JP2004228710A - Variable attenuation circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable attenuation circuit with an excellent temperature characteristic. <P>SOLUTION: The variable attenuation circuit VATT is provided with: a serial side current control circuit SCON for controlling a control current supplied to a serial side PIN diode DS; and a parallel side current control circuit PCON for controlling a control current supplied to parallel side PIN diodes DP1, DP2. The variable attenuation circuit with the excellent temperature characteristic can be realized because the attenuation of a π type attenuator ATT is almost unchanged with a temperature change although the resistance itself of the PIN diodes DS, DP1, DP2 is changed with the temperature change by individually controlling the control current supplied to the serial side PIN diode DS and the parallel side PIN diodes DP1, DP2. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a variable attenuator, and more particularly to a variable attenuator in which the amount of attenuation changes when a current flowing through a PIN diode changes.
[0002]
Problems to be solved by the prior art and the invention
In a variable attenuation circuit, a PIN diode is used to make the amount of attenuation of a high-frequency signal variable. An example of a variable attenuation circuit using the PIN diode is disclosed in Non-Patent Document 1. In this variable attenuation circuit, the voltage applied to the series PIN diode connected in series between the input and output is fixed, and the voltage applied to the parallel PIN diode connected in parallel between the input and output is changed. Since the current flowing through the series PIN diode and the parallel PIN diode flows through a common load resistance, the current flowing through the series PIN diode and the current flowing through the parallel PIN diode are changed by changing the voltage applied to the parallel PIN diode. Can be changed, and the amount of attenuation of the high-frequency signal can be changed. However, in this variable attenuation circuit, the current flowing through the PIN diode changes with the temperature change because the voltage drop at the PIN diode changes with the temperature change. Therefore, this variable attenuation circuit has a temperature characteristic in which the amount of attenuation changes in accordance with a change in temperature, and there has been a problem that it is difficult to control the amount of attenuation accurately. Therefore, an object of the present invention is to provide a variable attenuation circuit having excellent temperature characteristics. As examples of the variable attenuation circuit, those disclosed in JP-A-8-78993 (Patent Document 1) and JP-A-10-163785 (Patent Document 2) are further disclosed.
[0003]
[Patent Document 1]
JP-A-8-78993 [Patent Document 2]
JP-A-10-163785 [Non-Patent Document 1]
"High-frequency circuit classroom", [online], [searched on January 6, 2003], Internet <URL: http: // www1. sphere. ne. jp / i-lab / ilab / kairo / k5 / k5_4b. htm>
[0004]
[Means for Solving the Problems]
To achieve such an object, the variable attenuation circuit according to the first aspect of the present invention includes a series PIN diode connected in series between the input and output, a parallel PIN diode connected in parallel between the input and output, A variable attenuation circuit comprising: a series-side current control circuit that controls a control current flowing through a series-side PIN diode; and a parallel-side current control circuit that controls a control current that flows through a parallel-side PIN diode. By individually controlling the control current flowing through the parallel-side PIN diode, the amount of attenuation of the high-frequency signal between the input and output is controlled.
[0005]
According to the present invention, a series-side current control circuit that controls a control current that flows through a series-side PIN diode, and a parallel-side current control circuit that controls a control current that flows through a parallel-side PIN diode are provided. By individually controlling the control current flowing through the parallel-side PIN diode, a variable attenuation circuit having excellent temperature characteristics can be realized.
[0006]
A variable attenuation circuit according to a second aspect of the present invention is the circuit according to the first aspect of the invention, wherein a π-type attenuation circuit including a series PIN diode and a parallel PIN diode is formed in the variable attenuation circuit. A control signal for controlling the amount of attenuation is input to both the series-side current control circuit and the parallel-side current control circuit, and the control signal in the series-side current control circuit is supplied to the series-side PIN diode. The characteristic between the current and the current is determined based on the characteristic between the series PIN diode resistance value and the attenuation in the π-type attenuation circuit so that the control signal and the attenuation are substantially linear within a predetermined attenuation range. The characteristic between the control signal in the parallel-side current control circuit and the control current flowing through the parallel-side PIN diode is substantially linear when the control signal and the attenuation amount are within a predetermined attenuation range. Thus, the characteristic is set based on the characteristic between the parallel-side PIN diode resistance value and the amount of attenuation in the π-type attenuation circuit.
