JP2001308668A - Variable attenuation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable attenuation circuit suitable for high frequency signals, which can be fabricated into IC and can set a big signal attenuation ratio by turning on/off of a switch using transistors. SOLUTION: The circuit comprises a first resistance connected between an input terminal and an output terminal, a second resistance with one end connected to the output terminal and the other and grounded to the earth, a base-biased transistor equipped with a collector connected to a power supply terminal and an emitter connected to the output terminal via capacitance and is connected to the input terminal, and a power supply with one end connected to the emitter via the switch and the other end grounded to the earth.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable attenuation circuit used in a device having a wide input level range such as mobile communication, and more particularly, to a variable attenuation circuit which outputs a stable level even if the input level fluctuates. It is about.

[0002]

2. Description of the Related Art Conventionally, in a device such as a wireless LAN or a mobile communication having a wide input level range or a large input level fluctuation, an output level capable of performing a stable operation even if the input level fluctuates. In order to obtain the above, a variable attenuation circuit for high frequency that can switch the amount of signal attenuation by turning on / off a switch is required.

As an example of a conventional variable attenuator, FIG. 5 shows a variable attenuator using a PIN diode, which has a small passing loss and a large attenuation ratio (hereinafter referred to as an attenuation ratio). As shown in FIG. 5, a resistor 201 connected between the input IN and the output OUT and one end of the resistor 201 are connected to the output OUT.
And a resistor 202 having the other end grounded. A capacitor 203, a PIN diode 204, and a capacitor 205 are connected in series with each other.
01 and parallel. Further, inductances 206 and 20 are provided at both ends of the PIN diode 204.
The switch 208 and the control voltage 209 are connected between the inductances 206 and 207.

When the switch 208 is OFF, the PIN
Since no voltage is applied to the diode 204, the diode 204 is opened, and the resistors 201 and 20 are connected between the input IN and the output OUT.
2 becomes an attenuation circuit. Therefore, the input signal is output after being attenuated at an attenuation rate determined by the resistors 201 and 202. When the switch 208 is ON, a voltage is applied to the PIN diode 204 by the control voltage 209, and an internal resistance (not shown) in the PIN diode 204 becomes sufficiently smaller than the resistance 201. The input signal passes through and is output as it is. Therefore, the signal attenuation can be switched simply by operating the switch 208.

[0005]

However, when an IC is used, when a PN diode using a normal silicon bipolar process is used for the variable attenuation circuit, the PN
Since the junction capacitance of the diode is large, a sufficient attenuation ratio cannot be obtained at a high frequency. In order to prevent a high-frequency signal from flowing to the control voltage 209 side, a large inductance 2 which becomes a high impedance is used.
06 and 207 are required, which cannot be mounted in an IC.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to make it possible to easily make an IC by using a transistor.
An object of the present invention is to provide a variable attenuation circuit suitable for a high-frequency signal, which can increase a signal attenuation ratio by ON / OFF of a switch.

[0007]

In order to achieve the above object, a variable attenuation circuit according to the present invention comprises a first resistor connected between an input terminal and an output terminal, and a first resistor connected at one end to an output terminal. A second resistor having a grounded end, a collector connected to the power supply terminal, an emitter connected to the output terminal via the capacitor, a base biased, and a transistor connected to the input terminal; A current source connected to the emitter via the switch and having the other end grounded. With this configuration, an IC can be easily formed, and a large attenuation ratio can be obtained.

A first resistor connected between the input terminal and the output terminal; one end connected to the output terminal and the other end connected to the first terminal;
A second resistor connected to one end of the capacitor, a collector connected to the first power supply terminal, an emitter connected to the output terminal via the second capacitor, a base biased, and an input terminal A first transistor connected to
One end is connected to the emitter via the first switch, the other end is connected to the grounded first current source, the collector is connected to the second power supply terminal, and the emitter is connected to the other end of the first capacitor. A second transistor whose base is biased and grounded via a third capacitor, and a second transistor having one end connected to the emitter of the second transistor via a second switch and the other end grounded. And a current source. With this configuration, an IC can be easily formed, and a large attenuation ratio can be obtained.

