JPH07249954A - Step attenuator - Google Patents

Abstract

(57) [Abstract] [Purpose] In a step attenuator that changes the amount of attenuation stepwise to a desired value, I
A high-performance step attenuator suitable for C conversion. [Configuration] FET switch that passes / blocks the input signal
Provide (2,3,4) between the input terminal (1) and the output terminal (5),
Further, fixed attenuators (6, 7, 8) of arbitrary size are installed in parallel with the FET switches (2, 3, 4). FETs are connected in series so that desired attenuation can be obtained.
Select switch (9) to turn it on and off. [Effect] Since the total number of switches and the number of signal passing switches can be configured with a smaller number than before, a step attenuator can be realized with a smaller chip area and less insertion loss.
This is advantageous in terms of high performance and IC.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for setting a high-frequency signal level to a desired value, and in particular, a step of opening and closing a switch by an externally applied DC voltage to change the attenuation amount of the high-frequency signal in steps. Regarding attenuator.

[0002]

2. Description of the Related Art Conventionally, in order to attenuate a high frequency signal in a stepwise manner, a method is used in which a plurality of fixed attenuators having a required attenuation amount are cascaded in advance and a signal is switched to a desired attenuator by a switch. It was being appreciated.

A circuit configuration as shown in FIG. 2 is well known for such a step attenuator.

[0004]

In the case of a three-stage configuration, in the above-mentioned conventional technique, the number of switches per stage is four in order to prevent leakage to the attenuator side and facilitate design of the attenuation amount of the attenuator. It is necessary, and the total number of switches is 12 in the 3-stage configuration.
The number of switches increases, and a signal passes through 6 switches from the input terminal to the output terminal.

A FET FET is generally used as a switch of a type which is operated by a control signal from the outside in a high frequency region. The FET switch has a resistance component (ON resistance) in the ON state, and this ON resistance affects the insertion loss due to the relationship with the input / output impedance and causes a propagation loss. Ideally, 0 is good. Generally, the gate width may be increased to reduce the on-resistance of the FET, but on the other hand, there is a problem that the occupied area of the FET is increased.

Therefore, when the number of switches is large, the number of FETs is also large, which causes a problem that the chip area becomes large when integrated into an IC. In addition, there are many switches between the input terminal and the output terminal of the signal, and there is a problem that the insertion loss due to the ON resistance and the change in the characteristics due to the temperature change become large.

An object of the present invention is to realize a step attenuator in which the number of switches is reduced, the circuit structure is simplified, the chip area when integrated into an IC is reduced, and the ON resistance of the FETs forming the switch section is less likely to be affected. Especially.

[0008]

The above object of the present invention is to provide a switch for passing and blocking an input signal between an input terminal and an output terminal, and further to provide a fixed attenuator of any size in parallel with the switch. Install. This is realized by a step attenuator characterized in that the circuits having the above-mentioned configuration are connected in cascade and each switch is selected and turned on and off so as to obtain a desired attenuation amount.

[0009]

When the configuration of the present invention is used, the number of FET switches is 3 or less in order to obtain one level of attenuation with one stage of attenuator.
(In case of pie type resistance attenuator: 3 pieces, in case of T type resistance attenuator: 2 pieces), resistor is a resistance attenuator (in case of pie type and T type): 3 pieces and resistance for gate protection; 3 pieces Below (6 in case of pie resistance attenuator; 3 in case of T type resistance attenuator; 2 in total) (6 in case of pie resistance attenuator, 6 in case of T type resistance attenuator; 5) However, in the case of the conventional type,
In order to obtain the same level of attenuation, 4 FET switches
Number of resistors, resistance attenuator (for pie type and T type): 3 and resistance for gate protection; 4 in total, 7 in total. Therefore, if FET switches of the same size are used, a step attenuator can be constructed with a smaller chip area and a smaller insertion loss. Further, since the number of switches through which the signal passes is smaller in the present invention, the loss due to impedance mismatch can be reduced.

[0010]

1 is a circuit diagram of a step attenuator according to a first embodiment of the present invention. Although the present invention can be configured with an arbitrary number of fixed attenuators, FIG. 1 illustrates a case where three fixed attenuators are used. Three FET switches (2, 3, 4) connected between the input terminal (1) and the output terminal (5) and their F
Fixed attenuator (6,7,8) individually connected in parallel with ET switch (2,3,4), resistor (9) connected to gate of FET switch (2,3,4), and FET switch It consists of (2,3,4) control terminals (10,11,12).