[0007]
According to this configuration, the characteristic between the control signal in the series-side current control circuit and the control current flowing through the series-side PIN diode and the characteristic between the control signal in the parallel-side current control circuit and the control current flowing through the parallel-side PIN diode Is set such that the control signal and the attenuation amount become substantially linear within a predetermined attenuation range, so that a good VSWR can be obtained.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter, referred to as embodiments) will be described with reference to the drawings.
[0009]
FIG. 1 is a circuit block diagram showing a configuration of an automatic gain control amplifier circuit including a variable attenuation circuit according to an embodiment of the present invention. The automatic gain control amplifier circuit according to the present embodiment is a circuit for controlling the level of the high-frequency signal at the output terminal OUT to match the specified level even if the level of the high-frequency signal at the input terminal IN fluctuates. An attenuator VATT, an amplifier AMP, a detector DET and a comparator COM are provided. The variable attenuation circuit VATT includes a π-type attenuator ATT, a series current control circuit SCON, and a parallel current control circuit PCON.
[0010]
The high-frequency signal input to the input terminal IN is first input to the π-type attenuator ATT to attenuate the signal. The attenuated high-frequency signal is then input to the amplifier AMP to amplify the signal. The amplified high-frequency signal is output to the output terminal OUT.
[0011]
The detector DET detects the level of the high-frequency signal at the output terminal OUT, and outputs a voltage indicating the detected level. The comparator COM compares the output voltage from the detector DET with a specified voltage indicating a specified level, and outputs a control voltage for controlling the amount of attenuation in the π-type attenuator ATT.
[0012]
In the series-side current control circuit SCON, a control voltage from the comparator COM is input, and a control current flowing through the series-side PIN diode DS is output. In the parallel-side current control circuit PCON, a control voltage from the comparator COM is input, and a control current flowing through the parallel-side PIN diodes DP1 and DP2 is output.
[0013]
In the π-type attenuator ATT, a series PIN diode DS is connected in series between its input and output, and parallel PIN diodes DP1 and DP2 are connected in parallel between its input and output. Then, the control current from the series side current control circuit SCON flows to the series side PIN diode DS, and the control current from the parallel side current control circuit PCON flows to the parallel side PIN diodes DP1 and DP2. When the control current flowing through the PIN diodes DS, DP1, DP2 changes, the resistance values of the PIN diodes DS, DP1, DP2 change, and the attenuation in the π-type attenuator ATT changes. Therefore, by controlling the current flowing through the series PIN diode DS and the parallel PIN diodes DP1 and DP2 by the series current control circuit SCON and the parallel current control circuit PCON, respectively, the level of the high-frequency signal at the output terminal OUT becomes the specified level. The attenuation of the high-frequency signal in the π-type attenuator ATT is controlled so that
[0014]
Next, characteristics of the PIN diodes DS, DP1, DP2 and the π-type attenuator ATT will be described.
[0015]
FIG. 2 shows the results of calculating the transfer characteristics of the π-type attenuator ATT when the temperature is changed by + 50 ° C. and −50 ° C. with respect to the standard value (indicated by type) using the π-type attenuator model shown in FIG. FIG. However, when calculating the transfer characteristic, as shown in the π-type attenuator model in FIG. 3, the series PIN diode DS and the parallel PIN diodes DP1 and DP2 are modeled by the resistance Rs and the resistance Rp, respectively, and the input / output impedance is calculated. Is Z0. Then, the temperature characteristic of the PIN diode resistance value is set to 3300 ppm / ° C., and when calculating the transfer characteristic, the resistance values of the resistors Rs and Rp are changed at a ratio to the temperature change. In the π-type attenuator model of FIG. 3, the input voltage to the model is V1, the input voltage to the resistor Rs is V2, and the output voltage of the model is V3.
