Programmable tunable capacitor and voltage controlled oscillator

Abstract

Programmable tunable capacitor and voltage controlled oscillator. The programmable tunable capacitor includes a fixed variable capacitor controlled by a control voltage connected with a first polarity, and a plurality of conditional variable capacitors each conditionally controlled by the control voltage according to a plurality of logic signals. Each conditional variable capacitor has a first variable capacitor controlled by a first voltage connected with the first polarity, a second variable capacitor controlled by a second voltage connected with a second polarity, a first multiplexer to select between a first DC voltage and the control voltage according to a corresponding logic signal of the logic signals to output the first voltage, and a second multiplexer to select between a second DC voltage and an intermediate DC voltage according to the corresponding logic signal to output the second voltage.

Description

Technical Field

[0001] This invention relates to voltage-controlled oscillators, and more particularly to voltage-controlled oscillators with high programmable gain. Background Technology

[0002] As is well known, a voltage-controlled oscillator (VCO) outputs an oscillation signal, and the oscillation frequency of the oscillation signal is controlled by a control voltage. In this disclosure, the terms "oscillation frequency" and "oscillation frequency" used below are the same and interchangeable in the relevant description of the VCO. In one embodiment, the oscillation frequency is higher (lower) when the control voltage is higher (lower). The gain of the VCO is defined as the ratio between the incremental change in the oscillation frequency and the incremental change in the control voltage. A high-gain VCO is more sensitive to changes in its control voltage.

[0003] like Figure 1 As shown in the schematic diagram, a conventional VCO 100 includes a tunable resonant tank 110 and a regenerative network 120. The tunable resonant tank 110 is used to adjust the resonant voltage V according to the control voltage V. C The frequency of oscillation is determined by the regenerative network 120, which includes two N-channel metal-oxide-semiconductor (NMOS) transistors 121 and 122. The two NMOS transistors 121 and 122 are configured in a cross-coupling topology to establish negative resistance, providing energy to sustain oscillation. The tunable resonant tank 110 includes an inductor 111, a fixed capacitor 112, and a variable capacitor. The variable capacitor contains a control voltage V. C The control consists of two variable capacitors, 113 and 114. The center-tap connection of inductor 111 is referred to as "V". SP The power node is "VCO100". VCO100 is well known in the prior art and will not be described in detail here.

[0004] The resonant frequency f0 of the tunable resonant groove 110 is approximately equal to that in Equation 1.

[0005]

[0006] Where L is the inductance value of inductor 111, and C totThe total capacitance value is determined by the capacitor 112 and the two variable capacitors 113, 114. When the parasitic capacitance of the regeneration network 120 is significantly smaller than C tot , the oscillation frequency of the VCO 100 is approximately equal to the resonance frequency f0of the tunable resonant tank 110.

[0007] In the present disclosure, a variable capacitor is a two-terminal circuit element of a tunable capacitor, which includes a positive terminal marked with "+" and a negative terminal marked with "-". When the voltage of the positive terminal rises (falls), the capacitance value of the variable capacitor increases (decreases), and when the voltage of the negative terminal rises (falls), the capacitance value of the variable capacitor decreases (increases). When the positive terminal is connected to the control voltage used to control the tunable capacitor, the variable capacitor is said to be forward connected. When the negative terminal is connected to the control voltage used to control the tunable capacitor, the variable capacitor is said to be backward connected. That is, Figure 1 The two variable capacitors 113, 114 of the VCO 100 are obviously backward connected. Therefore, when the control voltage V C rises (falls), the capacitance values of the variable capacitors 113, 114 decrease (increase) and the total capacitance value C tot decreases (increases), thus the oscillation frequency of the VCO 100 increases (decreases). The gain (denoted by K VCO ) of the VCO 100, which is defined by the change in the oscillation frequency in response to the change in the control voltage V C , can be represented by Equation 2. VCO

[0008]

[0009] In implementation, the VCO 100 is generally integrated with a phase-locked loop to adjust the control voltage V C in a closed loop manner. In this case, K VCO plays an important role in the dynamics of the phase-locked loop. In many cases, it is desirable for the VCO to have a programmable gain. A larger K VCO can make the phase-locked loop respond faster, but inevitably makes the VCO 100 more susceptible to circuit noise, as circuit noise can cause a larger error in the oscillation frequency when the VCO gain is higher.

