US2446821A

US2446821A - Resistance-capacitance tuned oscillator

Info

Publication number: US2446821A
Application number: US570678A
Authority: US
Inventors: Gassel William; Gritz Henry
Original assignee: Philco Ford Corp
Current assignee: Space Systems Loral LLC
Priority date: 1944-12-30
Filing date: 1944-12-30
Publication date: 1948-08-10
Anticipated expiration: 1965-08-10

Description

Aug. 10, 1948. w. GAssEL ETAL RESISTANCE-CAPACITANCE TUNED OSCILLATOR Filed Dec. 30, 1944 Patented Aug. l0, 1948 RESISTANCE OAPACITANOE TUNED OSCILLATOR William Gassel, Philadelphia, Pa., and Henry Gritz, Iuka, Miss., assignors to Philco Corporation, Philadelphia, Pa., a, corporation of Penn- Sylvania Application December 30, 1944, Serial No. 570,678

2 Claims. .l Y

The invention relates to oscillation generators and more particularly to improvements in resistance-capacitance tuned oscillators.

As is well known, the tuning range for any one frequency band of a conventional resistance-capacitance tuned oscillator has a maximum to minimum frequency ratio of approximately tento-one. In order to generate oscillations over a wide frequency range, such as obtains from a practical wide range audio oscillator of this type, it is, at present, common practice to provide the oscillator with a suicient number of frequency bands to cover the desired frequency span. To this end, there is usually included in the frequency-determining network of the oscillator several sets of resistors, together with a switching means for connecting a particular set of resistors in the network circuit for each frequency band.

It is evident that certain advantages procure from an oscillator whose frequency may be varied in a continuous and smooth manner over a Wide range by one tuning control, rather than in a step-like fashion resulting from a plurality of frequency bands with the involved switching mechanism.

It is, therefore, the principal object of this invention to provide an improved resistance-capacitance tuned oscillator capable of generating a wide range of frequencies on one frequency band.

Another object of the present invention is to provide a novel and simple means whereby the usual tuning control of a resistance-capacitance tuned oscillator may vary the oscillator frequency over a Wide range.

Another object of the present invention is to provide a novel wide range audio oscillator.

A further object of t'his invention is to provide a novel frequency-determining network for a wide range resistance-capacitance tuned oscillator.

Other objects and advantages of the present invention will become apparent during the course of the following description taken in conjunction with accompanying drawing in which Fig 1 shows schematically one embodiment of the present invention applied to one of the more common types of conventional resistance-capacitance tuned oscillators; and

Fig. 2 shows a modification.

In Fig. 1 of the drawing, that portion of the circuit including the two-stage resistance-coupled amplifier represented by the block I' and the regenerative coupling network composed of resistors R1 and R2 and variable condensers C1 and C2 comprises one form of -a conventional resistance-capacitance tuned oscillator. Since the oscillator frequency depends upon the resistance of resistors R1 and R2 and the setting of variable condensers C1 and C2 the above network is often referred to as the frequency-determining network. In accordance with usual practice, the amplifier should preferably be provided with a suitable inverse feedback and amplitude control circuit to insure an oscillator output having good wave form. In practical oscillators of this type, the two resistors R1 and R2 are usually of the same value, and the two variable condensers C1 and C2 are similar and are ganged as illustrated in the drawing.

For each value of resistance for resistors R1 and R2, the frequency of the oscillator may be varied, by means of the tuning control attached to the ganged variable condensers C1 and C2, over a band whose frequency ratio is about 10 to 1.

