GB1100634A - Frequency divider with variable digital ratio - Google Patents

Abstract

1,100,634. Electronic counters. INTERNATIONAL STANDARD ELECTRIC CORPORATION. 7 May, 1965 [14 May, 1964], No. 19344/65. Heading G4A. Apparatus for dividing a fixed frequency by a large number comprises a programme unit which is stepped as components of said number are attained, the completion of the programme issuing a pulse of the desired lower frequency. The units, decimals and hundreds of the divisor are set up on dials U, D, C so as to mark matrices in a combined marking device 5. These matrices are connected to the outputs of a binary counter 2 so as to represent u + a, 10d + b, 100c - e/5 and p = e - a - b, where a and b are pulses added to the units and tens programme cycles, e is a number deducted from the total of 5 hundreds programme cycles, and p is a make-up number to correct for the adjustments. At the beginning of a programme counters 2 and 4 are at zero, flip-flop 15 is at 0 and gate 12 is open. Input pulses at 7 advance counter 2 until it attains the value u + a when AND gate 24U opens to pulse AND gate 26U, the other input of which is already marked by AND gate 28U because of the zero setting of programme counter 4. Flip-flop 15 is therefore switched to close gate 12 and open gate 13 to one input pulse from 7 whereby counter 2 is returned to zero. At the same time 15 pulses lead 18 to step the programme counter 4. Restoration of counter 2 acts through inverter 7 and gate 19 to restore flip-flop 15 so that the tens programme begins. The tens programme is followed by the make-up programme and five hundreds programmes, AND gate 26C operating five times under the control of 28C and 29 while programme counter steps from 3 through 7 to 0. A rectangular waveform is obtained from the last stage of the programme counter 4. By suitable arrangement of the controlling matrices (Fig. 4, not shown) the output waveform can change polarity at exactly or substantially half-way, according to whether the divider is even or odd.