[0010] Therefore, it is desirable to have a VCO with a programmable gain, and to reduce the susceptibility to circuit noise when the VCO is programmed to have a high gain.​ SUMMARY

[0011] In an embodiment, the programmable tunable capacitor includes a fixed varactor and contingent varactors. The fixed varactor is controlled by a control voltage connected with a first polarity. The contingent varactors are conditionally controlled by the control voltage according to logic signals, respectively. Each contingent varactor includes a first varactor, a second varactor, a first multiplexer, and a second multiplexer. The first varactor is controlled by a first voltage connected with the first polarity. The second varactor is controlled by a second voltage connected with a second polarity. The first multiplexer is configured to select between a first direct-current (DC) voltage and the control voltage according to a corresponding logic signal of the logic signals to output the first voltage. The second multiplexer is configured to select between a second DC voltage and a medium DC voltage according to the corresponding logic signal to output the second voltage.

[0012] In an embodiment, the voltage-controlled oscillator includes a resonant tank and a regeneration network. The resonant tank includes an inductor, a capacitor, and a programmable tunable capacitor. The inductor, the capacitor, and the programmable tunable capacitor are connected in parallel to determine a frequency of an oscillation signal at a common-mode node according to a control voltage and logic signals. The regeneration network is configured to provide a negative resistance at the common-mode node to sustain an oscillation. The programmable tunable capacitor includes a fixed varactor and contingent varactors. The fixed varactor is controlled by the control voltage connected with a first polarity. The contingent varactors are conditionally controlled by the control voltage according to the logic signals, respectively. Each contingent varactor includes a first varactor, a second varactor, a first multiplexer, and a second multiplexer. The first varactor is controlled by a first voltage connected with the first polarity. The second varactor is controlled by a second voltage connected with a second polarity. The first multiplexer is configured to select between a first direct-current (DC) voltage and the control voltage according to a corresponding logic signal of the logic signals to output the first voltage. The second multiplexer is configured to select between a second DC voltage and a medium DC voltage according to the corresponding logic signal to output the second voltage. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 A schematic diagram of a prior art voltage-controlled oscillator.

[0014] Figure 2 A schematic diagram of a voltage-controlled oscillator according to an embodiment of the present disclosure.

[0015] Figure 3 Schematic diagram of a programmable tunable capacitor according to an embodiment of the present disclosure.

[0016] Symbol explanation

[0017] 100: Voltage controlled oscillator (VCO)

[0018] 110: Tunable resonant tank

[0019] 111: Inductor

[0020] 112: Capacitor

[0021] 113: Variable capacitor

[0022] 114: Variable capacitor

[0023] 120: Regeneration network

[0024] 121: NMOS transistor

[0025] 122: NMOS transistor

[0026] 200: Voltage controlled oscillator (VCO)

[0027] 210: Resonant tank

[0028] 211: Inductor

[0029] 212: Capacitor

[0030] 213: Programmable tunable capacitor

[0031] 220: Regeneration network

[0032] 221: NMOS transistor

[0033] 222: NMOS transistor

[0034] 300: Tunable capacitor

[0035] 310: Fixed variable capacitor

[0036] 311: Variable capacitor

[0037] 312: Variable capacitor

[0038] 320: Conditionally variable capacitor

[0039] 321: Variable capacitor

[0040] 322: Variable capacitor

[0041] 323: Variable capacitor

[0042] 324: variable capacitor

[0043] 325: multiplexer

[0044] 326: multiplexer

[0045] 330: conditional variable capacitor

[0046] 331: variable capacitor

[0047] 332: variable capacitor

[0048] 333: variable capacitor

[0049] 334: variable capacitor

[0050] 335: multiplexer

[0051] 336: multiplexer

[0052] 340: conditional variable capacitor

[0053] 341: variable capacitor

[0054] 342: variable capacitor

[0055] 343: variable capacitor

[0056] 344: variable capacitor

[0057] 345: multiplexer

[0058] 346: multiplexer

[0059] V SP : power supply node

[0060] V C : control voltage

[0061] 201: node

[0062] 202: node

[0063] V1: first voltage signal (voltage)

[0064] V2: second voltage signal (voltage)

[0065] A0, A1, A2: logic signal

[0066] V B0 , V B1 , V B2 : reverse voltage

[0067] V F0 , V F1 , VF2 Forward voltage

[0068] V H High DC voltage

[0069] V L Low DC voltage

[0070] V M Intermediate DC voltage Detailed Implementation

[0071] This disclosure relates to voltage-controlled oscillators. Although several embodiments of this disclosure are described in the specification, and these embodiments are considered preferred methods for implementing the invention, it should be understood that the invention can be implemented in various ways and is not limited to the specific examples described below, or to any particular manner of implementing any feature of these examples. In other instances, well-known details are not shown or described to avoid obscuring aspects of this disclosure.