In accordance with the present invention, the tuning control of a resistance-capacitance tuned oscillator is caused to Vary the oscillator frequency over a considerably increased frequency range. This is accomplished by means of the series-connected resistance-capacitance elements RaCa and R404, which are respectively connected in shunt relation with resistors R1 and R2. Each of the condensers C3 and C4 is of small capacity, and the resistance of resistors R3 and R4 is low in comparison to that of resistors R1 and R2. As the oscillator frequency is increased, the consequent decrease in the reactance of condensers Cz and C4 allows the resistors R3 and R4 to have more and more shunting effect upon the resistors R1 and R1 respectively, thereby lowering the effective resistance across these latter two resistors. Variation of both the capacity and the effective resistance of the frequency-determining network during oscillator tuning permits the tuning control to govern the oscillator frequency over a wide range of frequencies. By way of example, in an audio oscillator constructed in accordance with the embodiment of the invention illustrated in the drawing, a tuning range of 400 to 1 was attained. By selecting the proper element values for each resistance-capacitance mesh RaCa and Resistors R1 and R2 8.2 megohms each CondensersCi and C2 525 auf, each Resistor1R3 180,000 ohms Condenser C3 75 auf.

Resistor R4 220,000 ohms Condenser C4 60 [.Lpnf.

It should be noted that this invention provides*V a means of Calibrating the middle of the oscillator .scale without affecting the calibration of the high :or low ends of the scale. To this. end`,.a padder :condenser may be connected' across capacitor C. :as shown. It will be understood, of course, that :this element is optional. The calibration of the oscillator at the high end of the scale may, ofY

,course, be accomplished in the usual manner by :a padder condenser on variable capacitor C1. Am- Aplitude control may also be obtained inthe usual :manner by a padder condenser on variable capac- Although the invention has been described with reference tothe embodiment shown in Fig. 1 of the drawing, it is to be understood that the invention is not limited to the particular values given by way' of example, nor to the specific number and arrangement of the elements in the resistance-capa'citance networks, represented in the drawing by R303 and R4C4. For instance, the

values of resistance employed for resistors R1 and R2 may be such that the resistance of Rr is considerably different from that of R2.

Also, improvement in` the wave shape of the output voltage and the frequency response characteristic of the oscillator over its wide frequency range may be obtained by connecting a resistor 2 across capacitor C3, or by shunting a capacitor 3kacr0ss resistor R1, or, preferably, by employing both as shown in Fig. 2. Resistor 2 should be of sufcient resistance to have minimum effect upon the lowest frequency desired from the oscillator. Condenser 3 should be-of small -capacity in order that the higher frequency range of the oscillator will not be affected. The improved wave form is occasioned by the increase in degenerative feedback which may be applied to the amplifier l as a result of the increase in regenerative feedback obtained through these additional elements.

With resistor 2 and capacitor 3 in the regenerative feedback circuit there is also an increase in the amplitude of the output voltage in the lower middle portion of the frequency range thus compensating for a drop of voltage occurring at this part of the range when these elements are not used. Aside from these additional elements, Fig. 2 is similar to Fig. 1.

It will thus be apparent to those skilled in the art that the present invention is capable of various embodiments or modifications which may be resorted to without departing from its scope.

We claim:

1. In an oscillator circuit, an amplifier, a regenerative coupling network connected between the output and input of said amplier, said networkincluding a resistor and a variable capacitor connected in series between the output and input of said amplier, .and also including a second resistox. and a second variable capacitor connected in shunt relation across the input of said amplifier, and series-connected resistance and capacitance elements in shunt with each of said resistors. and adapted to vary the effective resistance of' said network in response to variation of the oscillator frequency, whereby to increase the frequency range of the oscillator.

2. In an oscillator circuit, an amplifier, a regenerative -coupling network connected between the output and input of said amplifier, said network comprising a rst branch including a resistor and a variable capacitor connected in series between the output and input of said amplifier and a second branch also including a resistor and a variable capacitor connected in shunt relation across the input of saidamplifier, and seriesconnected resistance and capacitance elements'in shunt with `at least one of said resistors and adapted to vary the effective resistance of one of said branches in response tothe variation of the oscillator frequency wherebyA to increase the frequency range of the oscillator.

" WILLIAM GASSEL.

HENRY GRII'Z.

REFERENCES CITED The following references are of recordv in ther ille ofthis patent:

UNITED STATES PATENTS Number Name Date 1,442,781 Nichols Jan. 16, 1923 2,024,489 Pal Dec. 17, 1935 2,268,872 Hewlett Jan. 6, 1942 2,356,248' Koren Aug. 22, 1944