A first resistor connected between the input terminal and the output terminal; one end connected to the output terminal and the other end connected to the first terminal;
A second resistor connected to one end of the capacitor, a collector connected to the power supply terminal, an emitter connected to the output terminal via the second capacitor, a base biased, and connected to the input terminal. A first transistor having a collector connected to the power supply terminal, an emitter connected to the other end of the first capacitor, a base biased, and grounded via the third capacitor. A third transistor having a collector connected to the emitter of the first transistor, a base connected to the control voltage input terminal, a collector connected to the emitter of the second transistor, and an emitter connected to the emitter of the third transistor , A reference voltage source having one end connected to the base of the fourth transistor and the other end grounded, and one end connected to the third transistor. The other end is connected to the emitter of the fourth transistor is connected to the emitter of the transistor is characterized in that it has a current source that is grounded. With this configuration, the amount of attenuation can be easily switched by switching the voltage value of the control voltage input to the third transistor.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating the configuration of the variable attenuation circuit according to the first embodiment of the present invention. In the variable attenuator according to the present embodiment, as shown in FIG. 1, an attenuator comprising a resistor 101 and a resistor 102 is connected between an input terminal IN and an output terminal OUT of a signal. And a bypass circuit capable of switching the signal path is connected.

This bypass circuit includes a transistor 104
And a switch 106 and a current source 107,
The collector of the transistor 104 is connected to the power supply terminal 10.
8, the emitter is connected to the output terminal OUT via the capacitor 105. Furthermore, the base is a resistor 103
Are connected to the bias voltage terminal 109 and to the input terminal IN. The current source 107
Are connected to the emitter via a switch 106.

Next, the operation of the variable attenuation circuit will be described with reference to the drawings. This variable attenuator circuit includes a switch 106
Is turned on / off to switch the signal attenuation, and the operation in each case will be described.

[When switch is OFF] Switch 10
When the transistor 6 is OFF, the base of the transistor 104 is supplied with the base potential V _BIAS necessary for operating the transistor from the bias voltage terminal 109.
Since the emitter is not grounded, transistor 104
No current flows through. Therefore, transistor 104
And the potential at point a becomes V _BIAS . In this case, between the input terminal IN and the output terminal OUT, there is only an attenuation circuit including the resistors 101 and 102. Here, the resistance values of the resistor 101 and the resistor 102 are R ₁ and R
_2, and the voltage amplitude at the input terminal IN is P _VIN , the voltage amplitude P _{VOUT at the} output terminal OUT is P _VOUT = ｛R ₂ /
(R ₁ + R ₂ )｝ × P _VIN

[When the Switch is ON] Switch 106
Is ON, a current flows through the transistor 104. Therefore, part of the input signal input from the input terminal IN is output through the transistor 101 and the rest is output through the transistor 104, but is output through the transistor 104 having a smaller resistance value than the resistor 101. There are more signals. At this time, a capacitor 105 is inserted between the emitter of the transistor 104 and the output terminal OUT,
DC components are cut.

Signal via transistor 104 and resistance 1
The signal via 01 is synthesized at the junction of the signals. Here, since this circuit is an emitter follower, the voltage gain is ≒ 1, and if the combined loss due to the phase shift when combining the signals is α, then P _VOUT = P _VIN −α, and the combined loss α is Since the voltage amplitude is sufficiently smaller than P _VIN , the voltage amplitude P _VOUT of the output terminal OUT becomes P _VOUT VINP _VIN .

FIG. 2 shows the voltage amplitude of the output signal when the switch 106 is switched. In FIG. 2, the vertical axis represents the voltage amplitude P of the signal at the output terminal OUT.
_VOUT is shown, and the horizontal axis is ON / OF of the switch 106.
The timing of F is shown. As described above, since the signal does not pass through the transistor 104 when the switch 106 is OFF, the voltage amplitude of the output signal is P _VOUT = ｛R ₂ /
(R ₁ + R ₂ )｝ × P _VIN and switch 106 is turned on
In this case, the voltage amplitude of the output signal is P _VOUT ≒ P _VIN .
As described above, by switching the switch 106, the voltage amplitude of the output signal can be changed.
A large attenuation ratio can be obtained.

Next, another embodiment of the present invention will be described with reference to the drawings. Here, before describing the second embodiment, as a reference example, see FIG. 3 for a variable attenuation circuit in which the resistor 102 can be switched by a switch in addition to the configuration of the first embodiment. I will explain.

