Voltage controlled oscillator (VCO) employing nested oscillating loops

• US 4,105,950 A
• Filed: 09/12/1977
• Issued: 08/08/1978
• Est. Priority Date: 09/13/1976
• Status: Expired due to Term

• Current Assignee: RCA Corporation
• Original Assignee: RCA Corporation
• Inventors: Dingwall, Andrew G. F.
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US05/832,285
• Time in Patent Office: 330 Days
• Field of Search: 331/57, 331/108 B, 331/108 C, 331/108 D, 331/111, 331/113 R, 331/135, 331/143, 331/177 R
• US Class Current: 331/57
• CPC Class Codes: H03K 3/0315 Ring oscillators
• CPC Class Codes: H03K 7/06 Frequency or rate modulation, i.e. PFM or PRM

Abstract

The VCO is comprised of first and second "nested" oscillating loops. The first loop includes M cascaded inverters interconnected to normally oscillate at a given fixed frequency. The second loop includes N cascaded inverters where the input of the first of the N inverters is connected to the output of one of the M inverters and where the output of the Nth inverter is coupled to the output of a different one of the M inverters, whereby at least one of the M inverters is common to the two loops, and where M and N are integers. A control voltage is coupled to at least one of the N inverters to vary its conductivity and cause the frequency of oscillation of the two loops to change.

Claims

1. A voltage controlled oscillator comprising:

first and second terminals;

an input terminal adapted to receive a control voltage;

R, s and F cascaded inverters, where R, S and F are integers;

means connecting said R inverters and said S inverters in parallel between said first and second terminals;

said R and S inverters being connected in a direction to produce an output at said second terminal in response to an input at said first terminal;

means connecting said F inverters between said second and said first terminals in a direction to produce an output at said first terminal in response to an input at said second terminal;

said R and F inverters forming a loop when said control voltage is below a given level, which normally oscillates at a given frequency; and

means receptive to said control voltage being coupled to at least one of said S inverters for varying its conductivity and output current in response to said control voltage being above said given level and, in turn, varying the frequency of oscillation of said loop and said oscillator.

2. The combination as claimed in claim 1 wherein said means connecting said R inverters includes a resistor connected between the output of the Rth of said R inverters and said second terminal;

and wherein a capacitance greater in value than any stray capacitance associated with said R, S and F inverters is connected between said second terminal and a point of fixed operating potential.

3. The combination as claimed in claim 2 wherein R and S are each equal to 1 and F is equal to 2.

4. The combination as claimed in claim 1 wherein R, S and F are each equal to 1;

wherein said means connecting said F inverters between said second and first terminals includes a capacitor connected between the output of said F inverter and said first terminal; and

wherein said means connecting said R and S inverters in parallel includes means direct current connecting the inputs of said R and S inverters via negligible impedance means to said first terminal and resistive means connecting the output of one of said R and S inverters to said second terminal.

5. A voltage controlled oscillator comprising:

M inverters connected in cascade, and N inverters connected in cascade;

where M and N are integers;

means connecting the output of the Mth of said M inverters to the input of the first one of said M inverters for forming a loop normally oscillating at a predetermined frequency;

means connecting the input of the first of said N inverters to the output of one of said M inverters, and means connecting the output of the Nth of said N inverters to the output of a different one of said M inverters for forming a second loop; and

means responsive to an input control voltage connected to at least one of said N inverters for altering its conductivity in response to said control voltage and thereby altering said predetermined frequency of oscillation.

6. In combination with a first, voltage controlled oscillator, loop comprised of N cascaded inverters;

were N is an odd number equal to or greater than 1, and where the output of the Nth inverter is fed back to the input of the first inverter and where a control input voltage controls the voltage and current applied to at least one of the inverters of the first loop for controlling its frequency of oscillation, the improvement comprising;

R cascaded inverters;

means connecting the input of the first of said R inverters to the output of one of said N inverters; and

means including a reactive network connected between the output of the Rth of said R inverters and the output of a different one of said N inverters for forming a second oscillating loop and said reactive network being selected to cause said second loop to normally oscillate at a predetermined frequency when said control input voltage is below a given value.