# US 5,705,954 A · Differential output type filter circuit

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- Number: US 5,705,954 A
- Document ID: US5705954A
- Status: Granted
- Kind: A
- Application number: 08/637,494
- Filed: 1996-04-25
- Granted: 1998-01-06
- Earliest claimed: 1995-04-25
- Assignees: NEC Corporation
- Inventors: Masami Ishiyama
- Web page: https://patentgrep.com/patent/US5705954A

## CPC

- H03H 11/1213: {using transistor amplifiers (H03H11/1204 takes precedence; parallel-T filters H03H11/1295)}
- H03H 11/04: Frequency selective two-port networks
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)

## Abstract

A differential output type filter circuit comprises, between its input terminal and differential output terminal, a reference voltage generator circuit which receives supply voltage Vcc and outputs a reference voltage, an SVR correction circuit which filters out the noise component superposed on said reference voltage, an n-order filter circuit which functions to filter out the noise of an input signal corresponding to the input of this applied signal, this n-order filter circuit being composed of a first-stage primary filter circuit 3 and an (n-1)-order filter circuit 4, and a post-amplifier circuit 5 which receives and differentially amplifies the output signal from the SVR correction circuit and output signal 105 from said n-order filter circuit. This configuration represents a so-called single-signal input type filter circuit, and features compactness and excellent SVR characteristics.

## Claims

### Claim 1

A differential output type filter circuit comprising:
an n-order filter circuit which is provided with an input signal and which outputs the input signal after reducing superposed noise;
a reference voltage generator circuit which receives a supply voltage and which creates and outputs a reference voltage;
a supply voltage rejection and correction circuit which receives said reference voltage and which outputs the reference voltage after reducing or removing superposed noise; and
a post-amplifier which applies differential amplification to the output signal from said n-order filter circuit relative to the reference voltage applied from said supply voltage rejection and correction circuit and which creates and outputs a differential signal.

### Claim 2 (depends on 1)

The filter circuit according to claim 1, comprising:
a primary filter circuit which is set up in such a manner that the frequency characteristics of said supply voltage rejection and correction circuit that correspond to the noise will approximate those of said n-order filter circuit in the neighborhood of a specific arbitrarily selected frequency.

### Claim 3 (depends on 1)

The filter circuit according to claim 1, wherein said n-order filter includes
a first-stage primary filter which outputs said input signal after reducing superposed noise; and
an (n-1) order filter circuit which delivers the output signal from said primary filter circuit after reducing superposed noise.

### Claim 4 (depends on 2)

The filter circuit according to claim 2, wherein said n-order filter includes
a first-stage primary filter which outputs said input signal after reducing superposed noise; and
an (n-1) order filter circuit which delivers the output signal from said primary filter circuit after reducing superposed noise.