In the variable attenuation circuit shown in FIG. 3, the transistor 1 is connected to the resistor 102 of the circuit shown in FIG.
Eleven emitters are connected. Also, the transistor 11
1 is connected to a current source 11 via a switch 112.
3 is also connected. The collector of the transistor 111 is connected to the power supply terminal 117, and the base is connected to the resistor 1
14 is connected to the bias voltage terminal 116 and grounded via the capacitor 115.

Next, the operation of the variable attenuation circuit in two cases by switching the switch 106 and the switch 112 will be described.

[Switch 106 is OFF, switch 11
2 is ON] Since the switch 106 is OFF, the emitter of the transistor 104 is not grounded, and no current flows through the transistor 104. Therefore, the input signal passes through the resistor 101. Further, since the switch 112 is ON, the emitter of the transistor 111 is grounded. Therefore, a current flows through the transistor 111 whose base is biased via the resistor 114, and the resistor 102 is grounded. In this case, between the input terminal IN and the output terminal OUT, there is only an attenuation circuit including the resistors 101 and 102,
The voltage amplitude P _VOUT of the output terminal OUT is P _VOUT = ｛R ₂ /
(R ₁ + R ₂ )｝ × P _VIN

[Switch 106 is ON, switch 112
Is OFF] Since the switch 106 is ON, a current flows through the transistor 104. Therefore, the input terminal IN
A part of the input signal input from the
The rest is output via the transistor 104. Also,
Since the switch 112 is OFF, no current flows through the transistor 111, and the resistor 102 is not grounded, so that it is open.

Therefore, the signal passing through the transistor 104 and the signal passing through the resistor 101 are combined at the junction of the signal and output from the output terminal OUT. Since the combined loss when the signals are combined is sufficiently smaller than P _VIN , the voltage amplitude P _VOUT of the output terminal OUT is P _VOUT ≒ P
It becomes _VIN . Thus, by switching the switches 106 and 112, the voltage amplitude of the output signal can be changed.

Next, as a second embodiment, a specific practical example of the switch 106 and the switch 112 in the above-described reference example will be described with reference to the drawings.
FIG. 4 is a diagram illustrating a configuration of a variable attenuation circuit according to a second embodiment of the present invention. In the variable attenuation circuit according to the present embodiment, as shown in FIG. 4, an attenuation circuit including a resistor 101 and a resistor 102 is connected between a signal input terminal IN and an output terminal OUT, and a signal path is connected to the attenuation circuit. It is configured by connecting a switchable bypass circuit.

The bypass circuit includes a transistor 104. The transistor 104 has a collector connected to the power supply terminal 108 and an emitter connected to the output terminal OUT via the capacitor 105. Further, the base is connected to the power supply terminal 108 via the resistor 103 and to the input terminal IN. The emitter of the transistor 111 is connected to the resistor 102 via the capacitor 110. The collector of the transistor 111 is connected to a power supply terminal 117, and the base is connected to a bias voltage terminal 116 via a resistor 114 and grounded via a capacitor 115.

The collector of the transistor 118 is connected to the emitter of the transistor 104, and the control voltage terminal 119 is connected to the base of the transistor 118. The collector of the transistor 120 is connected to the emitter of the transistor 111, and the reference voltage source 121 is connected to the base of the transistor 120. The current source 122 is connected to the emitter of the transistor 118 and the emitter of the transistor 120.

Next, the operation of the variable attenuation circuit will be described with reference to the drawings. In this variable attenuation circuit, the reference voltage source 1
Control voltage terminal 11 against 21 the voltage value V _ref of
Since the amount of signal attenuation is switched by changing the voltage value V _CONT input from _No. 9, the operation will be described in each case.

[When V _CONT <V _ref ] When the value of V _CONT is V
_When the value is smaller than the value of _ref , the transistor 118 is turned off and the transistor 120 is turned on. Since transistor 118 is OFF, transistor 104 is also O
It becomes an FF, and the input signal passes through the resistor 101. Also,
Since the transistor 120 is ON, the transistor 111 is also ON, and the resistor 102 is grounded in an analog manner. Therefore, a resistor 101 is connected between the input terminal IN and the output terminal OUT.
And an attenuation circuit consisting of the resistor 102, and the voltage amplitude P _VOUT of the output terminal OUT is P _VOUT = ＰR ₂ / (R ₁ + R
₂ )｝ × P _VIN .

