JPH07249955A - Distortion reduced variable attenuator - Google Patents

Abstract

PURPOSE:To obtain a distortion-reduced variable attenuator by inputting signals having mutuall reversed phases to two pin diode attenuators (PDAs) and mutually offsetting secondary distortion components generated from the PDAs. CONSTITUTION:An input signal is converted into a balanced type signal by an unbalance/balance circuit 1. When a balanced output on the side of a PDA 3 is set up to earth in the circuit 1, a signal having the same phase as the input signal appears on a balanced output on the side of a PDA 2. When the balanced output on the PDA 2 side is set up to the earth, a signal with reverse phase to the input signal appears in the balanced output on the PDA 3 side. Since signals with mutually reversed phases are outputted from the output terminals of the PDAs 2, 3, these signals are converted into balanced type signals. Thereby secondary distortion components generated in the PDAs 2, 3 are mutually offset and a signal attenuated by a prescribed value is outputted from the circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low distortion variable attenuator which greatly reduces secondary distortion and performs attenuation variable operation.

[0002]

2. Description of the Related Art An AGC (automatic gain control circuit) is used when a received electric field is constantly changing, such as a car radio or satellite receiver, and a variable attenuator is used for this AGC. . FIG. 2 is a circuit diagram showing a configuration of a conventional variable attenuator, and the variable attenuator shown in FIG. 2 is called a π type pin diode attenuator. In the figure, capacitors 5, 6 and 7 are capacitors for cutting direct current, and a capacitor 8 is a capacitor for grounding in an alternating current. In the π type pin diode attenuator having such a configuration, the bias voltage Vbia is
When the control voltage Vcont is changed while s is applied, the current flowing through the pin diode 13 and the resistor 10 changes, the differential resistance of the pin diode 13 changes, and its impedance changes. In this case, the passage loss increases as the impedance of the pin diode 13 increases. When the current flowing through the resistor 10 changes, the potential at the connection point between the pin diode 13 and the resistor 10 changes, and the current flowing through the resistor 9 and the pin diodes 12 and 14 changes.
The impedance of the pin diodes 12 and 14 changes. Therefore, the impedance of the pin diodes 12 and 14 can be changed to match the input and output impedances.

In this way, according to the conventional π-type pin diode attenuator shown in FIG. 2, the attenuation amount can be adjusted while matching the input / output impedance.

[0004]

However, in the above-mentioned conventional π-type pin diode attenuator, the second-order distortion is generated based on the non-linear characteristic of the VI characteristic of the pin diode 13 which changes the passage loss. It cannot be used when circuit distortion of a predetermined amount or less is required.

The present invention has been made based on the output characteristics of the conventional π-type pin diode attenuator as described above, and the purpose thereof is to significantly reduce the secondary distortion and adjust the attenuation amount. To provide a low distortion variable attenuator.

[0006]

In order to achieve the above object, the present invention provides a first unbalanced / balanced circuit and an input terminal connected to one output terminal of the first unbalanced / balanced circuit. A first pin diode attenuator, a second pin diode attenuator having an input terminal connected to the other output terminal of the first unbalanced / balanced circuit, and an output terminal of the first pin diode attenuator. A second unbalanced circuit connected to one input terminal, the output terminal of the second pin diode attenuator being connected to the other input terminal.
And a balance circuit.

[0007]

With this configuration, when a signal is input to the first unbalanced / balanced circuit, when the balanced output on the second pin diode attenuator side is set to the ground side, the balanced on the first pin diode attenuator side is set. When the output of the same phase as the input is obtained and the balanced output of the first pin diode attenuator side is set to the ground side, the balanced output of the second pin diode attenuator side has the output of the opposite phase to the input. can get. Therefore, the signal having the same phase as the input signal is input to the first pin diode attenuator, and the second pin attenuator
A signal having a phase opposite to that of the input signal is input to the pin diode attenuator of, and the input signals are output in opposite phases from the first pin diode attenuator and the second pin diode attenuator, and the secondary distortion is It is output in the same phase. Then, the output signal of the first pin diode attenuator and the output signal of the second pin diode attenuator are unbalanced output by the second unbalanced / balanced circuit,
The secondary distortions generated in the first pin diode attenuator and the second pin diode attenuator are offset and reduced with respect to each other, so that the attenuation amount is adjusted in a state in which the distortion component of the output signal is significantly reduced.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram showing the configuration of this embodiment.

