JPH0722901A - Attenuation circuit - Google Patents

Abstract

PURPOSE:To unnecessitate the adjustment of an attenuation circuit, to enable the operation from DC to a high frequency and to make operating temperature a wide range by composing the attenuation circuit by a first FET and a resistor and a second FET and a resistor and impressing a voltage by using a correction circuit for the gates of these FETs. CONSTITUTION:In an attenuation circuit 10, when Vc<Vmo is made by changing control voltage Vc, the voltage Vg of the output terminal 32o of a differential amplifier 32 or the gate voltage Vg of an FET 18 is reduced, the resistance value between the source 18s and the drain 18d of the FET 18 is increased, output voltage Vmo is increased and Vc=Vmo is made. Conversely, when Vc<Vmo is made by changing voltage Vc, the resistance value between the source 18s and the drain 18d is decreased by increasing voltage Vg and Vc=Vmo is made by decreasing voltage Vmo. Thus, voltage Vc and output voltage Vmo is made to be proportional, attenuators 16 and 22 are made to have the same characteristic and the same voltage Vg is impressed on the gates 12g and 18g of the FETs 12 and 18 by using a correction circuit 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an attenuation circuit used in communication, measurement and radio wave application fields.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing a conventional attenuation circuit. Hereinafter, description will be given with reference to FIG. The attenuation circuit 50 is a PI connected in parallel between the input side IN and the output side OUT.
Input side I of N diode 52 and PIN diode 52
A resistor 54 for voltage division connected in series with N and a function generator 56 for applying a control voltage Vc2 to the PIN diode 52.
And an inductance 58, capacitors 60, 6 necessary for applying the control voltage Vc2 to the PIN diode 52.
It is composed of 2, 64. Then, by changing the control voltage Vc2 applied to the PIN diode 52, the resistance value of the PIN diode 52 is controlled, and the input signal is divided by the PIN diode 52 and the resistor 54 to obtain a desired attenuation amount. ing. Further, since the voltage-resistance characteristic of the PIN diode 52 is non-linear, if the control voltage Vc1 is directly applied to the PIN diode 52,
As shown in FIG. 3, the relationship between the control voltage Vc1 and the attenuation amount A becomes non-linear. Therefore, by converting the control voltage Vc1 into the control voltage Vc2 by the function generator 56 to compensate the nonlinearity of the PIN diode 52, the control voltage Vc1
Attenuation amount proportional to is obtained.

[0003]

However, the conventional attenuation circuit 50 has the following problems. The function generator 56 is used to obtain the control voltage Vc2 that compensates for the non-linearity of the PIN diode 52, and this adjustment is complicated. Since the capacitors 62 and 64 for blocking direct current for applying the control voltage Vc2 to the PIN diode 52 are required, they do not operate in principle at low frequencies including direct current. Since the voltage-resistance characteristic of the PIN diode 52 changes with temperature, and the change directly affects the characteristics of the attenuation circuit, the operating temperature range is narrow.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an attenuation circuit which requires no adjustment, can operate from DC to high frequency, and has a wide operating temperature range.

[0005]

According to another aspect of the present invention, there is provided an attenuating circuit, wherein an input signal is divided between a source and a drain of a first field effect transistor and a first resistor to generate a voltage between the source and the drain. Is used as an output signal, and has the same characteristics as this attenuator, and the reference voltage is divided between the source and drain of the second field effect transistor and the second resistor to form the source and drain. A second attenuator having a voltage between them as an output voltage and a correction circuit for applying a voltage to the gates of the first and second field effect transistors so that the output voltage of the attenuator is proportional to the control voltage. Be prepared.

According to a second aspect of the present invention, in the attenuating circuit according to the first aspect, at least the first and second field effect transistors are formed on the same semiconductor chip.

[0007]

In the second attenuator, the reference voltage is divided between the source-drain of the second field effect transistor and the second resistor, and the source-drain voltage becomes the output voltage. When the control voltage is changed, the correction circuit changes the gate voltage of the second field effect transistor so that the output voltage is proportional to the control voltage. That is, the resistance value between the source and the drain of the second field effect transistor changes in proportion to the change in the control voltage. Further, the first and second attenuators have the same characteristics, and the same voltage is applied to the gates of the first and second field effect transistors by the correction circuit. Therefore, the resistance value between the source and drain of the first field effect transistor changes in proportion to the control voltage.

When the first and second field effect transistors are formed on the same semiconductor chip, the impurity concentrations of these field effect transistors are well matched.

[0009]

1 is a circuit diagram showing an embodiment of an attenuation circuit according to the present invention. A detailed description will be given below with reference to this drawing.

The attenuation circuit 10 includes a field effect transistor 1
The source signal 12s-drain 12d is formed by dividing the input signal Vin between the source 12s-drain 12d and the resistor 14.
An attenuator 16 having a voltage between them as an output signal Vout, and having the same characteristics as the attenuator 16 and dividing the reference voltage Vref between the source 18s-drain 18d of the field effect transistor 18 and the resistor 20 to source 18s-. Drain 1
The attenuator 22 having the voltage between 8d as the output voltage Vmo and the voltage Vg at the gates 12g and 18g of the field effect transistors 12 and 18 so that the output voltage Vmo is proportional to the control voltage Vc.
And a correction circuit 24 for applying Also,
The field effect transistors 12 and 18 are formed on the same semiconductor chip 26.

