Patent Application
20180226921
The present invention relates to techniques for extending the tuning range of a voltage-controlled oscillator (VCO) using parasitic capacitance of semiconductor devices in the VCO circuit.
Modern phase-locked loops (PLLs) used for communications need to cover wide frequency ranges while maintaining phase noise performance. Enlarging the tuning range using conventional techniques typically causes deterioration of the circuit quality factor, leading to a deterioration in the phase noise performance. Likewise, some conventional techniques, such as banded design and adding switchable varactors, may degrade the maximum operational frequency and still produce some degradation in phase noise.
Accordingly, a need arises for techniques for extending the tuning range of a VCO that does not degrade VCO circuit performance.
Embodiments of methods and apparatuses may provide the capability to extend the tuning range of a VCO in a way that does not degrade VCO circuit performance. For example, the parasitic capacitance of semiconductor devices in the VCO circuit may be utilized to extend the tuning range of a VCO without significant degradation of VCO circuit performance.
For example, in an embodiment, a method voltage-control of an oscillator may comprise receiving a first signal for control of a frequency of an output signal from the oscillator, deriving a second signal from the first signal, controlling the frequency of the output signal from the oscillator using the first signal, and extending a frequency range of the oscillator using the second signal.
The second signal may be derived from the first signal by performing signal conditioning on the first signal. The signal conditioning may comprise frequency filtering the first signal. The frequency of the output signal may be controlled by controlling a capacitance of at least one voltage-variable capacitance with the first signal and the frequency range of the oscillator may be extended by controlling a parasitic capacitance of at least one amplifying element or a parasitic capacitance of the at least one voltage-variable capacitance with the second signal. At least one of the at least one amplifying element or the at least one voltage-variable capacitance may comprise a MOS device and the parasitic capacitance may be a drain to bulk diode parasitic capacitance of the MOS device. The signal conditioning may comprise analog signal conditioning. The signal conditioning may comprise digital signal conditioning.
For example, in an embodiment, a voltage-controlled oscillator may comprise voltage-controlled oscillator circuitry having a first input for receiving a first signal and configured to control of a frequency of an output signal from the oscillator using the first signal, and having a second input for receiving a second signal and configured to extend a frequency range of the oscillator using the second signal and signal conditioning circuitry configured to derive the second signal from the first signal.
For example, in an embodiment, an apparatus may comprise a voltage-controlled oscillator having a first input for receiving a first signal and configured to control of a frequency of an output signal from the oscillator using the first signal, and having a second input for receiving a second signal and configured to extend a frequency range of the oscillator using the second signal and signal conditioning circuitry configured to derive the second signal from the first signal.
The details of the present invention, both as to its structure and operation, can best be understood by referring to the accompanying drawings, in which like reference numbers and designations refer to like elements.
Embodiments of methods and apparatuses may provide the capability to extend the tuning range of a voltage-controlled oscillator (VCO) in a way that does not degrade VCO circuit performance. For example, the parasitic capacitance of semiconductor devices in the VCO circuit may be utilized to extend the tuning range of a VCO without significant degradation of VCO circuit performance.
An exemplary block diagram and circuit diagram 100 of an embodiment of a VCO is shown in
Circuit diagram 120 illustrates a simplified exemplary circuit configuration for VCO 102. In this example, VCO 102 includes amplifying elements 122A, B, voltage-variable capacitances 124A, B, inductance 126, and current sink 128. In this exemplary circuit diagram, amplifying elements 122A, B may typically be MOS devices, such as MOS-FET transistors, while voltage-variable capacitances 124A, B, may typically be varactor or varicap diodes, which may be implemented, for example, using MOS devices. Inductance 126 may typically be an on-chip or external inductor. Current sink 128 may absorb current from amplifying elements 122A, B. In this example, VCO 102 output frequency may be controlled by one or more voltage-variable capacitances 124A, B connected to the LC tank. VTune 106 may be applied to tuning input 110, and VD 112 may be applied to drain parasitic capacitance tuning inputs 114. Typically, VTune 106 may be used to control the frequency of the output signal 108 from VCO 102.
The frequency of the output signal 108 from VCO 102 may also be controlled by changing the parasitic capacitance of the drain/bulk diodes of amplifying elements 122A, B, which are connected to the tank circuitry (here LC). Drain parasitic capacitance tuning inputs 114 are connected to the bulk terminals or connections of amplifying elements 122A, B. When applied to drain parasitic capacitance tuning inputs 114, VD 112 biases the drain/bulk diodes of amplifying elements 122A, B, which alters the parasitic capacitances 128A, B of the drain/bulk diodes 122A, B. The parasitic capacitances 128A, B may change according to
Utilizing the parasitic capacitances of the drain/bulk diodes of amplifying elements 122A, B in VCO 102 may provide the capability to extend the tuning range of VCO 102 with little or no performance degradation.
In the example shown in
A simplified exemplary circuit diagram of a signal conditioner 104 is shown in
In this exemplary embodiment, signal conditional 104 operates as a non-linear amplifier. Use of such a signal conditioner may provide extension of the tuning range of the VCO and may prevent gain degradation at the band edges. In this example, signal conditioner 104 may include a n-channel transistor 206, an p-channel transistor 208, a first resistor 210, a second resistor 212, and a capacitor 214.
The transistors should have sufficient transconductance so that: (gm)−1<<R/2 for |VGS|>VT, where gm is the nmos/pmos transconductance, VGS is gate source voltage, and VT is the transistor threshold voltage. Then for Vin<VCC/2−VT 216: p-channel transistor operates as a source follower and the n-channel transistor is off. For VCC/2+VT>Vin>VCC/2−VT218, both transistors are off. For Vin>VCC/2+VT 220, the n-channel transistor operates as a source follower and the p-channel transistor is off. This may produce a transfer function 222 as shown in
Likewise, for |Vin−VCC/2|<VT: the output noise PSD is
In the example shown in
An example of extension of the VCO tuning range 300 and linearization of the gain 302 for the circuit examples shown in
The present invention may be a system and/or a method at any possible technical detail level of integration. Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims.