[0072] Those skilled in the art will understand the microelectronics-related terminology and basic concepts used herein, such as "voltage," "DC voltage," "signal," "parallel connection," "circuit node," "ground," "power node," "metal oxide semiconductor (MOS) transistor," "complementary metal oxide semiconductor (CMOS) process technology," "n-channel metal oxide semiconductor (NMOS) transistor," "p-channel metal oxide semiconductor (PMOS) transistor," "variable capacitor," "capacitor," "capacitance value," and "multiplexer." Such terminology is used in the context of microelectronics, and the related concepts are self-evident to those skilled in the art; therefore, they will not be explained in detail here.

[0073] No need to specify nano-Henry (nH), pico-Farad (pF), femto-Farad (fF), nanometer (nm), or micrometer (micrometer). μm The terminology used by these organizations is explained so that those skilled in the art can understand it.

[0074] Without delving into the details of how one element in a circuit schematic is connected to another, those skilled in the relevant art can read a circuit schematic containing capacitors, NMOS transistors, and PMOS transistors. Those skilled in the relevant art can also recognize the symbols for a reference ground, a capacitor, an inductor, a variable capacitor, a tunable capacitor, and the symbols for a PMOS transistor and an NMOS transistor, and can recognize the "source terminal," the "gate terminal," and the "drain terminal" of the symbols for a PMOS transistor and an NMOS transistor. For brevity in the description, the "source terminal" is referred to as the "source," the "gate terminal" is referred to as the "gate," and the "drain terminal" is referred to as the "drain" for MOS transistors.

[0075] A circuit is a collection of at least one transistor, at least one capacitor, at least one resistor, and / or at least one other electronic device, and they are connected to each other in some manner to achieve a certain function.

[0076] In this document, a "circuit node" is often simply referred to as a "node" when it is clear from the context that the meaning of "node" is "circuit node."

[0077] A signal is a voltage of variable level that carries some information and can change over time. The level of a signal at a point in time represents the state of the signal at that point in time.

[0078] A logic signal is a voltage signal that has two states: a low state and a high state. The low state is also referred to as the "0" state. The high state is also referred to as the "1" state. When describing a logic signal Q as "high" ("high level") or "low" ("low level"), it means that the logic signal Q is in the high state; or the logic signal Q is in the low state. Similarly, when describing a logic signal Q as "1" or "0," it means that the logic signal Q is in the "1" state; or the logic signal Q is in the "0" state.

[0079] As previously described in the present disclosure, a variable capacitor is a two-terminal circuit element of a tunable capacitor, which includes a positive terminal marked with "+" and a negative terminal marked with "-". When the voltage of the positive terminal rises (falls), the capacitance value of the variable capacitor increases (decreases), and when the voltage of the negative terminal rises (falls), the capacitance value of the variable capacitor decreases (increases). The variable capacitor is called forward-connected when the positive terminal is connected to the control voltage used to control the tunable capacitor. The variable capacitor is called reverse-connected when the negative terminal is connected to the control voltage used to control the tunable capacitor. Further, in the present disclosure, the control voltage applied to the positive terminal of the forward-connected variable capacitor is called "forward voltage", and the control voltage applied to the negative terminal of the reverse-connected variable capacitor is called "reverse voltage". In the case where a circuit includes a forward-connected variable capacitor and a reverse-connected variable capacitor, one of the forward-connected variable capacitor and the reverse-connected variable capacitor is called connected to a first polarity, and the other is called connected to a second polarity.

[0080] A direct current voltage is a voltage level that is nearly stable.

