circuit using a conventional D / A converter. In FIG. 5, 1 is the digital input terminal of the D / A converter, 2 is the D / A converter that creates the basis of the control voltage, and 3
Is a control voltage conversion circuit for converting the output of the D / A converter 2 into a control voltage, and 4 is a control voltage output terminal.

Next, the operation of the conventional example will be described. First, the digital signal input to the digital input terminal 1 is converted into an analog amount by the D / A converter 2. This analog amount is converted into a voltage optimum for the controlled circuit by the control voltage conversion circuit 3 and output from the control voltage output terminal 4.

In this way, the digital signal input from the digital input terminal 1 is converted to create a control voltage.

[0005]

With such a conventional structure, when an n-bit D / A converter is used,
The number of points N at which the control signal exists is N = 2 ⁿ . Double the number of points where this control signal exists (2N)
To achieve this, it is necessary to use a (n + 1) -bit D / A converter.

As is well known, when an n-bit D / A converter is constructed, the relative accuracy required for the elements to be used is the relative accuracy of the elements ≦ 1/2 ^{n + 1} . Therefore, each time the effective number of bits of the D / A converter is increased by 1, the required accuracy of each element is increased by ½. In the semiconductor integrated circuit, in order to improve the accuracy of the element, it is necessary to increase the area of the element used or to improve the accuracy of the manufacturing process. In both cases, manufacturing costs are high. Further, depending on the manufacturing process, sufficient relative accuracy between the elements cannot be obtained, and there is a problem that manufacturing becomes impossible.

The present invention solves such a conventional problem by using an n-bit D / A converter and providing almost the same number of control points as when an (n + 1) -bit D / A converter is used. It is an object of the present invention to provide a control voltage generating circuit having the same.

[0008]

In order to achieve the above object, the present invention uses a D / A converter for converting digital input data into an analog quantity, and the input data of the D / A converter by another control signal. An input data conversion circuit that controls whether it is inverted or output as it is, a polarity switching circuit that switches the polarity of the output of the D / A converter with the control signal, and an output of the polarity switching circuit that is converted into a control voltage. It is a control voltage generation circuit including a control voltage conversion circuit.

[0009]

According to the present invention, the polarity of the output of the n-bit D / A converter is controlled by the control signal ((n + 1) th bit phase, etc.).
The control voltage is doubled by adding and subtracting the control voltage to the reference voltage, and the control voltage score is 2 ^{n + 1} as in the case of using the (n + 1) -bit D / A converter. Can be individual. Furthermore, by controlling whether the digital input to the D / A converter is inverted or passed as it is according to the control signal ((n + 1) th bit phase, etc.), n + 1 input data including the n input data and the control signal are added. Can be used in the same manner as in the case of using the (n + 1) -bit D / A converter.

As described above, the number of output points of the control voltage generating circuit can be doubled without improving the precision of the element used and the precision of the manufacturing process.

[0011]

1 is a block diagram showing an embodiment of a control voltage generating circuit according to the present invention. It comprises a digital input terminal 1, a D / A converter 2, a control voltage conversion circuit 3, a control voltage output terminal 4, an input data conversion circuit 5 and a polarity switching circuit 6. As described above, the signal input to the digital input terminal 1 is transmitted to the D / A converter 2
Is converted into an analog quantity. This analog amount is converted into a voltage optimum for the controlled circuit by the control voltage conversion circuit and output from the control voltage output terminal 4.

Next, the polarity switching circuit 6 connected to the output of the D / A converter 2 will be described. The output when the digital input to the n-bit D / A converter is i'is V (i '), and the output of the polarity switching circuit 6 is V
_S (i '), V _S (i') switches the polarity when the digital input data D _n is 1 or 0. That is, as an example, the following definition is made.

When D _n = 0 V _S (i ') =-V (i') When D _n = 1 V _S (i ') = + V (i') In this way, n-bit D / A The output of the converter is normally 2 ⁿ , but by switching the polarity with D _n , 2 · 2 ⁿ = 2 ^{n + 1} outputs are possible.

Output V _S (i ') of the polarity switching circuit 6
Is added to the reference voltage V _B by the control voltage conversion circuit 3 and output to the control voltage output terminal 4. The output V ₀ (i ′) is D _n = 0. V ₀ (i ′) = V _B + V _S (i ′) = V _B −V (i ′) D _n = 1 V ₀ (i ′) _{= V B + V S (i} ') = V B + V (i) , and the output about the reference voltage V _B of the control voltage conversion circuit, - ^the 2 ⁿ motion to the side, move ^the 2 ⁿ to + side, Ie 2
It is possible to generate ^{n + 1} control voltages, and the same effect can be obtained as when the D / A converter has (n + 1) bits.

In this case, the digital input (D ' ₀ , ... D' _n-1 ) to the D / A converter and the control voltage conversion circuit 3
FIG. 4 shows the relation with the output of In FIG. 4, when D _n is switched from “0” to “1”, the addition / subtraction state of the output V (i ′) of the D / A converter with respect to the reference voltage V _B is switched, as shown in FIG. The control voltage changes greatly.