[0016]
As shown in FIG. 2, the transfer characteristics V2 / V1 and the transfer characteristics V3 / V2 change with a change in temperature. However, while the value of the transfer characteristic V2 / V1 decreases with an increase in temperature, the value of the transfer characteristic V3 / V2 increases with an increase in temperature. That is, the direction of the temperature characteristic is opposite in the transfer characteristic V2 / V1 and the transfer characteristic V3 / V2. Therefore, the value of the transfer characteristic V3 / V1 hardly changes with respect to the temperature change as shown in FIG. 2 because the temperature characteristic in the transfer characteristic V2 / V1 and the temperature characteristic in the transfer characteristic V3 / V2 cancel each other. . This means that if the current flowing through PIN diodes DS, DP1, and DP2 does not change with temperature, the resistance values of PIN diodes DS, DP1, and DP2 change with temperature, but π-type attenuator ATT Indicates that the amount of attenuation hardly changes with a change in temperature. Therefore, the temperature characteristics of the π-type attenuator ATT can be improved by individually controlling the control current flowing through the series PIN diode DS and the control current flowing through the parallel PIN diodes DP1 and DP2.
[0017]
Therefore, the variable attenuation circuit VATT according to the present embodiment includes a series current control circuit SCON that controls a control current flowing through the series PIN diode DS, and a parallel current control that controls a control current that flows through the parallel PIN diodes DP1 and DP2. And a circuit PCON for individually controlling the control current flowing through the series-side PIN diode DS and the parallel-side PIN diodes DP1 and DP2.
[0018]
FIG. 4 is a diagram showing current-resistance characteristics of the PIN diodes DS, DP1, and DP2. In FIG. 4, both the current axis and the resistance axis are shown on a logarithmic scale. In the characteristics shown in FIG. 4, when the current becomes x times, the resistance becomes about 1 / x times, so that the current-resistance characteristics of the PIN diodes DS, DP1, and DP2 can be approximated in an inversely proportional relationship.
[0019]
FIG. 5 is a diagram showing a result of calculating a characteristic between the amount of attenuation and the control current in the π-type attenuator ATT. This characteristic can be calculated by using a known relational expression between the resistance value and the attenuation amount regarding the π-type attenuator ATT shown in the following equations (1) and (2).
(Equation 1)
Rs = Z0 / 2 × (10 ^{L / 10} −1) / 10 ^{L / 20} (1)
(Equation 2)
Rp = Z0 × (10 ^{L / 20} +1) / (10 ^{L / 20} −1) (2)
[0020]
Here, Rs is the resistance of the series PIN diode DS, Rp is the resistance of the parallel PIN diodes DP1 and DP2, Z0 is the input / output impedance, and L is the attenuation (dB). In calculating the characteristics shown in FIG. 5, the current-resistance characteristics of the PIN diodes DS, DP1, and DP2 are approximated in an inversely proportional relationship from the results shown in FIG.
[0021]
The calculation results shown in FIG. 5 show the characteristics of the current flowing through the series-side PIN diodes DS and the current flowing through the parallel-side PIN diodes DP1 and DP2, which are necessary to obtain a desired attenuation without deteriorating the VSWR. Here, consider a control voltage-control current characteristic in which the horizontal axis in the characteristic of FIG. 5 is replaced by the control voltage from the comparator COM. The control current flowing through the series-side PIN diode DS and the control current flowing through the parallel-side PIN diodes DP1 and DP2 by the series-side current control circuit SCON and the parallel-side current control circuit PCON are controlled so as to match the control voltage-control current characteristics. If possible, the relationship between the control voltage and the attenuation (dB) can be made substantially linear, and a good VSWR can be obtained.