[0081] Referring to Figure 2 , Figure 2 is a schematic diagram of a VCO 200 according to an embodiment of the present disclosure. The VCO 200 includes a resonant tank 210 and a regeneration network 220. The resonant tank 210 includes an inductor 211, a capacitor 212, and a programmable tunable capacitor 213. The inductor 211, the capacitor 212, and the programmable tunable capacitor 213 are configured in a parallel connection structure and are connected across a first node 201 and a second node 202 to determine a resonant frequency according to a control voltage V C and a plurality of logic signals A0, A1, A2,.... The regeneration network 220 includes two NMOS transistors 221, 222. The two NMOS transistors 221, 222 are configured in an intercoupling structure to provide a negative resistance between the first node 201 and the second node 202, thereby maintaining oscillation of a first voltage signal V1 at the node 201 and a second voltage signal V2 at the node 202. A center tap of the inductor 211 is connected to a power supply node V SP . Since the drain of the NMOS transistor 221 is connected to the gate of the NMOS transistor 222, and the drain of the NMOS transistor 222 is connected to the gate of the NMOS transistor 221, the NMOS transistor 221 and the NMOS transistor 222 are intercoupled. It is clear to those skilled in the art that the two MOS transistors configured in an intercoupling structure can provide a negative resistance to maintain oscillation, and thus will not be explained in detail here. The VCO 200 is similar to the VCO 100 of FIG. 1, and thus will not be explained in detail here. Figure 1The difference between the VCO 100 and the VCO 200 is that the two variable capacitors 113, 114 of the VCO 100 are replaced by the programmable tunable capacitor 213 of the VCO 200. Except for the aforementioned difference, the VCO 200 is identical to the VCO 100. Figure 1 The formula 1 can be used to calculate the resonant frequency of the resonant tank 210, where L of the formula 1 is the inductance value of the inductor 211, and C of the formula 1 is the total capacitance value determined by the capacitor 212 and the programmable tunable capacitor 213. tot In an embodiment, the parasitic capacitance of the regeneration network 220 is significantly smaller than C tot Therefore, the formula 1 can be used to calculate the oscillation frequency of the VCO 200.

[0082] Referring to Figure 3 , Figure 3 is a schematic diagram of a programmable tunable capacitor 300 according to an embodiment of the present disclosure. The tunable capacitor 300 can be used to implement the programmable tunable capacitor 213 of the VCO 200. The programmable tunable capacitor 300 is used to provide a tunable capacitance value between the two nodes 201, 202 according to the logic signals A0, A1, A2,..., the control voltage V C , and three DC voltages. The three DC voltages include a low DC voltage V L , a high DC voltage V H , and an intermediate DC voltage V M . Among them, the high DC voltage V H is greater than the low DC voltage V L , and the intermediate DC voltage V M is between the high DC voltage V H and the low DC voltage V L . The programmable tunable capacitor 300 includes a fixed variable capacitor 310 and a plurality of conditional variable capacitors 320, 330, 340,.... The fixed variable capacitor 310 and the conditional variable capacitors 320, 330, 340,... are connected in parallel. The conditionality of the conditional variable capacitors 320, 330, 340,... is determined by the logic signals A0, A1, A2,..., respectively. The fixed variable capacitor 310 includes two reversely connected variable capacitors 311, 312. The capacitance values of the two reversely connected variable capacitors 311, 312 are determined by the control voltage V CControl. Each conditional variable capacitor includes two reverse-connected variable capacitors, two forward-connected variable capacitors, and two multiplexers. The two reverse-connected variable capacitors of the conditional variable capacitor are controlled by a reverse voltage, and the two forward-connected variable capacitors are controlled by a forward voltage. The two multiplexers include a first multiplexer and a second multiplexer. The first multiplexer is used to control the variable capacitor based on a corresponding logic signal among the logic signals A0, A1, A2... at a high DC voltage V. H With control voltage V C The selection is made between these two options to output a reverse voltage. A second multiplexer is used to select the output voltage based on the corresponding logic signal, at a low DC voltage V. L With intermediate DC voltage V M The variable capacitor 320 (330, 340) is selected between two reverse-connected variable capacitors 321 (331, 341) and 322 (332, 342), which are connected by a reverse voltage V. B0 (V B1 V B2 Controlled by two forward-connected variable capacitors 323 (333, 343) and 324 (334, 344), which are controlled by a forward voltage V. F0 (V F1 V F2 The system includes a control unit; and two multiplexers, comprising a first multiplexer 325 (335, 345) and a second multiplexer 326 (336, 346). The first multiplexer 325 (335, 345) is used to control the system based on logic signals A0 (A1, A2) at a high DC voltage V. H With control voltage V C Choose between these options to output reverse voltage V. B0 (V B1 V B2 The second multiplexer 326 (336, 346) is used to, based on logic signals A0 (A1, A2), operate at a low DC voltage V. L With intermediate DC voltage V M Choose between these options to output a positive voltage V. F0 (V F1 V F2 ).