Here, the attenuation of the fixed attenuator (6) is 4 dB, the attenuation of the fixed attenuator (7) is 8 dB, the attenuation of the fixed attenuator (8) is 16 dB, and the FET switch (2, 3) is used. Input / output impedance is fixed attenuator (6, 7, 8) when (4, 4) is on
The operation for obtaining a specific desired attenuation amount when the impedance is sufficiently lower than the impedance will be described.

For example, if the desired attenuation is 0 dB, the FET
Turn on all switches (2, 3, 4) and input terminals
The signal entering (1) is output to the output terminal (5) through the FET switches (2, 3, 4) having a low impedance. If the desired attenuation is 4 dB, turn off the FET switch (2) and turn on the other FET switches (3, 4), and the input signal will pass through the 4 dB fixed attenuator (6) and then FE
After passing through the T switches (2, 3), an output signal attenuated by 4 dB is obtained at the output. To obtain the maximum attenuation, all the FET switches (2, 3, 4) are turned off and the input signal is passed through all the fixed attenuators (6, 7, 8). In the case of the above circuit configuration, the maximum attenuation amount is 28 dB at the attenuation step of 4 dB. Other attenuation amounts are obtained by combining switches that similarly turn on. The number of steps obtained is as many as 2 to the n-th power, because the number of FET switches to be used (n) is turned on and off.

FIG. 3 is a circuit diagram of a step attenuator circuit according to a second embodiment of the present invention. In the circuit of the first embodiment, when the signal is flowing on the FET switch (9) side, the signal leaks to the fixed attenuator (6, 7, 8) side, and the signal level fluctuates. A circuit in which this is reduced and the accuracy is improved is the second embodiment of FIG. FIG. 3 shows an example using a T-type resistance attenuator. The resistor attenuator consists of pie, T,
There are methods such as H and L types, but in each case one or more resistors must be grounded. This grounding resistor (6b, 7
b, 8b) and FET switch (13, 14, 15) connected in series, and
By turning on / off the ET switch (13, 14, 15), T
-Type resistance attenuator circuit configuration is connected and disconnected to prevent leakage to the ground side.

In FIG. 3, the FET switch (2) is turned on,
If the FET switch (13) is turned off, the signal flows through the FET switch (2) and the T-type resistance attenuator cannot be grounded.
Signals leaking to ground through the mold resistance attenuator are blocked.
Conversely, if the FET switch (2) is turned off and the FET switch (13) is turned on, the signal flows to the T-type resistance attenuator side. Here, the FET switch (13) may be connected either before or after the resistor (6b). Also, the FET switch on the T-type resistance attenuator side
The feature (13) is that the gate width may be shorter than that of the FET switch (2). This is because even if the ON resistance value of the FET switch (13) is large, it can be corrected by the resistor (6b).

FIG. 4 shows an example using a pie resistance attenuator. Similar to the second embodiment of FIG. 3, the FET switch (13, 1) is connected to the grounded resistors (6b, 7b, 8b) of the pie resistance attenuator.
4,15) are connected in series. Turn on the FET switch (2),
If the FET switch (13) is turned off, the signal flows through the FET switch (2), and conversely, the FET switch (2) is turned off and the FET is turned on.
When the switch (13) is turned on, the signal flows to the pie resistance attenuator side.

[0016]

According to the present invention, since the total number of switches and the number of signal passing switches can be made smaller than in the conventional case, a step attenuator can be realized with a smaller chip area and a smaller insertion loss, and high performance can be achieved. It is also advantageous from the standpoint of making ICs.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a step attenuator according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional step attenuator.

FIG. 3 is a circuit diagram of a step attenuator according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a step attenuator circuit according to a third embodiment of the present invention.

[Explanation of symbols]

1 ... Input terminal, 2-4, 13-15 ... FET switch, 5 ...
Output terminal, 6-8 ... Attenuator, 9 ... Resistor, 10-12, 16-1
8 ... Control terminal.

Claims (2)

[Claims] 1. An input / output switch for passing / blocking an input signal to / from an output terminal is provided between an input terminal and an output terminal, and an attenuator having an arbitrary amount of attenuation is installed in parallel with the switch.
A step attenuator capable of obtaining two kinds of signal levels of a signal passing through the switch side and a signal passing through the attenuator side by turning on / off the switch. 2. The step attenuator according to claim 1, wherein
A step attenuator characterized in that a connecting / disconnecting switch is provided in series with a grounded resistor of an attenuator composed of resistors, and an input / output switch and a disconnecting switch are turned on / off complementarily.