The present invention is directed generally to signal detection circuits and in particular to a digital signal detection apparatus.
Many different methods have been used to recover a serial digital signal sent over long transmission lines where the transmission line causes a distortion of the signal. A long transmission line will cause a distortion of the digital signal when the transmission line's pulse response does not allow the signal transition to reach its final value between any two signal voltage transitions. This distortion changes the zero crossing relationships for the signal where zero is defined as the mean voltage between the voltage extremes or the average voltage for the received signal. If the zero crossing detector circuits are used to recover the received signal, the signal will have a timing jitter and some of the information can be lost or distored if some of the zero crossing are lost.
In addition many of the generated digital waveforms have overshoot of the signal and the reflections which are generated by signal interaction which contain high frequency components.
The state of the art of detection circuits is well represented and alleviated to some degree by the prior art apparatus and approaches which are contained in the following U.S. Patents:
U.S. Pat. No. 2,510,983 issued to Krause on June 13, 1950; PA1 U.S. Pat. No. 2,695,359 issued to Levy on Nov. 23, 1954; PA1 U.S. Pat. No. 2,956,153 issued to Farlow on Oct. 11, 1960; PA1 U.S. Pat. No. 3,076,145 issued to Copeland et al on Jan. 29, 1963; PA1 U.S. Pat. No. 3,296,581 issued to Warner on Jan. 3, 1967; PA1 U.S. Pat. No. 4,032,847 issued to Unkauf on June 28, 1977.
The Warner patent discloses a circuit for deriving amplitude information from a signal transmitted over a transmission line which makes use of the fluctuation of the time period between zero crossing in the carrier signal due to noise.
The Farlow patent discloses a video slicer circuit which provides a noise free video output signal in response to a video input signal, irrespective of relatively wide variations in the noise level of the latter.
The Copeland et al patent discloses a circuit for eliminating ground clutter or noise from a received radar signal which discriminates between input pulses of different pulse widths and amplitudes.
The Krause, Levy and Unkauf patents are general background references each of which discloses a radio receiver for recovering intelligible information or data from a received signal that has been distorted during transmission.
While all of the above cited patent references are generally concerned with radio signals and the detection of the data information thereon, they are not directed particularly to the recovery of serial digital signals that have been distorted by long transmission lines. The present invention is directed toward a digital detection apparatus which is intended to satisfy that need.