[0083] Conditional variable capacitors 320, 330, 340… operate on the same principle and have the same function and operation. For the sake of brevity, only conditional variable capacitor 320 will be described in detail. Any description applicable to conditional variable capacitor 320 also applies to conditional variable capacitors 330 and 340, except that logic signal A0 is replaced by logic signals A1 and A2 respectively, and the reverse voltage V… B0 Reverse voltage VB1 V B2 Replacement, positive voltage V F0 They are respectively subjected to positive voltage V F1 V F2 The multiplexer 325 is replaced by the first multiplexer 335 and 345 respectively, and the multiplexer 326 is replaced by the second multiplexer 336 and 346 respectively.

[0084] When logic signal A0 is "0", the multiplexer 325 selects a high DC voltage V. H As the reverse voltage V B0 Furthermore, the multiplexer 326 selects a low DC voltage V. L As the positive voltage V F0 In this case, the two reverse-connected variable capacitors 321 and 322 have a high DC voltage V H The fixed capacitance value is determined, and the two positively connected variable capacitors 323 and 324 have a low DC voltage V. L The fixed capacitance value is determined, and the total capacitance value of the conditionally variable capacitor 320 is fixed. When the logic signal A0 is "1", the multiplexer 325 selects the control voltage V. C As the reverse voltage V B0 Furthermore, the multiplexer 326 selects the intermediate DC voltage V. M As the positive voltage V F0 In this case, the two reverse-connected variable capacitors 321 and 322 have a control voltage V C The adjustable capacitance value is controlled by two positively connected variable capacitors 323 and 324, which are controlled by an intermediate DC voltage V. M The fixed capacitance value is determined, and the total capacitance value of the conditionally variable capacitor 320 is adjustable and depends on the control voltage V. C The total capacitance value of the conditionally variable capacitor 320 can thus be programmed to be fixed or adjustable. Therefore, the total capacitance value of the conditionally variable capacitor 320 is adjustable and varies according to the control voltage V. C The change, and the increase in the total capacitance value (which responds to the control voltage V) C The increase or change in the value depends on the state of logic signals A0, A1, A2, etc.

[0085] In one embodiment, all conditional variable capacitors 320, 330, and 340 are identical. In this embodiment, the increase in the total capacitance value (responding to the control voltage V) is determined by the number (or number) of logic signals A0, A1, A2... that are "1". Cthe increase of the oscillation frequency of the VCO 200 is large (small), i.e., the VCO 200 has a high (low) gain. Therefore, the gain of the VCO 200 is adjustable, and it can be programmed by setting the states of the logic signals A0, A1, A2,....

[0086] In one embodiment, the two reverse-connected variable capacitors 321, 322 and the two forward-connected variable capacitors 323, 324 are identical; the high DC voltage V H approximately equal to the upper limit of the first voltage signal VI and the second voltage signal V2; the low DC voltage V L approximately equal to the lower limit of the first voltage signal VI and the second voltage signal V2; the intermediate DC voltage V M approximately equal to the average of the first voltage signal VI and the second voltage signal V2; and the control voltage V C the nominal value of the control voltage V C varies around the average of the first voltage signal VI and the second voltage signal V2. In a typical oscillation example, the first voltage signal VI and the second voltage signal V2 have an upper limit of about twice the supply voltage of the supply node V SP a lower limit of about 0 volts (V), and an average of the supply voltage of the supply node V SP Therefore, when the logic signal A0 is "1", in a nominal case, the reverse voltage V B0 is approximately equal to the forward voltage V F0Furthermore, the two reverse-connected variable capacitors 321 and 322 and the two forward-connected variable capacitors 323 and 324 are all stable. Therefore, when the average voltage of the first voltage signal V1 at node 201 or the average voltage of the second voltage signal V2 at node 202 increases due to noise, the corresponding increase in the capacitance values ​​of the two reverse-connected variable capacitors 321 and 322 can be compensated by the corresponding decrease in the capacitance values ​​of the two forward-connected variable capacitors 323 and 324. When the logic signal A0 is "0", the two reverse-connected variable capacitors 321 and 322 and the two forward-connected variable capacitors 323 and 324 have approximately the same capacitance value. Therefore, when the average voltage of the first voltage signal V1 at node 201 or the average voltage of the second voltage signal V2 at node 202 increases due to noise, the corresponding increase in the capacitance values ​​of the two reverse-connected variable capacitors 321 and 322 can be compensated by the corresponding decrease in the capacitance values ​​of the two forward-connected variable capacitors 323 and 324. Therefore, regardless of the state of logic signal A0, the conditional variable capacitor 320 can be highly stable and unaffected by noise. In other words, regardless of the state of logic signals A0, A1, A2..., the programmable adjustable capacitor 213 can be highly stable and unaffected by noise.