[0022]
Also, the calculation result shown in FIG. 5 indicates that the control current flowing through the series PIN diode DS needs to be increased about 1 / x times in order to increase the attenuation (dB) by x times. The characteristics between the attenuation (dB) and the control current flowing through the series PIN diode DS can be approximated in an inversely proportional relationship. Further, the calculation result shown in FIG. 5 indicates that the characteristic between the attenuation (dB) and the control current flowing through the parallel-side PIN diodes DP1 and DP2 is non-linear such that the slope of the control current / attenuation decreases as the attenuation increases. The result is a characteristic. However, in the range where the amount of attenuation is equal to or less than a predetermined value, the characteristic between the amount of attenuation (dB) and the control current flowing through the parallel PIN diodes DP1 and DP2 can be approximated by linear characteristics.
[0023]
In the present embodiment, based on the above results, the control voltage-control current characteristic of the series-side current control circuit SCON is set to be inversely proportional, and the control voltage-control current characteristic of the parallel-side current control circuit PCON is set to be proportional. ing. As a result, the relationship between the control voltage and the attenuation (dB) can be made substantially linear in the range where the attenuation is equal to or less than the predetermined value, and a good VSWR can be obtained. Hereinafter, an example of the configuration of the series current control circuit SCON and the parallel current control circuit PCON will be described.
[0024]
First, an example of the configuration of the series current control circuit SCON will be described with reference to FIG. The series current control circuit SCON includes pnp transistors Q1, Q2, Q3, Q4, an operational amplifier OPAmp1, and a constant current source Iref.
[0025]
The pnp transistor Q1 has a base Q1b connected to one end of the constant current source Iref, and a collector Q1c connected to one end of the resistor R1. The other end of the resistor R1 and the other end of the constant current source Iref are grounded. The pnp transistor Q2 has its base Q2b connected to the emitter Q1e of the pnp transistor Q1, and its emitter Q2e connected to the reference constant voltage Vcc. The pnp transistor Q3 has its base Q3b and collector Q3c connected, and its emitter Q3e connected to the reference constant voltage Vcc and the emitter Q2e of the pnp transistor Q2. The pnp transistor Q4 has its base Q4b and collector Q4c connected to the constant current source Iref and the base Q1b of the pnp transistor Q1, and its emitter Q4e connected to the base Q3b and collector Q3c of the pnp transistor Q3.
[0026]
The operational amplifier OPAmp1 has a non-inverting input terminal supplied with the voltage VIN, an inverting input terminal connected to the collector Q1c of the pnp transistor Q1 and one end of the resistor R1, and an output terminal having the emitters Q1e and pnp of the pnp transistor Q1. It is connected to the base Q2b of the transistor Q2.
[0027]
Here, the characteristics between the base-emitter voltage and the collector current of the pnp transistors Q1, Q2, Q3, Q4 are substantially the same.
[0028]
Next, the relationship between input and output in the circuit shown in FIG. 6 will be described. In the circuit shown in FIG. 6, the control voltage VIN from the comparator COM is input to the non-inverting input terminal of the operational amplifier OPAmp, and the current Ib is output from the collector Q2c of the pnp transistor Q2. This current Ib becomes a control current flowing through the series PIN diode DS.
[0029]
Generally, the relationship between the base-emitter voltage VBE of a bipolar transistor and the collector current Ic is represented by the following (3) from the pn junction characteristic.
[Equation 3]
VBE = K × T / q × log (Ic / Is) (3)
[0030]
Here, Is is the saturation current of the transistor, q is the charge of electrons, K is Boltzmann's constant, and T is the junction temperature.
[0031]
In the circuit shown in FIG. 6, the following equation (4) holds for the base-emitter voltages VBE1, VBE2, VBE3, and VBE4 of the pnp transistors Q1, Q2, Q3, and Q4.
(Equation 4)
VBE1 + VBE2 = VBE3 + VBE4 (4)
[0032]
Here, assuming that the collector current of the pnp transistor Q1 is Ia, the collector current of the pnp transistor Q2 is Ib, and the collector currents of the pnp transistors Q3 and Q4 are Ic, the pn junction equation of the equation (3) is applied to the equation (4). Then, the following equation (5) is obtained.
(Equation 5)
K × T / q × (log (Ia / Is) + log (Ib / Is))
= 2 × K × T / q × log (Ic / Is) (5)
[0033]
By transforming equation (5), the following equation (6) is obtained.
