US2861187A - Frequency divider - Google Patents

Description

Nov. 18, 1958 P. J. DE VITA FREQUENCY mvrmaav Filed sept. 5, A195e NVN OhmlT United States Patent FREQUENCY DIVIDER Philip Joseph De Vita, Chicago, Ill., assignor to Hammond Organ Company, ChicagoIll., a corporation of Delaware Application September 5, 1956, Serial No. 608,118 3 Claims. (Cl. Z50-36) 'cold cathode gas tubes together with input pulse amplifying triodes, and employing a single source of plate current supply. When the input frequency does not vary appreciably, the output signals of the several stages may be either or both waves of the substantially sine or square type, to facilitate the use of the frequency divider as a tone signal generator of an electrical musical instrument.

A further object is to provide an aperiodic frequency divider capable of embodiment in any desired number of cascaded stages, in which the components are relatively fewand in which the circuitry is relatively simple.

A further object is to provide a multi-stage aperiodic frequency divider which is stable and reliable in operation, despite variations of the frequency and amplitude f of the input pulses and despite variations in the'anode rA voltages.

Other objects will become apparent from the following description, reference being had to the accompanying' drawing which is a schematic wiring and block diagram of a frequency divider comprising seven stages.

The frequency divider comprises pulse input terminals 20 and 21, the latter terminal being shown as connected to a common ground. The terminal 20 is coupled to the grid 22 of a triode V-1A through a capacitor C26. A grid return resistor R28 connects the grid 22 to tap 35 of a grid bias source comprising an adjustable tap resistor R30 `and fixed resistor R32 connected in series between ground and a terminal 100 v. The adjustable tap resistor R30 has a bypass capacitor C34 connected in parallel therewith, and the junction between resistors R30 and R32 is connected to the cathode 36of the triode V-1A as well as to the eathodes of the corresponding triodes V1B to V-4A utilized in the succeeding stages. It will be noted also that the grid bias Voltage of all the triodes V-1B to V-4A is determined by the adjustment of tap 35 of resistor R30. The triodes are preferably twin triodes of the 12AX7 type.

Each stage of the divider includes a cold cathode gas tube 40 which has an anode 6 connected by resistor R42 to a conductor 44 leading to a -l-370 v. terminal of the power supply, and each of these tubes has a guide electrode 2 connected by conductor 46 with the plate 48 of the triode such as V-1A. A cathode electrode 1 in the tube 40 is connected to the common ground through a resistor R50 in parallel with a capacitor C51, which are connected in series with a parallel network comprising an inductance L52 and capacitor C54. The inductance L52 forms the primary of a transformer, the secondary L56 of which is connected between ground and an output terminal f/ZF. When the parallel network comprising inductance L52 and capacitor C54 is adjusted to be resonant at the frequency of pulses appearing on both cath- `next stage.

Patented Nov. 18, 1958 odes 1 and 3 of tube 40, the signal on terminal f/ZF with respect to ground, will be generally of sine wave shape, and in musical terms may be considered as resembling a ute-like tone. The cathode electrode 3 of tube 40 is connected to a terminal f/2C, upon which the signal will appear as a substantially square wave, representative in musical terms as a tone resembling that of the woodwind or clarinet family.

A cathode electrode 3 in the gas tube 40 is also connected to ground through resistor R60 which has a capacitor C62 connected in parallel therewith. The conductor 46 is connected to ground through a resistor R62 and in addition is connected to the gaseous tube anode current supply conductor 44 by a resistor R64. These two resistors constitute a voltage divider to provide a voltage of approximately +37 v. on the guide electrode 2 in the absence of a triggering pulse.

The electrode 3 is connected through a capacitor C66 (which 'corresponds to the capacitor C26 of the first stage) to the control grid 67 of the tube V-IB of the similar to the rst stage described in detail, and similar reference characters have been applied to corresponding v parts, it being understood that there may be differences in particular values of the components in the successive stages to facilitate operation at the different frequencies,

but most of the corresponding resistors willbe of the i same Value in each of the stages.

The output terminals of the several stages are designated as fractions of the input frequency f, followed by the letter R indicating flute, or the letter. C, indicating clarinet.

In operation, an input frequency is impressed kacross the terminalsv 20, 21, this input frequency being preferably in the form of positive pulses. If in the form 'of both positive and negative pulses, or other positive and negative wave form, only the positive portions will be effective to trigger the triode V-lA.

Assuming that in the initial state, there is an-ionized y path between electrodes 6 and 3 of tube 40, a positive pulse on the grid 22 of triode V-1A will cause the anode 48 which is normally at a positive potential with respect to ground to go negative-possibility more negative than the ground potential-and as a result there will be greater K potential difference between the anode 6 and guide electrode 2 than existed between the anode 6 and cathode electrode 3. which appears to the eye as la glow, willshift from the cathode electrode 3 to the guide electrode 2.

When the anode 48 is returned to its normal potential, determined by the voltage divider comprising R62.-

and R64 (R64 being approximately ten times as high in Value as R62 so that the voltage on conductor 46 is approximately one-tenth the B-jvoltage of 370, namely, 3 about +37 v.), the fact that cathode electrode 1 is at somewhat lower potential causes the ionization to shift from guide electrode 2 to cathode electrode 1, and the tube continues to operate in this condition until a second positive pulseY signal is supplied on the inputterminals 20, 21. Upon the second impulse, the ow pathl i' shifts from the cathode electrode 1 to the guide electrode 2 temporarily, and thereafter, upon cessation of the pulse impulse, the flow path shifts to cathode electrode 3. This is because the cathode electrode 1 was maintained at a higher potential due to the charge temporarily retained in capacitor C51, whereas at the same time the cathode electrode 3 will have been reduced to ground potential due to the discharge of capacitor C62 through resistor R60.

