Band-switchable, low-noise voltage controlled oscillator (VCO) for use with low-q resonator elements

A variable frequency oscillator comprising:

• a first load coupled between a first supply voltage terminal for receiving a first supply voltage and a first differential output terminal;
• a second load coupled between the first supply voltage terminal and a second differential output terminal;
• a first pair of cross-coupled transistors having a first collector node, a second collector node, and a common emitter node, the first and second collector nodes forming a differential output for providing a differential oscillator output signal;
• a first delay element connected between the first and second collector nodes of the first pair of cross-coupled transistors, the first delay element having a first delay;
• a second pair of cross-coupled transistors having a first collector node coupled to the first differential output terminal, a second collector node coupled to the second differential output terminal, and a common emitter node;
• a second delay element connected between the first collector nodes of the first and second pairs of cross-coupled transistors, the second delay element having a second delay;
• a third delay element connected between the second collector nodes of the first and second pairs of cross-coupled transistors, the third delay element having a third delay;
• and
• a switchable current source having a first output connected to the common emitter node of the first pair of cross-coupled transistors, a second output connected to the common emitter node of the second pair of cross-coupled transistors, and a control input for receiving a control signal, the switchable current source providing a current to the second pair of cross-coupled transistors responsive to a first state of the control signal to turn on the first pair of cross-coupled transistors and a current to the second pair of cross-coupled transistors responsive to a second state of the control signal to turn on the second pair of cross-coupled transistors,
• wherein the oscillator output signal has a first frequency of oscillation that is inversely proportional to the first delay when the first pair of cross-coupled transistors are turned on and a second frequency of oscillation inversely proportional to the sum of the first, second and third delays when the second pair of cross-coupled transistors are turned on.

A variable frequency oscillator comprising:

• a load coupled between a first supply voltage terminal and a first output terminal;
• a first transistor having a collector, an emitter coupled to an AC ground, and a base coupled to the first output terminal for providing an oscillator output signal of a first polarity;
• a current source coupled to the emitter of the first transistor;
• means for biasing the first transistor;
• a second transistor having a collector, an emitter connected to the collector of the first transistor to form a second output terminal for providing an oscillator output signal of a second polarity, the second polarity being opposite the first polarity, the second transistor having a base forming a control terminal for receiving a first control signal, the second transistor being turned on responsive to the first control signal;
• a first delay element connected between the first output terminal and the collector of the second transistor, the first delay element having a first delay,
• wherein the oscillator output signal has a frequency of oscillation that is inversely proportional to the first delay when the second transistor is turned on by the first control signal.

An oscillator comprising:

• a first transistor having a base, a collector, and an emitter;
• a second transistor having a base, a collector, and an emitter;
• a current source coupled to the emitters of the first and second transistors;
• a first load coupled between a first supply voltage terminal and the base of the first transistor to form a first output terminal for providing a first differential oscillator output signal;
• a second load coupled between the first supply voltage terminal and the base of the second transistor to form a second output terminal for providing a second differential oscillator output signal;
• a first delay element connected between the first output terminal and the collector of the second transistor, the first delay element having a first delay;
• and
• a second delay element connected between the second output terminal and the collector of the first transistor, the second delay element having a second delay equal to the first delay.

A method of generating a plurality of oscillation frequencies comprising the steps of:

• providing an inverter;
• providing a plurality of delay elements, each having a respective delay;
• connecting each of the delay elements in series from a first delay element to a last delay element;
• providing a plurality of switches, each switch associated with one of the delay elements;
• closing one of the switches and opening all of the other of the switches thereby creating a loop that includes the inverter and all of the delays from the first delay to the delay associated with the closed switch;
• and
• providing an oscillator signal that has a frequency of oscillation inversely proportional to twice the sum of the delays of all the delay elements in the loop.