Converting circuit for converting differential signal to single-ended signal

• US 7,868,697 B2
• Filed: 11/26/2008
• Issued: 01/11/2011
• Est. Priority Date: 03/28/2008
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Arai, Tomoyuki
• Primary Examiner(s): Mottola; Steven J
• Application Number:
  US12/324,102
• Publication Number:
  US 20090243730A1
• Time in Patent Office: 776 Days
• Field of Search: 330/301, 330/311
• US Class Current: 330/301
• CPC Class Codes: H03F 1/0205 in transistor amplifiers
• CPC Class Codes: H03F 1/223 with MOSFET's
• CPC Class Codes: H03F 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 3/193 with field-effect devices H03F3/195 takes precedence

Abstract

A converting circuit for converting differential signals to a single-ended signal. The converting circuit comprises a cascode amplifier comprising a first transistor and a second transistor, wherein the first transistor comprises a control terminal, a first terminal, and a second terminal, the control terminal to which one of the differential signals is input, the control terminal being electrically-grounded; and, the second transistor comprises a first terminal and a second terminal, the first terminal of the second transistor being connected to the first terminal, the second terminal of the second transistor from which output signal is outputted, a capacitor for adjusting the phase, the capacitor being connected to the second terminal; and a current source being connected to the second terminal.

Claims

1. A converting circuit for converting differential signals to a single-ended signal, the differential signals being input to the converting circuit and the single-ended signal being outputted from the converting circuit, comprising:

a first transistor that includes a first terminal, a second terminal, and a control terminal for receiving a biasing voltage and a first differential signal;

a second transistor that includes a first terminal for outputting the single-ended signal and a second terminal connected to the first terminal of the first transistor;

a first capacitor for adjusting the phase of the first differential signal, the capacitor being connected to the second terminal of the first transistor; and

a current source connected to the second terminal of the first transistor.

2. The converting circuit of claim 1, wherein the first capacitor is a variable capacitor.

3. The converting circuit of claim 1, wherein the current source is a third transistor comprising a control terminal connected to a second capacitor that is grounded.

4. The converting circuit of claim 1, wherein a bias point of the first differential signal is equal to a bias point of a second differential signal.

5. The converting circuit of claim 2, wherein the variable capacitor is controlled based on an oscillation signal frequency outputted from a synthesizer included in a wireless device, to which the converting circuit is applied.

6. The converting circuit of claim 1, wherein the first transistor and the second transistor form a cascode amplifier.