Upon reception of a third input pulse, the operation will be repeated, so that the two cathodes and the guide transfer current between anode 6 in the order of elec- This stage and the succeeding stages are Thus, the ionized path of current flow, f

3 trodes 3, 2, 1, 2, 3, 2, 1, etc., with the result that the input frequency is divided by a factor of 2 with respectl to the frequency of the pulses present on either electrodes 2 or 3.

The signal appearing on the cathode` electrode A3` is differentiated by virtuev of the capacitor C66 and the resistancel R28 associated with the-tube V-1B so that the signal for triggering the next stage is in the formof spikes with alternate positive and negative peaks, which is desirable for accurate, stable operation of the second stage:

It is desirable for best results to keep the potential of guide electrode 2 and anode 48 at a value above ground potential so that the guide electrode 2 will fire substantially near the peak of the negative pulse potential appearing on the anode 43. In other words, the guide electrode 2 of gaseous tube 40 is fired to shift the ionic current path and the current flow from either electrode 1 or electrode 3 substantially near this negative peak rather than at the initiation of or shortly following the initiation of the negative pulse on anode 48, which, if it occurred at the broader base portion of the negative pulse would of course result in signal wave shape which would be less like the ideal square wave shape desired at the signal output terminal f/ZC.

In view also of the fact that the guide electrode 2 and anode 48 are normally maintained at a voltage above ground potential, variations in the amplitude of input pulses and variations in the anode current supply voltage are less subject to influence the operation of the circuit, because, as the voltage on the conductor 44 drops, there is a corresponding drop in the positive bias potential on thefguide electrode 2, and thus the amplitude of the negative pulse required to transfer the current path to the guide electrode 2 of tube 40 may be of correspondingly lower value.

In the particular exemplary form of the invention, there are seven stages of frequency dividers so that, for example, if the apparatus is to be used in a musical tone generating system the input frequency impressed across the terminals 20, 21 may be 14,080 C. P. S. This input frequency may be derived from a suitable oscillator, the output of which may also be used to supply a tone frequency signal. Then the successive stages of the frequency divider apparatus will provide frequencies of 7040, 3520, 1760, 880, 440, and 220, which are musically useful. In another way in which the invention may be utilized, the input frequency will be provided by a variable frequency oscillator which may be tuned in any suitable manner to high harmonics of the semitones of 'a musical scale. Such instrument in which this arrangement would be employed would be of the melody type, and suitable switching means would be provided which would determine the particular stage or stages from which the output signal or signals would be derived. Such switching means are well known in the art.

In other forms in which the invention may be utilized, twelve frequency dividers and their corresponding driving oscillators, such as the one shown in this application,

would be employed respectively tuned to provide the 50 twelve semitone intervals for each of the five or six octaves in the register of an organ type instrument. In either form of utilization of the invention, the custom- 4 ary filter, formant, octave coupler, and control circuits, as desired, may be used.

The apparatus of the invention may produce either or both output signals of the substantially sine or square wave type which, in accordance with the known methods, may be modified to produce a large variety of tone qualities.

Iclaim:

1. In a frequency divider for dividing successively by the factor of two, the combination of a plurality of similar cascaded stages, each stage comprising a gaseous cold cathode tube having an anode, a pair of cathodes, and a guide electrode; an input signal amplifier having an anode the potential of which drops when a positive input pulse is supplied to the amplifier; a connection between the anode of the amplifier and the guide electrode; common means for supplying operating potentials to the anode of the cold cathode gaseous tube and the anode of the amplifier; meshes each comprising a capacitor in parallel with a non-capacitative impedance connected respectively between the gas tube cathodes and a point of fixed potential; means coupled to one of the gas tube cathodes to derive an output signal therefrom; means coupled to the other of the gas tube cathodes to supply a triggering signal to the amplifier of the next stage, in which there is included a transformer in the means coupled to one of the gas tube cathodes to derive an output signal therefrom, the transformer having primary and secondary windings; in which the mesh connected between one of the gas tube triodes and the point of fixed potential has as its non-capacitative impedance the primary winding of the transformer; and in which means are provided to derive a substantially sine wave output signal from the secondary'of the transformer.

2. The combination set forth in claim 1 in which means are provided to derive a substantially rectangular output signal wave from the other of the cathodes of the gas tube.

3. In a multi-stage cascaded frequency divider, in which each stage comprises a gas tube circuit responsive to alternate pulses supplied thereto, and in which there is included in each stage a non-gaseous electron discharge device for supplying pulses to the gaseous alternate pulse responsive means, the non-gaseous electron discharge device for the first stage being connected to an external source of pulses, the non-gaseous electron discharge device for the subsequent stages being connected to receive, sharpen, and amplify pulse signals derived from the gas tube of the preceding stage to amplify the latter, and connections from the non-gaseous device to supply controlling pulses to the gaseous tube of the following stage, whereby the output of each gaseous alternate pulse responsive circuit is amplified to provide a pulse of sufiicient amplitude reliably to trigger the following alternate pulse responsive gaseous tube circuit.

References Cited in the file of this patent UNITED STATES PATENTS 2,415,654 Place Feb. l1, 1947 2,593,375 Williams et al Apr. 15, 1952 2,780,751 Ridler Feb. 5, 1957

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