Timing recovery through distortion monitoring in data transmission systems

Claim 2

A distortion monitor for received synchronous digital data having a nominal absolute magnitude comprising means establishing adjustable caliper levels symmetrically straddling said nominal magnitude, means comparing the magnitude of received data at synchronous instants with each of said caliper levels to produce first and second output signals indicating whether the magnitude of said data is above or below the respective levels, means combining said first and second signals to form a third signal indicating whether said data is outside or between said caliper levels collectively, and hence, whether distortion is increasing or decreasing, and means responsive to said third signal adjusting the spacing between said caliper levels in a direction tending to capture succeeding data magnitudes therebetween.

Claim 3

The distortion monitor of claim 1 in which said means controlling the spacing between caliper levels comprises an integrator having a variable output, a transfer switch directly controlled by said third signal to apply a potential of one or the other polarity to said integrator as said third signal is in one state or the other, a potential source of said nominal magnitude, and means respectively adding to and subtracting from said nominal magnitude the potential of the output of said integrator to establish said caliper levels.

Claim 4

The distortion monitor of claim 1 in which said means controlling the spacing between caliper levels comprises a first multistage reversible counter counting at said synchronous rate and having its counting direction determined by said third signal, a resistive ladder network having steps of proportionately weighted values, a second multistage reversible counter driven by said first counter, means connecting the several stages of said second counter to the steps of said ladder whereby the attenuation factor of said ladder is proportional to the count in said second counter, a potential source having an output of said nominal magnitude, means shunting said ladder across said potential source to form a ladder output proportional to the deviation of received data magnitudes from said nominal magnitude, and means respectively adding to and subtracting from the output of said potential source the output of said ladder to constitute the respective caliper levels.

Claim 5

In combination with a synchronous digital data transmission system, a distortion monitor for data signals received at a terminal of said system, said monitor producing an output proportional to the deviation of received data signals at synchronous sampling instants from a predetermined absolute magnitude, a wave source operating at the synchronous data rate to supply timing signals at said sampling instants, reversible phase-shifting means continuously incrementing the phase of the timing signals from said source, means differentiating the output of said distortion monitor to obtain a derivative signAl indicative according to polarity of whether distortion is increasing or decreasing, and means responsive to the polarity of said derivative signal which indicates increasing distortion reversing the direction of incrementation of said phase-shifting means.

Claim 6

In combination with a synchronous digital data transmission system, a distortion monitor for data signals received at a terminal of said system, said monitor producing an output proportional to the deviation of received data signals at synchronous sampling instants from a predetermined absolute magnitude, a wave source operating at the synchronous data rate to supply timing signals at said sampling instants, reversible phase-shifting means continuously incrementing the phase of the timing signals from said source, means differentiating the output of said distortion monitor to obtain a derivative signAl indicative according to polarity of whether distortion is increasing or decreasing, and means responsive to the polarity of said derivative signal which indicates increasing distortion reversing the direction of incrementation of said phase-shifting means.

Claim 7

The combination defined in claim 4 in which said reversing means comprises a flip-flop toggled at a fixed rate, means correlating the output of said flip-flop with the derivative signal from said differentiating means to determine the output state of said flip-flop, an integrator, potential sources of equal opposite polarity, a transfer switch controlled by the output state of said flip-flop connecting said potential sources in the alternative to said integrator, and means connecting said integrator to said phase-shifting means to control its direction of operation.

Claim 8

The combination defined in claim 4 in which said reversing means comprises a multistage reversible counter having a fixed counting rate for integrating the output of said distortion monitor, reversible resistive ladder network having steps of proportionately weighted values, means connecting the several stages of said counter to the steps of said ladder whereby the overall voltage transfer characteristic of said ladder is proportional to the count in said counter, a potential source having a stable reference output, and means connecting said ladder across said potential source to form a ladder output proportional to a phase to be imparted to said sampling wave; and said phase-shifting means comprises a voltage controlled oscillator, a phase comparator having an output proportional to the difference in the phases of the waves from said sampling wave source and said oscillator, means summing the outputs of said ladder and said phase comparator to form a control signal, and means responsive to said control signal adjusting said voltage controlled oscillator to yield an equilibrium value of phase shift relative to that of said sampling wave source proportional to the output of said ladder network.

Claim 9

The combination defined in claim 4 in which said reversing means comprises a flip-flop toggled at a fixed rate, means correlating the output of said flip-flop with the derivative signal from said differentiating means to form a direction control signal for said flip-flop, and means connecting said flip-flop to said phase-shifting means to determine its slewing direction.

Claim 10

In a receiver for synchronous digital data in a band-limited transmission system in which distortion occurs, the combination comprising means establishing a nominal received amplitude level, means generating a variable difference signal which when added to and subtracted from said nominal level provides caliper levels symmetrically bracketing said nominal level, means rectifying received signals to obtain their absolute values, means responsive to a comparison of rectified received signals with said caliper levels producing a control output indicative of whether said received signals lie within or outside said caliper levels, a timing-wave source at said synchronous rate, means jointly responsive to said timing wave and said control output incrementing said variable difference signal in an increasing or decreasing direction depending on whether said received signals fall outside or inside said caliper levels, an incrementally variable phase-shifter in series between said timing wave source and said incrementing means, and means responsive to an increase of said variable difference signal reversing the direction of incrementation of said phase-shifter.

Claim 11

In a receiver for synchronous digital data in a band-limited transmission system in which distortion occurs, the combination comprising means establishing a nominal received amplitude level, means generating a variable difference signal which when added to and subtracted from said nominal level provides caliper levels symmetrically bracketing said nominal level, means rectifying received signals to obtain their absolute values, means responsive to a comparison of rectified received signals with said caliper levels producing a control output indicative of whether said received signals lie within or outside said caliper levels, a timing-wave source at said synchronous rate, means jointly responsive to said timing wave and said control output incrementing said variable difference signal in an increasing or decreasing direction depending on whether said received signals fall outside or inside said caliper levels, an incrementally variable phase-shifter in series between said timing wave source and said incrementing means, and means responsive to an increase of said variable difference signal reversing the direction of incrementation of said phase-shifter.