NOISE SUPPRESSION FILTER

• US 3,755,750 A
• Filed: 03/30/1972
• Issued: 08/28/1973
• Est. Priority Date: 03/30/1972
• Status: Expired due to Term

• Current Assignee: Emory D. Heberling
• Original Assignee: Emory D. Heberling
• Inventors: Heberling, Emory D.
• Primary Examiner(s): Heyman, John S.
• Application Number:
  US05/239,544
• Time in Patent Office: 516 Days
• Field of Search: 328/167,171,150 307/229,237,235
• US Class Current: 327/558
• CPC Class Codes: H03H 11/0405 Non-linear filters
• CPC Class Codes: H04J 3/025 Filter arrangements H04J3/08 takes precedence; filters per se H03H7/00, H03H9/00

Abstract

A simple and inexpensive device for filtering undesirable high frequency noise from analog data outputs of a data processing system, which operates in two different modes and switches automatically from one to the other depending on the rate of change of data functions and on data transient amplitude with respect to full scale. If the input data is a dc level or a slowly varying dc function, the subject device operates as a low pass filter to attenuate noise in the output, and if a step or square wave function occurs in the data the filter is automatically removed until the transition is completed and then the device reverts back to the low pass filter mode of operation.

Claims

1. A noise suppression filter system which operates in two different modes for optimizing the transmission bandwidth of analog data, switching from one mode to the other, depending upon the rate of change of data functions and on data transient amplitude with respect to full-scale amplitude, comprising:

a. circuit input and output terminals;

b. a resistance-capacitance low pass filter network means;

c. an operational amplifier, the output of which is connected to its inverting input and to said circuit output terminal;

d. said resistance-capacitance filter network means being connected between said circuit input terminal and the noninverting input to said operational amplifier, said resistancecapacitance low-pass filter network means having a cut-off in the lower portion of the data range. e. a pair of oppositely poled diodes connected across the input resistor of said resistance-capacitance filter means;

f. said diodes conducting when either of step and high frequency voltage signals of amplitude greater than the conduction voltage of said diodes occur at said circuit input terminal, establishing a low resistance path across said low-pass filter network and effectively shunting said low-pass filter network to switch the filter system from a low-pass mode to a wideband mode;

g. said filter system operating for steady state and dc data at any level in the modulation range as well as for slowly varying functions;

h. said filter system automatically switching to wideband mode for step and high frequency input data which exceeds + OR - 5 percent of full-scale data, and remaining in Wideband mode only for either of the duration of transients and fast rate-ofchange input data which causes diode conduction in either polarity and then reverting to low-pass model immediately following a step transition.

2. A filter system as in claim 1 wherein said low-pass filter network rejects noise components superimposed on low frequency data by approximately 6 db/octave above the low-pass filter cut-off with noise components in the range of from 1 to 5 kHz being significantly attenuated.