[0087] Multiplexers are well known to those skilled in the art and will not be explained in detail here. Multiplexers 325, 326, 335, 336, 345, 346... can be implemented from any multiplexer circuit known in the prior art, depending on the needs of the circuit designer.

[0088] For example, but not limited to: VCO200 is manufactured on a silicon substrate using 55nm CMOS process technology; power node V SPthe voltage of the inductor 211 is 700 millivolt (mV); the capacitance of the capacitor 212 is 1.45 pf; the NMOS transistors 221, 222 are identical, and each of them has a "W / L" (which represents width / length) of 30 μm / 60 nm; the two reverse-connected variable capacitors 311, 312 are identical, each of them has a "W / L" of 24 μm / 200 nm, and each of them has a capacitance value of 77.8 fF, 63.4 fF, and 36.2 fF, respectively, when the voltage difference between the "+" terminal and the "-" terminal of each of them is 1.2 V, 0 V, and -1.2 V, respectively; the four conditional variable capacitors are identical, and all of the four conditional variable capacitors are identical, each of them has a "W / L" of 6 μm / 200 nm, and each of them has a capacitance value of 19.4 fF, 15.8 fF, and 9.1 fF, respectively, when the voltage difference between the "+" terminal and the "-" terminal of each of them is 1.2 V, 0 V, and -1.2 V, respectively; and the VCO 200 has a nominal oscillation frequency of about 8 gigahertz (GHz), and has a gain of about 60 megahertz / volt (MHz / V) when all of the logic signals A0, A1, A2,... are "1", and has a gain of about 30 megahertz / volt (MHz / V) when all of the logic signals A0, A1, A2,... are "0".

[0089] The programmable tunable capacitor 300 is an embodiment that aims to make the VCO 200 have a positive gain. In this embodiment, the increase of the control voltage V C results in the decrease of the total capacitance value of the programmable tunable capacitor 300, and thus results in the increase of the oscillation frequency. If a negative gain is desired, the following operations can be performed: replace all of the reverse-connected variable capacitors with forward-connected variable capacitors, and replace all of the forward-connected variable capacitors with reverse-connected variable capacitors; and replace the high DC voltage V H with the low DC voltage V L , and replace the low DC voltage V L with the high DC voltage V HSubstitutions. Since the present disclosure can be applied to a VCO with either positive or negative gain, and "reverse connected" and "forward connected" can be interchanged, in the claims the terms "connected in a first polarity" and "connected in a second polarity" are used. In the case of positive gain, "connected in a first polarity" and "connected in a second polarity" refer to "reverse connected" and "forward connected", respectively, and in the case of negative gain, "connected in a first polarity" and "connected in a second polarity" refer to "forward connected" and "reverse connected", respectively. Similarly, "first DC voltage" and "second DC voltage" are used, where in the case of positive gain, "first DC voltage" and "second DC voltage" refer to "high DC voltage" and "low DC voltage", respectively, and in the case of negative gain, "first DC voltage" and "second DC voltage" refer to "low DC voltage" and "high DC voltage", respectively. Likewise, "first bounds" and "second bounds" are used, where in the case of positive gain, "first bounds" and "second bounds" refer to "upper bounds" and "lower bounds", respectively, and in the case of negative gain, "first bounds" and "second bounds" refer to "lower bounds" and "upper bounds", respectively.

[0090] The present disclosure can be applied to VCOs of other configurations, for example, using PMOS transistors to implement negative resistance, or using NMOS transistors and PMOS transistors to implement negative resistance. Therefore, in the claims the term "MOS transistor" is used.

