Tunable voltage controlled oscillators
A tunable voltage oscillator expands a voltage oscillator's tuning range and compensate for any frequency spread present in the voltage oscillator. The tunable voltage oscillator multiplies a frequency of a periodic signal generated by the voltage oscillator by a fractional number. This fractional number is determined by a desired frequency range and an actual frequency range of the voltage oscillator. As such, the frequency range of the output periodic signal is tuned into the desired range. The voltage oscillator can include a programmable inductor of which the inductance can be adjusted thereby to expand the frequency range by increasing the quality factor in the low frequency range.
1. A tunable voltage oscillator comprising:
a voltage oscillator configured to generate a first periodic signal according to a control voltage, the first periodic signal having a first frequency in a first frequency range defined by a first minimum value and a first maximum value;
a fractional multiplier configured to receive the first periodic signal and to generate a second periodic signal by multiplying a first frequency of the first periodic signal by a fractional number, the second periodic signal having a second frequency in a second frequency range defined by a second minimum value and a second maximum value, the fractional number being the second minimum value divided by the first minimum value or the second maximum value divided by the first maximum value; and
a multiplexer configured to combine the first periodic signal and the second periodic signal to generate an output periodic signal.
2. The tunable voltage oscillator of claim 1 , wherein the first frequency range is determined at a process corner of the voltage oscillator, the process corner having a highest value of a minimum programmed frequency and a lowest value of a maximum programmed frequency among all process corners of the voltage oscillator.
3. The tunable voltage oscillator of claim 1 , wherein the fractional multiplier includes at least one multiplier and at least one divider that are connected in series, the at least one multiplier and at least one divider configured to multiply the first frequency of the first periodic signal by the fractional number.
4. The tunable voltage oscillator of claim 1 , wherein the voltage oscillator comprises a current source configured to provide a current, a first inductor, a second inductor, a capacitor bank, a first transistor, and a second transistor, the current source is coupled to a first terminal of the first inductor and a first terminal of the second inductor, a first terminal of the capacitor bank coupled to a second terminal of the first inductor that is further coupled to a first output terminal, a second terminal of the capacitor bank coupled to a second terminal of the second inductor that is further coupled to a second output terminal, the first output terminal coupled to a drain of the first transistor and a gate of the second transistor, the second output terminal coupled to a drain of the second transistor and a gate of the first transistor, and a source of the first transistor coupled to a source of the second transistor that is further coupled to the ground, wherein the capacitor bank is configured to oscillate with the first inductor and the second inductor to output the first periodic signal from the first output terminal and the second output terminal.
5. The tunable voltage oscillator of claim 4 , wherein the capacitor bank comprises a first capacitor and a second capacitor coupled in series, the first output terminal coupled to a first terminal of the first capacitor, the second output terminal coupled to a first terminal of the second capacitor, and a second terminal of the first capacitor that is connected to a second terminal of the second capacitor.
6. The tunable voltage oscillator of claim 4 , wherein the voltage oscillator further comprises a first varactor and a second varactor coupled in series, the first output terminal coupled to a first terminal of the first varactor, the second output terminal coupled to a first terminal of the second varactor, the second terminal of the first varactor coupled to the second terminal of the second varactor and configured to receive a voltage to adjust the first frequency of the first periodic signal.
7. The tunable voltage oscillator of claim 4 , wherein the at least one of the first inductor and the second inductor is a programmable inductor.