JPH0533062Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention generally relates to a variable output power source, and more particularly to a voltage supply device whose output impedance always exhibits a constant resistance value over a wide frequency band.

[Technical background of the invention and its problems]

Conventionally, for example, when an open-ended transmission line (characteristic impedance Z ₀ ) is driven by a voltage supply device, an element with impedance Z ₀ is inserted between the device and the transmission line to achieve impedance matching. However, the output impedance of a voltage supply device has frequency characteristics, and its value usually becomes large in the high frequency region. Ringing due to reflection was superimposed on the waves. This ringing has a serious effect when the load (having a large input impedance) connected to the end of the transmission line requires high precision with respect to the level of the square wave.

In order to solve this problem, a circuit shown in FIG. 4 was devised. In the figure, the output of an operational amplifier 401 for voltage supply is grounded via a capacitor C ₀ . Therefore, the high frequency region output impedance at this point decreases. However, this circuit requires the capacitor C ₀ to have a large capacity and good high frequency characteristics, which becomes an obstacle to miniaturization of the circuit and increases cost. Furthermore, electrolytic capacitors are often used as large-capacity capacitors, making handling difficult when non-polarization is required. Further, in order to prevent oscillation due to the capacitor load, when phase compensation is applied to the operational amplifier 401, the output impedance becomes high in the frequency region between the low frequency region where the operational amplifier acts and the high frequency region where the capacitor acts.

[Purpose of invention]

An object of the present invention is to provide a voltage supply device whose output impedance exhibits constant resistance characteristics over a wide frequency band.

[Summary of the idea]

According to an embodiment of the present invention, a composite amplifier having an output impedance _Z1 , a first resistor having a resistance value R, one end of which is connected to the output of the composite amplifier, and the other end of the first resistor connected to the output of the composite amplifier. A second resistor with a resistance value R and an impedance connected at one end and grounded at the other end
A voltage supply device is provided that includes a one-port series connection circuit with an impedance element of Z ₂ and outputs a supply voltage from a connection point between the first resistor and the second resistor.

By selecting and designing each element so that the output impedance of the voltage supply device satisfies R ² ≒ Z ₁・Z ₂ , the output impedance is a constant resistance with a resistance value R that is almost constant over a wide frequency band. have characteristics.

Further, the composite amplifier includes a first amplifier having one input as a signal for setting the supply voltage value, and an output whose input is connected to the output of the first amplifier and whose output is the output of the composite amplifier. a second amplifier with impedance R ₀ ; a third resistor with a resistance value R ₁ connected between the output of the second amplifier and the other input terminal of the first amplifier; and the first amplifier a capacitance value C ₁ connected between the output of the amplifier and the other input terminal of the first amplifier.
In the case of a _{configuration} including ^a _{capacitor of} ² = R ₀ (C ₁ R ₁ +1/ω _T ), each element is selected so that R<<R ₀ is satisfied.

[Example of idea]

FIG. 1 shows a voltage supply device 10 according to an embodiment of the present invention.
Indicates 0. A signal for setting the output supply voltage to a predetermined voltage value is input to the non-inverting input terminal of the operational amplifier 101. The output of the operational amplifier 101 is connected on the one hand to the input of the current booster 102, and on the other hand to the inverting input terminal of the operational amplifier 101 via the phase compensation capacitor _C1 . On the other hand, the output of the current booster 102 is connected to a resistor for phase compensation.
_R1 is connected to the inverting input terminal of the operational amplifier 101, and the other end is connected to one end of a one-port circuit consisting of a series connection of a resistor 106 and a capacitor C, the other end of which is grounded. . resistance 1
The junction between 05 and resistor 106 provides the supply voltage output.

Here, the output impedance at point P in the same figure is
If jω・CR ² is set, the voltage supply device 10
The output impedance Z of 0 is calculated using the circuit shown in Figure 2, and is 1/Z=1/1/jωC+R+1/jωCR ² +R
=jωC/1+jωCR+1/jωCR ² +R =jωC+1/R/1+jωCR=1/R(
1+jωCR)1+jωCR=1/R ∴Z=R It can be seen that the resistance value is constant regardless of the frequency.

Furthermore, in order to set the output impedance at point P to jωCR ² , each element may be selected so as to satisfy CR ² =R ₀ (C ₁ R ₁ +1/ωr) and R<<R ₀ .

This is derived as follows using FIG.
Here, the transfer characteristic of the operational amplifier 101 is assumed to be a monopole characteristic with an amplification factor of 1 at ω _T , and the output impedance of the current booster 102 is assumed to be R ₀ .