The field effect transistors 12 and 18 are n-channel MOS type. In the attenuator 16, the source 12s-drain 12d of the field effect transistor 12 is connected in parallel to the signal line 30 between the input and output, and the resistor 14 is connected in series to the signal line 30 on the input side of the field effect transistor 12. Therefore, the input signal Vin is divided between the source 12s and the drain 12d and the resistor 14, and the output signal Vou
t becomes a voltage between the source 12s and the drain 12d. The attenuator 22 has the same configuration as the attenuator 16 except that the reference voltage Vref is input and the output voltage Vmo is output to the correction circuit 24.

The correction circuit 24 comprises a differential amplifier 32 and resistors 34, 36, 38 and 40. The output voltage Vmo is input to the + input terminal 32ip of the differential amplifier 32, and the control voltage Vc is input to the-input terminal 32im.
The output terminal 32o of the differential amplifier 32 is connected to the gates 12g and 18g of the field effect transistors 12 and 18. That is, the voltage Vg of the output terminal 32o is negatively fed back to the + input terminal 32ip via the field effect transistor 18. Note that the resistors 34, 36, 38, 40 all have the same resistance value (for example, 10 kΩ).

Next, the operation of the attenuation circuit 10 will be described. It is assumed that the control voltage Vc is changed to Vc> Vmo. Then, the voltage V of the output terminal 32o of the differential amplifier 32 is
g, that is, the gate voltage V of the field effect transistor 18
The decrease of g increases the resistance value between the source 18s and the drain 18d of the field effect transistor 18, and as a result, the output voltage Vmo increases and Vc = Vmo. On the contrary, it is assumed that the control voltage Vc is changed to Vc <Vmo. Then, as the gate voltage Vg increases, the resistance value between the source 18s and the drain 18d decreases, and as a result, the output voltage Vmo decreases and Vc = Vmo. Thus, the control voltage Vc is proportional to the output voltage Vmo. Further, the attenuators 16 and 22 have the same characteristics, and the same voltage Vg is applied to the gates 12g and 18g of the field effect transistors 12 and 18 by the correction circuit 24.
Therefore, the resistance value between the source 12s and the drain 12d of the field effect transistor 12 changes in proportion to the control voltage Vc. That is, the amount of attenuation proportional to the control voltage Vc is obtained.

When the output voltage Vmo is about to change due to temperature change, the gate voltage Vg changes to Vg + ΔVg so that Vc = Vmo is satisfied. At this time, since the attenuators 16 and 22 have the same characteristics, the characteristics of the attenuator 16 also change depending on the temperature, like the attenuator 22. And
The gate voltage Vg + ΔVg also applies to the field effect transistor 12.
Is applied, the amount of attenuation is constant even when the temperature changes. In order to further enhance this effect, it is desirable that the field effect transistors 12 and 18 or the resistors 14 and 20 are thermally coupled as close to each other as possible. If possible, it is desirable to form at least the field effect transistors 12 and 18 on the same semiconductor chip 26 as in this embodiment.

In this embodiment, the proportional constant between the control voltage Vc and the output voltage Vmo is set to 1. A desired value can be obtained for this constant of proportionality by setting the resistance values of the resistors 34, 36, 38 and 40 to appropriate values. The field effect transistors 12 and 18 may be p-channel MOS type, junction type field effect transistors, or the like, or may not be formed on the same semiconductor chip 26 but may be individual parts. Also, the field effect transistors 12, 1
In addition to 8, the resistors 14 and 20 are the same semiconductor chip 26
It may be formed on top. In this case, the characteristics of the resistors 14 and 20 can be easily made the same.

[0016]

According to the attenuating circuit of the present invention, the attenuation amount proportional to the control voltage can be obtained without the need for adjustment, so that the handling can be facilitated. Further, since the signal line between the input and the output does not have a capacitor connected in series, it can operate at a low frequency including direct current. Further, the characteristics of the first and second attenuators change in the same manner due to the change in temperature, and since the same gate voltage is applied to the first and second field effect transistors, they can be controlled in a wide operating temperature range. The amount of attenuation proportional to the voltage can be obtained with high accuracy.

If at least the first and second field effect transistors are formed on the same semiconductor chip, the characteristics of the first and second attenuators can be easily made the same.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an attenuation circuit according to the present invention.

FIG. 2 is a circuit diagram showing a conventional attenuation circuit.

FIG. 3 is a graph showing a relationship between a control voltage of a PIN diode and an attenuation amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Attenuation circuit 12 ... 1st field effect transistor 14 ... 1st resistor 16 ... 1st attenuator 18 ... 2nd field effect transistor 20 ... 2nd resistor 22 ... 2nd attenuator 24 ... Correction circuit 26 ... Semiconductor chip

Claims (2)

[Claims] 1. A first attenuator which divides an input signal between a source and a drain of a first field effect transistor and a first resistor to output a voltage between the source and the drain as an output signal, and A second attenuator having the same characteristics as the attenuator and dividing the reference voltage between the source-drain of the second field effect transistor and the second resistor to use the voltage between the source-drain as an output voltage. And a correction circuit for applying a voltage to the gates of the first and second field effect transistors so that the output voltage of the attenuator is proportional to the control voltage. 2. The attenuation circuit according to claim 1, wherein at least the first and second field effect transistors are formed on the same semiconductor chip.