As shown in the figure, one end of a primary winding 1a of a first unbalanced / balanced circuit 1 using a transformer is grounded, and one end of a secondary winding 1b is connected to a first pin diode attenuator 2 Input terminal of the second pin diode attenuator 3 is connected to the other end. The output terminal of the first pin diode attenuator 2 and the output terminal of the second pin diode attenuator 3 are connected to both ends of the primary winding 4a of the second unbalanced / balanced circuit 4 using a transformer. One end of the secondary winding 4b of the second unbalanced / balanced circuit 4 is grounded. Here, as the first pin diode attenuator 2 and the second pin diode attenuator 3, the π type pin diode attenuator already described with reference to FIG. 2 is used, and both pin diode attenuators are
They are driven under the same operating conditions.

The first unbalanced / balanced circuit 1 converts an input signal input to the primary winding 1a of the unbalanced type into a balanced type, and a balanced type first pin diode attenuator 2;
It drives the second pin diode attenuator 3 and
An unbalanced type of signal is output by the unbalanced / balanced circuit 4 of the first pin diode attenuator 2
And has a function of canceling and reducing the secondary distortion generated in the second pin diode attenuator 3.

Next, the operation of this embodiment having such a configuration will be described. When a signal is input in this embodiment, the input signal is converted into a balanced type by the first unbalance / balance circuit 1. In the first unbalanced / balanced circuit 1, when the balanced output on the second pin diode attenuator 3 side is set to ground, the balanced output on the first pin diode attenuator 2 side has the same phase as the input signal. Signal appears. When the balanced output on the first pin diode attenuator 2 side is set to ground, a signal having a phase opposite to the input signal appears on the balanced output on the second pin diode attenuator 3 side.

Therefore, a signal having the same phase as the input signal is input to the first pin diode attenuator 2, and a signal having a phase opposite to the input signal is input to the second pin diode attenuator 3. In this case, the output signals of the first pin diode attenuator 2 and the second pin diode attenuator 3 output the input signals that have been attenuated by the predetermined phases, respectively, and are simultaneously generated by the respective pin diode attenuators. Second-order distortion is output in phase. In this way, the output signal of the first pin diode attenuator 2 and the output signal of the second pin diode attenuator 3 which have undergone predetermined attenuation, the second-order distortion of the first pin diode attenuator 2 and the second pin The second-order distortion of the diode attenuator 3 is converted into an unbalanced type by the second unbalanced / balanced circuit 4. In this case, the second unbalanced / balanced circuit 4
Then, since the potential difference between the two balanced inputs from the first pin diode attenuator 2 and the second pin diode attenuator 3 is unbalancedly output, the second unbalanced / balanced circuit 4
The output signal of the first pin diode attenuator 2
The secondary distortions generated in the second pin diode attenuator 3 cancel each other and the distortion component is significantly reduced, and the signal attenuation is adjusted.

As described above, according to this embodiment, the first unbalanced / balanced circuit 1 inputs the signal having the same phase as the input signal to the first pin diode attenuator 2 and the second pin diode attenuator 3. Is input with a signal opposite in phase to the input signal, and by the second unbalance / balance circuit 4,
The second-order distortions generated in the first pin diode attenuator 2 and the second pin diode attenuator 3 cancel each other out, and the second unbalanced / balanced circuit 4 outputs an output signal that has undergone a predetermined attenuation. To be done. For this reason, according to the present embodiment, distortion in the first pin diode attenuator 2 and the second pin diode attenuator 3 can be significantly reduced, and highly accurate adjustment of the attenuation amount becomes possible.

[0014]

According to the present invention, a signal having the same phase as the input signal is input to the first pin diode attenuator and the input signal is input to the second pin diode attenuator by the first unbalance / balance circuit. A signal having a phase opposite to that of the input signal is input, and the second unbalanced / balanced circuit cancels the secondary distortions generated in the first pin diode attenuator and the second pin diode attenuator. It becomes possible to adjust the amount of attenuation with a high degree of accuracy while significantly reducing.

[Brief description of drawings]

 ■

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional variable attenuator.

[Explanation of symbols]

 1 1st unbalanced / balanced circuit 2 1st pin diode attenuator 3 2nd pin diode attenuator 4 2nd unbalanced / balanced circuit

Claims (2)

[Claims] 1. A first unbalanced / balanced circuit, a first pin diode attenuator having an input terminal connected to one output terminal of the first unbalanced / balanced circuit, and the first unbalanced circuit. A second pin diode attenuator having an input terminal connected to the other output terminal of the balanced circuit, and an output terminal of the first pin diode attenuator connected to one input terminal of the second pin diode attenuator A second unbalanced output terminal connected to the other input terminal
A low distortion variable attenuator having a balanced circuit. 2. The low distortion variable attenuator according to claim 1, wherein the first pin diode attenuator and the second pin diode attenuator are π type pin diode attenuators.