From the figure, Z ₁ = V ₀ /I ₁ +I ₂ V ₀ −V ₁ = I ₁ R ₀ V ₁ = −V ₂・ω _T /jω V ₀ −V ₂ = I ₂ R ₁ V ₂ −V ₁ = I ₃・1/jωC _1Here , I ₃ ≒I ₂ , L ₁ >>I ₂ , so Z ₁ = R ₀ /1+1/jωC ₁ R ₁ +jω/ω _T (1+jωC ₁
R ₁ )ω<<1/C ₁ R ₁ +1/ω _T ... Z ₁ ≒jωR ₀ (C ₁ R ₁ +1/ω _T )... Also, since we want Z ₁ to be jωCR ² , the formula From ∴ CR ² = R ₀ (C ₁ R ₁ +1/ω _T )...Furthermore, the above approximation does not hold until the frequency ω = 1/CR where the actions of amplifiers 101 and 102 and the action of capacitor C cross over. Because I can't,
Using formula and formula, 1/C ₁ R ₁ + 1/ω _T >> 1/CR=R/R ₀・1/C ₁ R
₁ +1/ω _T ∴ R<<R ₀ ... Therefore, if the formulas and formulas are satisfied, the output impedance Z ₁ can be set to jωCR ² .

Note that the configuration of phase compensation is not limited to the configuration shown in Figure 1;
Any configuration may be used as long as Z ₁ is set to a predetermined value. Further, the positions of the resistor 106 and the capacitor C may be upside down.

As a result, the capacitor C ₀ (Figure 4) used to be a non-polar capacitor composed of two 10μF capacitors, but now only one 0.33μF ceramic capacitor is required, resulting in a smaller circuit. At the same time, costs decreased and high frequency characteristics improved. Furthermore, this circuit can be integrated into a hybrid IC (HIC).
In the past, an electrolytic capacitor had to be attached externally, so the amplifier 401 shown in FIG.
Since the output terminal of the HIC goes outside through the terminal of the HIC, there is a risk of damage due to careless shooting.
For this reason, it was necessary to provide a current limiting circuit, but
In one embodiment of the present invention, the capacitor is built into the HIC, so such a current limiting circuit is not required. In addition, in the circuit shown in FIG. 4, when the reference voltage was changed, the surge current caused by the large capacitance capacitor C ₀ caused various problems, but such problems have been eliminated.

Further, the voltage supply device according to the embodiment is used in a circuit as shown in FIG. 5, where a bias voltage is applied to one end of the load resistor R _L , and R _L is selected to be equal to the characteristic impedance Z ₀ of the transmission line. In this case, it is also possible to provide good termination characteristics for the transmission line.

[Effect of idea]

As explained above, by using the present invention, it is possible to perform good signal transmission and reception without the influence of reflection due to impedance mismatch.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a voltage supply device according to an embodiment of the present invention, FIG. 2 is a diagram used to calculate the output impedance of the device in FIG. 1, and FIG. 3 is a diagram showing the two amplifiers in FIG. 1. FIG. 4 is a diagram showing a conventional voltage supply device, and FIG. 5 is a diagram showing an application of an embodiment of the present invention. 101...Operation amplifier, 102...Current booster, R, _R1 ...Resistor, C, _C1 ...Capacitor.

Claims (1)

[Claims for Utility Model Registration] (1) An amplifier having an output impedance _Z1 , a first resistor having a resistance value R, one end of which is connected to the output of the amplifier, and the other end of the first resistor. A second resistor means having a resistance value of approximately R and an impedance value connected to
^a series connection circuit with _an impedance means _of Z ₂ ; A voltage supply device characterized by outputting. (2) The amplifier includes: a first amplifier; a capacitor having a capacitance value C ₁ connected between the output terminal and the inverting input terminal of the first amplifier; and a capacitor connected to the output terminal of the first amplifier; and a resistor having a resistance value R ₁ connected between the output terminal of the second amplifier and the inverting input terminal of the first amplifier, and the impedance means is a capacitance. The voltage supply device according to claim 1, which is a registered utility model, characterized in that when the capacitor has a value C, the following relational expression holds between the values. Relational expression: CR ² ≒ R ₀ (C ₁ R ₁ +1/ω _T ) Here, R ₀ (R ₀ ≫R) is the output impedance of the second amplifier, and ω _T is the gain transfer of the first amplifier. This is the angular frequency when the gain in the characteristic becomes 1.