Digital-analog frequency error signaling

The method of producing a bipolar error signal representing the analog of the error between a changeable frequency of an input signal and a set point frequency, wherein said input signal is a recurring squarewave A with the duration of each square pulse therein variable inversely according to changes in the frequency of the input signal, said method comprising

• a. generating a standard interval signal constituted by successive squarewaves B each of which begins substantially in synchronism with the start of each of said square pulses in said input signal, and each of which is of a predetermined time duration,
• b. utilizing said input and standard signal to
• b1. produce a first pulse whenever and so long as the standard signal is present annd the input signal is absent, and
• b2. produce a second pulse whenever and so long as the input signal is present and the standard signal is absent, and
• c. utilizing said first and second pulses to produce an output signal which varies in polarity and magnitude according to the sign and the size of the difference between the time durations of said first and second pulses.

In apparatus for producing an analog signal representing the error between a set point frequency and a variable frequency, the combination comprising:

• a. means for producing a first periodic signal A recurring at the variable frequency and having successive periods of existence which in time duration are inversely proportional to such frequency,
• b. means for producing a second periodic signal B having successive period of existence of predetermined constant duration, each period of existence beginning substantially in synchronism with the start of a period of said first signal,
• c. means for producing a first pulse whenever and so long as said first signal exists in the absence of said second signal,
• d. means for producing a second pulse whenever and so long as said second signal exists in the absence of said first signal,
• e. means responsive to said first and second pulses for producing an output signal which varies in polarity and magnitude according to the average of the diffference between the time durations of said first annd second pulses.

In apparatus for producing an analog signal representing the error betweeen a set point frequency and the variable frequency of a recurring event, the combination comprising:

• a. means for producing a first recurring squarewave signal having the frequency of said recurring event, with the time duration of each squarewave inversely proportional to such frequency,
• b. means responsive to said first signal for producing a second squarewave signal with the beginning of each squarewave therein substantially coincident in time with the beginning of each squarewave in the first signal, and with each squarewave therein having a predetermined, constant time duration,
• c. means for producing a first pulse during intervals when a second signal squarewave is present but a first signal squarewave is absent except for a predetermined delay period at the beginning of each such interval,
• d. means for producing a second pulse during intervals when a first signal squarewave is present but a second signal squarewave is absent except for a predetermined delay period at the beginning of each such interval, and
• e. means responsive to said first and second pulses for producing an output signal which varies in polarity and magnitude according to the time average of the difference between the time durations of the first and second pulses.

In a method of measuring off repeated precise time intervals T.sub.b, in response to each of successive stimulating input signals, which includes

• a. generating a recurring train of clock pulses at a precise frequency, such pulses forming a signal which periodically switches between 1 and 0 logic levels,
• b. gating said clock signals into a counter in response to each input signal until the counter has counted a predetermined number of its responses, said counter responding to wave front transitions of a predetermined direction (either 0 to 1 or 1 to 0) applied to its input,
• and wherein said method is characterized by the improvement of
• 1. coupling the gated clock pulses to said counter such that the first wave front of said predetermined direction appearing at the input of said counter when gating is initiated results from switching of the level in the clock pulse signal rather than from initiation of the gating action,
• whereby the time interval T.sub.b between the registration of the first count and the last count in said counter is always an integral multiple of the period of said clock pulses.

In a method of measuring off a precise time interval in response to a stimulating input signal, which includes:

• a. generating a recurring train of clock pulses at a precise frequency, such pulses forming a signal which periodically switches between 0 and 1 logic levels,
• b. opening a gate to couple said clock pulses into a counter in response to each input signal, said counter responding and registering a count in response to a wave front transition of a predetermined direction (either 0 to 1 or 1 to 0) at the output of said gate,
• c. terminating the gating in response to the counter having registered a predetermined number of counts,
• and wherein said method is characterized by the improvement of:
• coupling the gated clock pulses to said counter such that the first wave front of said predetermined direction, appearing at the output of said gate upon initiation of gating action, results from a switching of the level in the clock pulse signal,
• whereby the interval between the registration of the first and the last count in said counter is an integral multiple of the period of said clock pulses.