(Equation 6)
Ib = Ic ² / Ia (6)
[0034]
Equation (6) shows that the collector current Ia of the pnp transistor Q1 and the collector current Ib of the pnp transistor Q2 are in inverse proportion. Further, the equation (6) has no temperature characteristic because the constant term in the inverse proportional relationship is only Ic.
[0035]
Here, the output terminal of the operational amplifier OPAmp is connected to the inverting input terminal of the operational amplifier OPAmp via the emitter and the collector of the pnp transistor Q1, so that the input voltage VIN to the non-inverting input terminal of the operational amplifier OPAmp and pnp There is a proportional relationship with the collector current Ia of the transistor Q1. Therefore, the input voltage VIN to the non-inverting input terminal of the operational amplifier OPAmp is inversely proportional to the collector current Ib of the pnp transistor Q2.
[0036]
With the series-side current control circuit SCON having the above configuration, the control voltage-control current characteristics of the series-side current control circuit SCON can be set in an inversely proportional relationship. Further, a circuit having excellent temperature characteristics can be realized.
[0037]
Next, an example of the configuration of the parallel-side current control circuit PCON will be described with reference to FIG. The parallel-side current control circuit PCON includes an operational amplifier OPAmp2 and an npn transistor Q5.
[0038]
The operational amplifier OPAmp2 has a non-inverting input terminal to which a control voltage from the comparator COM is input via a resistor R3, and an inverting input terminal which is grounded via a resistor R2. As for the npn transistor Q5, its base Q5b is connected to the output terminal of the operational amplifier OPAmp2, and its collector Q5c is connected to the reference constant voltage Vcc. A current flowing from the emitter Q5e of the npn transistor Q5 to the parallel PIN diodes DP1 and DP2 via the resistor R6 is output. The emitter Q5e of the npn transistor Q5 is connected to the inverting input terminal of the operational amplifier OPAmp2 via the resistor R4, and further connected to the non-inverting input terminal of the operational amplifier OPAmp2 via the resistors R6 and R5. With the parallel current control circuit PCON having the above configuration, the control voltage-control current characteristics of the parallel current control circuit PCON can be set in a proportional relationship. Further, a circuit having excellent temperature characteristics can be realized.
[0039]
In the present embodiment, a series current control circuit SCON that controls a control current flowing through the series PIN diode DS, and a parallel current control circuit PCON that controls a control current that flows through the parallel PIN diodes DP1 and DP2 are provided. ing. By individually controlling the control currents flowing through the series-side PIN diodes DS and the parallel-side PIN diodes DP1 and DP2, the resistance values of the PIN diodes DS, DP1 and DP2 change with temperature, but the π-type The attenuation of the attenuator ATT hardly changes with a change in temperature. Therefore, a variable attenuation circuit having excellent temperature characteristics can be realized.
[0040]
Further, in the present embodiment, the control voltage-control current characteristic and the parallel-side current control of the series-side current control circuit SCON are calculated from the calculation result of the characteristic between the attenuation and the control current in the π-type attenuator ATT shown in FIG. A control voltage-control current characteristic of the circuit PCON is set. More specifically, the control voltage-control current characteristic of the series-side current control circuit SCON is set to have an inverse proportional relationship, and the control voltage-control current characteristic of the parallel-side current control circuit PCON is set to have a proportional relationship. Have been. Therefore, the relationship between the control voltage and the attenuation (dB) can be made substantially linear in the range where the attenuation is equal to or less than the predetermined value, and a good VSWR can be obtained.
[0041]
FIG. 8 shows experimental results obtained by the variable attenuation circuit according to the present embodiment. However, FIG. 8 shows the control voltage-attenuation characteristic when the temperature is changed when the series-side current control circuit SCON and the parallel-side current control circuit PCON have the configurations shown in FIGS. 6 and 7, respectively. As shown in FIG. 8, a variable attenuation circuit in which the attenuation does not substantially change in response to a temperature change in a range where the attenuation is about 33 dB or less was obtained. Further, the relationship between the control voltage and the attenuation (dB) could be made substantially linear in the range where the attenuation was about 33 dB or less.
