NOISE CANCELLATION CIRCUIT

• US 3,715,488 A
• Filed: 04/01/1971
• Issued: 02/06/1973
• Est. Priority Date: 04/03/1970
• Status: Expired due to Term

• Current Assignee: Tadashi Takise, Takashi Okada
• Original Assignee: Tadashi Takise, Takashi Okada
• Inventors: Okada, Takashi, Takise, Tadashi
• Primary Examiner(s): Richardson, Robert L.
• Application Number:
  US05/130,084
• Time in Patent Office: 677 Days
• Field of Search: 178/7.3R,7.3S,7.3DC,7.5R,7.5S,7.5DC,DIG.12
• US Class Current: 348/534
• CPC Class Codes: H04N 5/213 Circuitry for suppressing or minimising impulsive noise for suppressing or minimising disturbance in image signal generation H04N23/81

Abstract

An amplifier circuit for stabilizing sync circuits and reducing noise voltage spikes that extend beyond sync signal level of a television signal. The television signal is applied through a rectifier and smoothing circuit to a differential amplifier, which includes a normally non-conductive switching element that forms part of a voltage divider for the television signal. The same signal, without rectification or smoothing, is also applied to the differential amplifier. Noise voltage peaks exceeding sync peaks cause the differential amplifier to make the switching element conduct and activate the voltage divider to divide the television signal in order to bring noise pulse peaks below the sync level.

Claims

1. A noise reduction and synchronization stabilization circuit comprising:

A. Circuit means having a common terminal, an input terminal and an output terminal, means connecting the input terminal to the output terminal to transmit therebetween a television signal including synchronizing pulses having a pre-determined polarity and noise pulses, and a first voltage dividing circuit for providing a first signal representative of said television signal but reduced in amplitude by a predetermined amount;

B. Unidirectionally conductive means connected to said first voltage dividing circuit to provide a rectified output signal;

C. A smoothing circuit connected to said first voltage dividing circuit for rectifying said first signal and smoothing out amplitude variations in said rectified first signal; and

D. A switching element including

2. a second input connected to said smoothing circuit to be energized by the output signal therefrom, said switching element being conductive during noise impulses that exceed the amplitude of said synchronizing pulses;

E. A second voltage dividing circuit connected in series with said switching element between said common terminal and said output terminal to reduce the amplitude of said television signal at said output terminal during said noise impulses so that the amplitude of the noise pulse is at a level below that of the synchronizing pulse.

3. The circuit of claim 1 in which said unidirectionally conductive means comprises first and second diodes connected in series between said first voltage dividing circuit and said first input of said switching element.

4. The circuit of claim 1 in which said unidirectionally conductive means comprises a transistor connected in an emitter follower circuit.

5. The circuit of claim 1 in which said circuit means connecting said input terminal to said output terminal comprises an emitter follower transistor amplifier, and said unidirectionally conductive means includes a diode connected to an output of said emitter follower.

6. The circuit of claim 5 in which said switching element comprises a second transistor and a third transistor, the emitters of said second and third transistors being connected together, and a common emitter load for said second and third transistors, said smoothing circuit being connected to the base of said third transistor;

and voltage level setting means connecting said output of said emitter follower transistor amplifier to the base of said second transistor.

7. The circuit of claim 6 in which said voltage level setting means comprises at least one diode.