US 7,030,688 B2 · Low-pass filter for a PLL, phase-locked loop and semiconductor integrated circuit

Abstract

The invention provides a low-pass filter suitably used as a loop filter for a PLL or a DLL that has a filtering characteristic equivalent to that of a conventional one and can be realized in a smaller circuit area. The low-pass filter includes first filtering means (31) for accepting, as an input, an input signal to the low-pass filter and outputting a first voltage; a circuit element (311) included in the first filtering means (31) for allowing a first current to flow in accordance with the first voltage; current generating means (32) for generating a second current at a given rate to the first current; second filtering means (33) for accepting, as an input, the second current and outputting a second voltage; and adding means (34) for adding the first voltage and the second voltage and outputting an output signal of the low-pass filter, in which the second current is set to be smaller than the first current.

Claims43

Dependent claims

A low-pass filter comprising:

first filtering means that receives an input signal to said low-pass filter and outputs a first voltage;
a circuit element included in said first filtering means for generating a first current in accordance with said first voltage;
current generating means for generating a second current at a given rate to said first current;
second filtering means that receives said second current and outputs a second voltage;
and
adding means for adding said first voltage and said second voltage and outputting an output signal of said low-pass filter,
wherein said given rate is a positive number smaller than 1.

4 more elements

A feedback system for feeding back an output clock, generated in accordance with an input clock, to make said output clock attain a desired characteristic, comprising:

a charge pump circuit for generating a charge current in accordance with a phase difference between said input clock and a clock resulting from the feedback;
a loop filter for filtering said charge current;
and
output clock generating means for generating said output clock in accordance with an output signal from said loop filter,
wherein said loop filter includes:
first filtering means for filtering said charge current and outputting a first voltage;
a circuit element included in said first filtering means for generating a first current in accordance with said first voltage;
current generating means for generating a second current at a given rate to said first current;
second filtering means for filtering said second current and outputting a second voltage;
and
adding means for adding said first voltage and said second voltage and outputting said output signal, and
said given rate is a positive number smaller than 1.

9 more elements

Dependencies are inferred from the claim text.

Facts

Application

10/500,875Filed 22 May 2003

Priority

JP 2002-14812922 May 2002

Published

US 2005/0077955 A114 Apr 2005

Granted

18 Apr 2006

Term ends

Not estimatedThe source records don’t support an estimate.

Classification6 codes

H03L 7/0891
The phase or frequency detector generating up-down pulses: the up-down pulses controlling source and sink current generators, e.g. a charge pump
H03L 7/0816
And where no voltage or current controlled oscillator is used: the controlled phase shifter and the frequency- or phase-detection arrangement…
H03L 7/0893
The up-down pulses controlling source and sink current generators, e.g. a charge pump: the up-down pulses controlling at least two source current…
H03L 7/0896
Details of the current generators: the current generators being controlled by differential up-down pulses

Low-pass filter for a PLL, phase-locked loop and semiconductor integrated circuit

Life of this patent

Low-pass filter for a PLL, phase-locked loop and semiconductor integrated circuit

Life of this patent

Abstract

Claims43