[0042]
The attenuator to which the present invention can be applied is not limited to the π-type attenuator. For example, the present invention can be applied to any attenuator having a series PIN diode and a parallel PIN diode such as a T-type attenuator. As an example, a result of calculating the transfer characteristic of the T-type attenuator in the same manner as in the case of the π-type attenuator will be described below.
[0043]
FIG. 9 shows the results of calculating the transfer characteristics of a T-type attenuator using the T-type attenuator model shown in FIG. 10 when the temperature is changed by + 50 ° C. and −50 ° C. with respect to a standard value (indicated by type). FIG. In the T-type attenuator model shown in FIG. 10, the input voltage to the model is V1, the input voltage to the resistor Rs is V2, and the output voltage of the model is V4.
[0044]
In the calculation results shown in FIG. 9, as in the case of the π-type attenuator, the direction of the temperature characteristic is opposite in the transfer characteristics V2 / V1 and the transfer characteristic V4 / V2. Therefore, the temperature characteristic in the transfer characteristic V2 / V1 and the temperature characteristic in the transfer characteristic V4 / V2 cancel each other, and the value of the transfer characteristic V4 / V1 hardly changes with the temperature change as shown in FIG. Therefore, similarly to the case of the π-type attenuator, the T-type attenuator can realize a variable attenuation circuit having excellent temperature characteristics by individually controlling the control current flowing through the series-side PIN diode and the parallel-side PIN diode.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram showing a configuration of an automatic gain control amplifier circuit including a variable attenuation circuit according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a result of calculating transfer characteristics using a π-type attenuator model.
FIG. 3 is an equivalent circuit diagram showing a π-type attenuator model.
FIG. 4 is a diagram showing current-resistance characteristics of a PIN diode.
FIG. 5 is a diagram showing a result of calculating characteristics between an amount of attenuation and a control current in the π-type attenuator ATT.
FIG. 6 is a circuit diagram showing an example of a configuration of a series current control circuit.
FIG. 7 is a circuit diagram illustrating an example of a configuration of a parallel-side current control circuit.
FIG. 8 is a diagram showing an experimental result by the variable attenuation circuit according to the embodiment of the present invention.
FIG. 9 is a diagram showing a result of calculating transfer characteristics using a T-type attenuator model.
FIG. 10 is an equivalent circuit diagram showing a T-type attenuator model.
[Explanation of symbols]
AMP amplifier, ATT π-type attenuator, COM comparator, DET detector, DP1, DP2 parallel PIN diode, DS serial PIN diode, PCON parallel current control circuit, SCON serial current control circuit, VATT variable attenuation circuit.

Claims (2)

A series-side PIN diode connected in series between the input and output,
A parallel-side PIN diode connected in parallel between the input and output;
A series side current control circuit for controlling a control current flowing through the series side PIN diode;
A parallel-side current control circuit for controlling a control current flowing through the parallel-side PIN diode;
A variable attenuation circuit comprising
A variable attenuation circuit characterized in that an amount of attenuation of a high-frequency signal between input and output is controlled by individually controlling control currents flowing through a series-side PIN diode and a parallel-side PIN diode. The variable attenuation circuit according to claim 1, wherein
A π-type attenuation circuit including a series PIN diode and a parallel PIN diode is formed in the variable attenuation circuit,
A control signal for controlling the amount of attenuation is input to both the series-side current control circuit and the parallel-side current control circuit,
The characteristic between the control signal in the series-side current control circuit and the control current flowing through the series-side PIN diode is such that the control signal and the amount of attenuation are substantially linear within a predetermined attenuation range. Is set based on the characteristic between the series-side PIN diode resistance value and the amount of attenuation at
The characteristic between the control signal in the parallel-side current control circuit and the control current flowing through the parallel-side PIN diode is such that the control signal and the amount of attenuation are substantially linear within a predetermined attenuation range. The variable attenuation circuit is set based on a characteristic between a parallel-side PIN diode resistance value and an attenuation amount in the above.

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