It is the input data conversion circuit 5 that makes the characteristics of FIG. 4 change linearly. The inputs of the input data conversion circuit 5 are D ₀ , D ₁ ... D _n-1 , and the output is D' _0. , D' ₁ ...
... D' _n-1 is set, and it is converted whether it is inverted or through when D _n is "0" or "1". That is, in the case of D _n = 0, in the case of D ′ _i = D _i (i = 0, 1, ..., N−1) in the case of D _n = 1

[0017]

[Equation 1]

The digital inputs (D ₀ , D ₁ , ...
, D _n-1 ) and the output of the control voltage conversion circuit 3 are shown in FIG. As is apparent from FIG. 3, a control voltage proportional to the digital input can be created.

In this way, the data number of the output voltage is (n + 1) using the n-bit D / A converter.
A control voltage generation circuit having almost the same number of output points as a control voltage generation circuit using a bit D / A converter can be configured.

Further, since the output of the D / A converter is simply added / subtracted to / from the reference voltage, the change width of the control voltage is doubled, and the change amount per LSB is the same. Can be configured without enhancement.

FIG. 2 shows a more specific control voltage generating circuit according to an embodiment of the present invention. Inverter circuit I
NV _{0 to} INV _n-1 and AND circuit AND _{0,1 to} AND _n-1,2
And OR circuits OR _{0 to} OR _n-1 are specific examples of the input data conversion circuit. Digital input data D ₀
To D _n-1 are the same, the operation for data D ₀ will be described. D' _0, which is one of the outputs of the input data conversion circuit 5, is expressed in the following logical formula.

[0022]

[Equation 2]

Therefore, in the case of D _n = 0, as in the case of D' ₀ = D ₀ , the case of D _n = 1

[0024]

[Equation 3]

The operation is as described above. Next, the transistors Q _{1 to} Q ₈ and the resistors R _{1 to} R ₆ are specific examples of the polarity switching circuit 6, and the operation will be described. The transistors Q ₁ and Q ₂ are differential switches and switch the output of the D / A converter 2 with D _n . When D _n = 0, D /
The output current of the A converter 2 passes through the transistor of Q ₂ , passes through the current mirror circuit formed of the transistors Q ₅ and Q ₆ , passes through the current mirror circuit formed of the transistors Q ₇ and Q ₈ , and the resistor R ₇ Is converted into voltage by.
The control voltage output V _{0 in} this case is V ₀ = V _B −R ₇ · I _i , where I _i is the output current of the D / A converter, and is on the − side of the reference voltage V _B.

On the contrary, when D _n = 1, the output of the D / A converter 2 passes through the transistor of Q _{1 and} the current mirror circuit composed of the transistors Q ₃ and Q ₄ , and the resistance R Applied to ₇ . Therefore, V ₀ = V _B + R ₇ · I _i , which is on the + side of the reference voltage V _B. Thus, the relationship between the digital inputs (D ₀ , D ₁ , ..., D _n ) and the control voltage output is as shown in FIG.

[0027]

As is apparent from the above embodiment, the present invention uses the n-bit D / A converter to determine whether the output of the D / A converter is added to or subtracted from the reference voltage by the control signal ((n + 1 ) Bit phase, etc.) to switch (n +
1) It is possible to obtain the same control voltage score as that obtained by using a D / A converter of 1 bit.

Further, by converting the input data of the D / A converter by using the control signal ((n + 1) th bit phase or the like), it is possible to obtain (n
It can be regarded as equivalent to the case of using a +1) bit D / A converter.

[Brief description of drawings]

FIG. 1 is a block diagram of a control voltage generating circuit according to an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a more specific embodiment of the present invention.

FIG. 3 is a characteristic diagram of a digital input and an output control voltage of a control voltage generation circuit using the present invention.

FIG. 4 is a characteristic diagram of the output (D ′ ₀ , D ′ ₁ , ..., D ′ _n−1 ) of the input data conversion circuit of the control voltage generation circuit using the present invention and the output control voltage.

FIG. 5 is a configuration diagram of a conventional control voltage generation circuit.

[Explanation of symbols]

1 digital input terminal 2 D / A converter 3 controls the voltage conversion circuit 4 a control voltage output terminal 5 inputs data conversion circuit 6 polarity switching circuit Q ₁ to Q ₈ transistor R ₁ to R ₇ resistor INV ₀ INV _n inverter circuits the AND ₀₁ ~ AND _n-1,2 AND circuit OR _{0 to} OR _n-1 OR circuit V _B Reference voltage D _{0 to} D _n Digital input data D ′ _{0 to} D ′ _n Input data Output data of conversion circuit

Claims (1)

[Claims] 1. A D / A converter for converting digital input data into an analog quantity, and controlling whether the input data of the D / A converter is inverted or output as it is by controlling with another control signal. Control voltage generation including an input data conversion circuit, a polarity switching circuit that switches the polarity of the output of the D / A converter with the control signal, and a control voltage conversion circuit that converts the output of the polarity switching circuit into a control voltage circuit.