Variable attenuator

• US 6,720,850 B2
• Filed: 04/02/2002
• Issued: 04/13/2004
• Est. Priority Date: 04/10/2001
• Status: Expired due to Fees

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Sasabata, Akihiro, Nakao, Motoyasu
• Primary Examiner(s): Nguyen, Long
• Application Number:
  US10/114,391
• Publication Number:
  US 20020196098A1
• Time in Patent Office: 742 Days
• Field of Search: 333/103, 333/101, 333/258, 333/262, 333/263, 333/81.R, 327/308, 327/268, 327/283, 327/290, 327/427, 455/82, 455/83, 455/307, 455/289, 455/290
• US Class Current: 333/261
• CPC Class Codes: H03H 11/245 using field-effect transistor
• CPC Class Codes: H03K 17/687 the devices being field-effect transistors
• CPC Class Codes: H03K 17/6874 in a symmetrical configuration
• CPC Class Codes: H03K 17/693 Switching arrangements with several input- or output-terminals, e.g. multiplexers, distributors logic circuits H03K19/00; code converters H03M5/00, H03M7/00

Abstract

A resonance type SPST switch is formed by connecting an inductive element in series with the drain of an FET, and then by connecting a capacitive element in parallel with the series connection of the FET and the inductive element. A constant-voltage source for feeding a voltage Vs is connected to the source of the FET, and a variable-voltage generator for switching the FET between an on state and a state in the vicinity of pinchoff is connected to the gate of the FET. When the variable-voltage generator feeds a voltage Vα in the vicinity of a pinchoff voltage to the gate of the FET, the SPST switch is closed while the amount of attenuation between first and second terminals is variably set. The resulting variable attenuator is thus compact in size, allows a large amount of attenuation to be set, and involves low manufacturing costs.

Claims

1. A variable attenuator comprising:

a FET;

an inductive element connected to one of the source and the drain of the FET thereby forming a series connection of the inductive element and the FET;

a capacitive element connected in parallel with the series connection of the inductive element and the FET;

a first terminal and a second terminal respectively connected to both ends of the capacitive element;

an attenuation setting unit which variably sets an amount of attenuation to a signal flowing between the first terminal and the second terminal by varying a voltage difference between the gate of the FET and one of the source and drain; and

a constant potential connected to the gate of the FET, wherein the attenuation setting unit is a variable-voltage generator which is connected to the source or drain of the FET to variably set the source or drain voltage of the FET.

2. A switching element with variable attenuation comprising:

a first SPST switch comprising a first inductive element connected to one of the source and the drain of a first FET thereby forming a first series connection of the first inductive element and the first FET, a first capacitive element connected in parallel with the first series connection of the first inductive element and the first FET, a first terminal and a second terminal respectively connected to both ends of the first capacitive element, and an attenuation setting unit which variably sets an amount of attenuation to a signal flowing between the first terminal and the second terminal by varying a voltage difference between the gate of the first FET and one of the source and drain;

a second SPST switch comprising a second inductive element connected to one of the source and the drain of a second FET thereby forming a second series connection of the second inductive element and the second FET, a second capacitive element connected in parallel with the second series connection of the second inductive element and the second FET, a third terminal and a fourth terminal respectively connected to both ends of the second capacitive element, the third terminal being connected to the second terminal; and

a voltage generator coupled to the gate of the second FET, and supplying a selected one of two constant voltage levels to the gate of the second FET, whereby said attenuation setting unit controls the conductive state of the first SPST switch and the voltage generator controls the conductive state of the second SPST switch.

3. A switching element with variable attenuation comprising:

a first SPST switch comprising a first inductive element connected to one of the source and the drain of a first FET thereby forming a first series connection of the first inductive element and the first FET, a first capacitive element connected in parallel with the first series connection of the first inductive element and the first FET, a first terminal and a second terminal respectively connected to both ends of the first capacitive element, and an attenuation setting unit which variably sets an amount of attenuation to a signal flowing between the first terminal and the second terminal by varying a voltage difference between the gate of the first FET and one of the source and drain; and

a second FET having one of its drains and source coupled to one of the drain and source of the first FET, a potential difference between the gate of the second FET and its drain or source being determined by said attenuation setting unit, the attenuation setting unit controlling the conductive state of the first SPST switch and the second FET,

wherein the gates of said first and second FETs are coupled to a constant potential source and said attenuation setting unit is a variable voltage generator coupled to a common connection comprising at least one of a source and drain of each of the first and second FETs.

4. The switching element of claim 3, wherein the gates of said first and second FETs are connected to ground potential.

5. A switching element with variable attenuation comprising:

a first SPST switch comprising a first inductive element connected to one of the source and the drain of a first FET thereby forming a first series connection of the first inductive element and the first FET, a first capacitive element connected in parallel with the first series connection of the first inductive element and the first FET, a first terminal and a second terminal respectively connected to both ends of the first capacitive element, and an attenuation setting unit which variably sets an amount of attenuation to a signal flowing between the first terminal and the second terminal by varying a voltage difference between the gate of the fist FET and one of the source and drain; and

a second FET having one of its drains and source coupled to one of the drain and source of the first FET, a potential difference between the gate of the second FET and its drain or source being determined by said attenuation setting unit, the attenuation setting unit controlling the conductive state of the first SPST switch and the second FET,

wherein said switching element has three terminals, a first terminal comprising a common connection comprising at least one of a source and drain of each of the first and second FETS, a second terminal comprising a common connection of said first capacitive element and said first inductive element and a third terminal comprising one of the source and drain of the second FET not connected to the common connection of said two FETS, and

wherein one of said second and third terminals is connected to a constant potential source.