[When V _CONT > V _ref ] When the value of V _CONT is V
_When the value is larger than the value of _ref , the transistor 118 is turned on and the transistor 120 is turned off. Since transistor 118 is ON, transistor 104 is also ON
, And part of the input signal is output via the resistor 101 and the rest is output via the transistor 104. Further, since the transistor 120 is OFF, the transistor 111 is also turned off.
F, the resistor 102 is opened without being grounded. Therefore, the signal via the transistor 104 and the resistance 10
The signal via 1 is synthesized and output at the junction of the signals. Since the combined loss at this time is sufficiently smaller than P _VIN , the voltage amplitude P _VOUT of the output terminal OUT is P _VOUT ≒ P
It becomes _VIN . Therefore, the voltage value V of the reference voltage source 121
By changing the voltage value V _CONT input from the control voltage terminal 119 with respect to _ref , the amount of signal attenuation can be easily switched.

[0029]

According to the present invention, since the circuit is composed of a resistor and a transistor, it is easy to make a variable attenuation circuit suitable for high-frequency signals into an IC. Further, since the amount of attenuation is determined by the resistance values of the first and second resistors, a large attenuation amount ratio can be obtained.

Further, the control circuit includes an attenuating circuit comprising first and second resistors and provided between the input and output terminals, a control voltage input terminal, and a reference voltage source, and switches the amount of attenuation according to the voltage value of the control voltage. With this configuration, the amount of attenuation can be easily switched by the control voltage without using a switch.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a change in amplitude of an output voltage signal due to operation of a switch in the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of a variable attenuation circuit according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of a variable attenuation circuit according to a third embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration example of a conventional variable attenuation circuit.

[Explanation of symbols]

101, 102, 105: resistor, 103: bias voltage input terminal, 104: power supply terminal, 106: transistor, 107: capacitance, 108: switch, 109: current source.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J026 AA00 5J098 AA02 AC05 AC09 AC10 AC13 AC19 AC27 AD15 AD17 AD26 EA09 5J100 AA03 AA25 BA02 BB01 BB09 BB11 BB15 BB21 BC03 CA01 CA11 CA18 CA21 CA23 EA02

Claims (3)

[Claims] 1. A first resistor connected between an input terminal and an output terminal, a second resistor having one end connected to the output terminal and the other end grounded, and a collector connected to a power supply terminal. A transistor having an emitter connected to the output terminal via a capacitor, a base biased, and connected to the input terminal; and a current source having one end connected to the emitter via a switch and the other end grounded. And a variable attenuation circuit. A first resistor connected between the input terminal and the output terminal; a second resistor having one end connected to the output terminal and the other end connected to one end of the first capacitor; A first transistor having a collector connected to the first power supply terminal, an emitter connected to the output terminal via a second capacitor, a base biased, and a first transistor connected to the input terminal; A first current source connected to the emitter via one switch and the other end grounded; a collector connected to a second power supply terminal; an emitter connected to the other end of the first capacitor; A second transistor whose base is biased and grounded via a third capacitor; and a second transistor having one end connected to the emitter of the second transistor via a second switch and the other end grounded. Having a current source Variable attenuation circuit to butterflies. 3. A first resistor connected between an input terminal and an output terminal, a second resistor having one end connected to the output terminal and the other end connected to one end of a first capacitor, and a collector. Is connected to the power supply terminal, the emitter is connected to the output terminal via the second capacitor, the base is biased, and the first transistor is connected to the input terminal; and the collector is the power supply terminal. A second transistor having an emitter connected to the other end of the first capacitor, a base biased, and grounded through a third capacitor, and a collector connected to the emitter of the first transistor. A third transistor having a base connected to the control voltage input terminal, a collector connected to the emitter of the second transistor, and an emitter connected to the third transistor. A fourth transistor connected to the emitter of the fourth transistor, a reference voltage source having one end connected to the base of the fourth transistor and the other end grounded, one end connected to the emitter of the third transistor, A current source connected to the emitter of the fourth transistor and having the other end grounded.