Clock Converter Circuit

This invention relates to frequency multiplying devices in general and more particularly to a tapped delay line with an exclusive OR tree connected thereto to generate a harmonic square wave type of output signal from a basic clock signal. Frequency multiplying circuits have been in use for a long time, but have lacked precision in the multiplied output where some pulses might be generated with a different width to resynchronize the output with input transitions as in TV deflection circuits wherein a free running multivibrator is triggered by a synchronizing signal. Another known frequency doubler uses a non-tapped delay line and a single exclusive OR type circuit to generate a double frequency square wave type signal. This frequency doubler cannot be extended to higher frequency multiples of the input clock frequency.

It is then, an object of this invention to provide a frequency multiplying device for square wave clock signals which will provide an output square wave which is an integral frequency multiple of an input clocking signal.

It is also an object of this invention to provide a clock signal generator which will provide an output signal which is an accurate integer multiple of three or more of an input clock signal.

A further object is to combine such a frequency multiplier for square waves with a frequency divider whereby any rational multiple of an input signal frequency can be generated.

Another object is the provision of a device which can be designed to produce an output signal whose frequency bears a rational number relationship with the frequency of an input signal.

Other objects and advantages will be apparent in the following description with appended drawings of a preferred embodiment of the invention.

FIG. 1 is a schematic diagram of an embodiment of the invention.

FIG. 2 is a time graph showing the sequence of a clock pulse through the structure of FIG. 1.

The structure of FIG. 1 can be used to generate an output clock signal at a frequency bearing an integral relationship to a fixed frequency input clock. The device receives a square wave clocking signal at a frequency C from an associated machine, for example, a data processor and will multiply and divide the signal to generate a frequency m/n C.

In FIG. 1, a clocking signal will be received at a terminal 10 and will operate a frequency divider 11 of any of the known types such as a binary or decimal counter or a counter which resets itself whenever it reaches a set count or the like. The counter output line 12 will then carry a square wave of a frequency C/n where n is an integer. This C/n square wave is then applied to a tapped delay line 14 having a time delay T of at least T = m-1/2m . n/C where m is another integer different from n. The delay line 14 is tapped to provide at least (m-1) output signals at multiples of a time delay of n/2mC, i.e., the input signal delayed n/2mC, 2n/2mC, 3n/2mC, etc.

These (m-1) output signals together with the input signal to the delay line are entered into a parity tree 15 which will supply a significant signal output on line 16 when an odd number of significant voltage signals are present at the parity tree inputs. The parity tree 15 is a conventional configuration of layers of exclusive OR circuits 18, 19, and 20. All of the inputs to parity tree 15 from the delay line 14 are inputs in any order to exclusive OR's 18 and 19 of a first row and the outputs of the first row are further combined in the exclusive OR's such as 20 of the second row. Other rows of exclusive OR's may be used as needed to generate a single output from all required inputs. A representative exclusive OR circuit may be found in the publication, "Manual of Logic Circuits," by Gerald A. Maley, published by Prentice-Hall, Inc., in 1970 and deposited in the Library of Congress under card number. Exclusive OR circuits may be found at pages 47, 48, 51-56, 161, 162, 163 and 166-169. An exclusive OR parity tree 15, which provides an output signal when an even number of inputs are energized, is also possible.

FIG. 2 is a representation of the operation of the circuit of FIG. 1 on a time basis. The m selected for the circuit is 6 which requires (m-1) or 5 delay line sections with each section having a delay time t of 1/6 of a half cycle of the input signal from divider 11. The successive lines are taken at integral multiples of this time interval. At time T.sub.O, it will be seen that the output of divider 11 has been up long enough to pass completely through delay line 14 and therefore the input and all taps are at an up voltage. The parity tree receives 6 inputs and its output is at a down level. At time T.sub.0 +t, the output of divider 11 is at a down level so the delay line input is also down and only the five taps supply an up level signal to parity tree 15 which will now have its output at an up level. At time T.sub.O +2t the down level input has passed the first tap and only four up voltage signals are received at the parity tree 15 and its output is again at a down level. It will be seen that this alteration of outputs will continue as the down level signal passes the taps of delay line 14 so the parity tree receives successively 3, 2, and 1 up level signals and at time T.sub.0 +6t, the down level signal has passed all inputs. Now, the output level of divider 11 changes and at time T.sub.O +7t the up level has passed into the delay line 14 and the parity tree is receiving one high level signal. For each time increment of t, another of the parity tree inputs will be changed to an up level to switch the tree output signal until at time T.sub.O +12t, the signal status is back to where it was at T.sub.O and one complete cycle has been outputted from divider 11. It will be seen that over this period, the output on line 16 has passed through six full alterations so that the frequency multiplication factor is 6. Other multiplication factors m may be used by providing that the delay line is to have a time delay of at least m-1/m . n/2C with m-1 taps spaced at a time delay of n/2mC apart.

The combination of a frequency multiplier for any integral multiplication factor with a dividing circuit having a desired division factor n will enable generation of an output clock frequency which is any desired rational fractional m/n multiple of the frequency of an input clock signal. Modifications of the above described embodiment for other multiplication factors will be obvious from the above description which is not to be taken as a limitation of the scope of the invention.