Tunable lowpass-highpass switching filter

• US 4,731,877 A
• Filed: 05/29/1986
• Issued: 03/15/1988
• Est. Priority Date: 05/31/1985
• Status: Expired due to Term

• Current Assignee: Samsung Electronics Company Limited and Pocons Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Electronics Company Limited and Pocons Company Limited (Samsung Electronics Co. Ltd.)
• Inventors: Moon, Fredrick H.
• Primary Examiner(s): Masinick, Michael A.
• Application Number:
  US06/869,385
• Time in Patent Office: 656 Days
• Field of Search: 455/131, 455/180, 455/188-191, 455/284, 455/307, 455/315, 455/339, 455/340, 333/103
• US Class Current: 455/340
• CPC Class Codes: H03H 7/01 Frequency selective two-port networks
• CPC Class Codes: H03H 7/1758 Series LC in shunt or branch path H03H7/1791 takes precedence
• CPC Class Codes: H03J 5/244 using electronic means
• CPC Class Codes: H04B 1/18 Input circuits, e.g. for coupling to an antenna or a transmission line coupling networks between antennas or lines and receivers independent of the nature of the receiver H03H
• CPC Class Codes: H04N 7/104 Switchers or splitters

Abstract

A filter is used for multichannel communication receiver, e, g, a CATV converter, which is electronically switched for a lowpass or highpass configuration by switching diodes, and the rejection bandwidth is further controlled by varactor diodes depending on the receiving channel frequency. This reduces the modulation distortions such as composite second and third order inter-modulation and cross-modulation by limiting the number of channels processed by the receiver.

Claims

1. A tunable and switchable filter for reducing intermodulation distortion levels in a multichannel communications receiver comprising:

an input terminal for receiving signals broadcast over a plurality of communication channels;

an output terminal;

first and second series connected capacitors coupled between said input terminal and said output terminal;

first and second series connected inductors coupled between said input terminal and said output terminal;

third and fourth series connected inductors, a third capacitor and a first variable capacitance diode connected in series between the common junction of said first and second series connected inductors and the common junction of said first and second capacitors;

first and second diodes for selectively shunting one of the common junction of said first and second capacitors and the common junction of said third and fourth inductors directly to reference ground potential, wherein said selective shunting establishes one of a lowpass and a highpass filter characteristic between said input terminal and said output terminal;

a third diode for selectively shunting said first and second inductors directly to reference ground potential for lowering the frequency of the trap in highpass filter mode.

2. A tunable and switchable filter for reducing intermodulation distortion levels in a multichannel communications receiver comprising;

an input terminal for receiving signals broadcast over a plurality of communications channels;

an output terminal;

at least two series connected capacitors coupled between said input terminal and said output terminal;

at least two series connected inductors coupled between said input terminal and said output terminal;

a pair of series connected inductors, a capacitor and a first variable capacitance diode coupled between the common junction of said two series connected capacitors coupled between said input terminal and said output terminal, and the common junction of said two series connected inductors coupled between said input terminal and said output terminal;

first and second switching means for selectively shunting one of the common junction of each pair of series connected capacitors coupled between the input terminal and the output terminal, and the common junction of each corresponding pair of inductors coupled between the input terminal and the output terminal, directly to reference ground potential, wherein said selective shunting establishes one of a lowpass and a highpass filter characteristic between said input terminal and said output terminal;

third switching means for selectively shunting the common junction of two series connected inductors coupled between said input terminal and said output terminal directly to reference ground potential for lowering the frequency of the trap in highpass filter mode.