In a method off precise time intervals in response to successive stimulating input signals, which includes

• a. generating a recurring train of clock pulses at a precise frequency, such pulses forming a signal which periodically switches between 0 and 1 logic levels,
• b. initiating the enablement of a gate to couple said clock signals into a counter in response to each input signal, and continuing such gating until the counter has registered a predetermined number of counts,
• b1. said counter registering a count in response to a level transition in a predetermined direction (either 0 to 1 or 1 to 0) at the output of said gate,
• and said method being characterized in that
• 1. the step (b) of initiating the enablement of said gate is carried out to produce either no response or a level transition opposite to said predetermined direction if it occurs when said clock pulse signal exits at either a 1 or a 0 level.

In a system having

• a. a precision frequency source of clock pulses which form a signal periodically switching between 1 and 0 logic levels,
• b. a counter adapted to respond to and count wave fronts of a predetermined direction (0 to 1 or 1 to 0) applied to its input,
• c. gate means, enabled by each one of a succession of input signals which arrive with lower frequency and in random, non-synchronized relation to said clock pulses, for transmitting said clock pulses to the input of said counter,
• d. means responsive to the counter reaching a predetermined count state N.sub.c for disabling said gate means, and
• e. means for resetting said counter to a predetermined reset state N.sub.r prior to the next enablement of said gate means,
• whereby the time interval T.sub.b measured off between the start and the end of each counting cycle is approximately constant and determined by the frequency of said source and the difference (N.sub.c -- N.sub.r) between said predetermined count and reset states,
• the improvement comprising
• means responsive to each input signal for enabling said gate means at an instant such that the input to said counter next undergoes a wave front transition of said predetermined direction only as a consequence of a level switching in the clock pulse signal,
• whereby said time interval T.sub.b is precisely constant for all counter cycles and is always an integral multiple of the period of said clock pulses.

In a precise standard time interval generator having

• a. a precision frequency source of clock pulses which form a signal periodically switching between 1 and 0 logic levels,
• b. a counter adapted to respond to and count wave fronts of a predetermined direction (either 0 to 1 or 1 to 0) applied to its input,
• c. means including a gate for transmitting said clock pulse signal to the input of the counter, said gate being enabled or disabled by a 1 or 0 level in a control signal applied thereto,
• d. means responsive to the counter reaching a predetermined count for switching said control signal from a 1 to a 0 level and disabling said gate, and
• e. means responsive to an input signal, which may appear in random, non-synchronized relation to said clock pulses, for switching said control signal to a 1 level to enable said gate,
• the improvement characterized in that said means (c) includes means for causing the first signal transition of said predetermined direction at the input of said counter following enablement of said gate to result from a level switching transition in the clock pulse signal.

In a system for measuring off a precise time interval each time a stimulating input signal is received, such system having

• a. a precision frequency source of clock pulses which form a signal switching between 0 and 1 logic levels,
• b. a counter adapted to respond to a wave front of predetermined direction (either 0 to 1 or 1 to 0).
• c. gate means receiving as a primary input said clock pulses and having its output coupled to said counter,
• d. a bistate device coupled to said gate means to enable and disable the latter when in the set or reset state, respectively,
• e. means responsive to each of successive input signals, which are random and non-synchronized in relation to said clock pulses, for setting said bistate device, and
• f. means responsive to the counter reaching a predetermined count state for (i) resetting said bistate device, and (ii) resetting the counter to a predetermined reset state,
• the improvement comprising
• means for coupling the outpt of said gate means to the input of said counter such that the first wave front of said predetermined direction applied to the counter input following each enablement of said gate means is created in consequence of a level switching of the clock pulses signal.