[0091] VCO 200 is a differential circuit configuration, where the oscillation signal is a differential signal. A differential signal includes two voltages VI and V2, which are nearly constant and complementary, i.e., the amount of change in voltage VI is always accompanied by roughly the same amount of opposite change in voltage V2. This is one example, but is not limited thereto. The present disclosure is also applicable to VCOs of single-ended circuit configuration, for example, a Colpitts oscillator, which includes a capacitor to tune the oscillation frequency. The present disclosure can be applied to a Colpitts oscillator by replacing the capacitor with a half of the circuit of programmable adjustable capacitor 300, where a half of the circuit can be, for example, removing variable capacitors 312, 322, 324, 332, 334, 342, 344, etc.

[0092] Those skilled in the art will readily observe that numerous modifications and changes can be made to the devices and methods without departing from the scope of the present disclosure. Accordingly, the above should not be taken as limiting the present disclosure, but rather the only limitations are those set forth in the claims that follow.

Claims

1. A programmable adjustable capacitor, comprising: A fixed variable capacitor, controlled by a control voltage connected with a first polarity; and Several conditional variable capacitors are conditionally controlled by the control voltage according to several logic signals, wherein each conditional variable capacitor comprises: A first variable capacitor, controlled by a first voltage connected with the first polarity; A second variable capacitor, controlled by a second voltage connected with a second polarity, is connected in parallel with the first variable capacitor; A first multiplexer is configured to select between a first DC voltage and a control voltage based on a corresponding logic signal from among the logic signals, so as to output the first voltage; and A second multiplexer is used to select between a second DC voltage and an intermediate DC voltage according to the corresponding logic signal, so as to output the second voltage.

2. The programmable adjustable capacitor as claimed in claim 1, wherein the fixed variable capacitor and the conditional variable capacitors are connected in parallel to an oscillation signal at a common-mode node.

3. The programmable adjustable capacitor as claimed in claim 2, wherein the first DC voltage is equal to a first limit of the oscillation signal, and the second DC voltage is equal to a second limit of the oscillation signal.

4. The programmable adjustable capacitor as described in claim 3, wherein, When the control voltage rises, the first limit of the oscillation signal becomes an upper limit of the oscillation signal, and the second limit of the oscillation signal becomes a lower limit of the oscillation signal, the capacitance value of the fixed variable capacitor decreases.

5. A voltage-controlled oscillator comprising a resonant tank and a regenerative network, the resonant tank comprising an inductor, a capacitor, and a programmable adjustable capacitor, the inductor, the capacitor, and the programmable adjustable capacitor being connected in parallel to determine a frequency of an oscillation signal at a common-mode node based on a control voltage and a plurality of logic signals, the regenerative network being used to provide a negative resistance at the common-mode node to maintain an oscillation, wherein... The programmable adjustable capacitor includes a fixed variable capacitor and a plurality of conditional variable capacitors. The fixed variable capacitor is controlled by a control voltage connected with a first polarity. The conditional variable capacitors are conditionally controlled by the control voltage according to logic signals. Each conditional variable capacitor includes: A first variable capacitor, controlled by a first voltage connected with the first polarity; A second variable capacitor, controlled by a second voltage connected with a second polarity, is connected in parallel with the first variable capacitor; A first multiplexer is configured to select between a first DC voltage and a control voltage based on a corresponding logic signal from among the logic signals, so as to output the first voltage; and A second multiplexer is used to select between a second DC voltage and an intermediate DC voltage according to the corresponding logic signal, so as to output the second voltage.

6. The voltage-controlled oscillator as claimed in claim 5, wherein the first DC voltage is equal to a first limit of the oscillation signal, and the second DC voltage is equal to a second limit of the oscillation signal.

7. The voltage-controlled oscillator as claimed in claim 5, wherein the intermediate DC voltage is equal to a nominal value of the control voltage.

8. The voltage-controlled oscillator as claimed in claim 5, wherein the intermediate DC voltage is equal to an average voltage of the oscillation signal.

9. The voltage-controlled oscillator as described in claim 6, wherein, When the control voltage rises, the first limit of the oscillation signal becomes an upper limit of the oscillation signal, and the second limit of the oscillation signal becomes a lower limit of the oscillation signal, the capacitance value of the fixed variable capacitor decreases.

10. The voltage-controlled oscillator as described in claim 6, wherein, When the control voltage rises, the first limit of the oscillation signal is the lower limit of the oscillation signal, and the second limit of the oscillation signal is the upper limit of the oscillation signal, the capacitance value of the fixed variable capacitor increases.

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