Differential cross-coupling voltage-controlled oscillator with CLASS-D structure

Abstract

The invention belongs to the field of oscillators, particularly relates to a differential cross-coupling voltage-controlled oscillator of a CLASS-D structure, and aims to solve the problem that the advantages of low power consumption, extremely low noise, wide frequency regulation range and complete output waveform cannot be achieved in the prior art. According to the invention, a resonance stage module and a filtering stage module are connected through blocking capacitors Cm1 and Cm2; the resonance level module is based on a CLASS-D structure and is used for generating an oscillation signal with extremely low noise, and the frequency of the oscillation signal is adjusted through frequency band selection and a variable capacitance diode; and the filtering stage module is used for carrying out band-pass filtering and swing adjustment on the signal generated by the resonance stage module, realizing distortion waveform recovery and outputting a pair of differential sine wave signals. The circuit has the advantages of extremely low noise, wide frequency adjustment range, good signal integrity, low power consumption and the like.

Description

Technical Field

[0001] The invention belongs to the field of oscillators, and in particular relates to a differential cross-coupled voltage-controlled oscillator with a CLASS-D structure. Background Art

[0002] Voltage controlled oscillators are widely used in modern integrated circuit systems such as communication systems, clock data recovery circuits, frequency synthesizers, and wired / wireless transceivers. In the early days of low-frequency, noise-insensitive integrated circuit chips, smaller ring oscillators were generally used. However, with the advancement of technology, the frequency of communication systems has developed in a higher direction, which has put forward higher requirements on the frequency and noise performance of the clock generation circuit in the supporting chip, and the use of LC type voltage controlled oscillators has become more and more common.

[0003] However, in the traditional CLASS-B structure LC type voltage-controlled oscillator, the tail current source contributes more flicker noise and thermal noise. In order to suppress this noise, the industry has proposed a CLASS-D structure voltage-controlled oscillator, which has lower noise.

[0004] However, the existing voltage-controlled oscillators based on the CLASS-D structure do not meet the requirements for signal integrity and frequency adjustment range, and cannot meet some application scenarios that require the identification of a wider range of transition edges. Summary of the invention

[0005] In order to solve the above-mentioned problems in the prior art, that is, the prior art cannot achieve the advantages of low power consumption, extremely low noise, wide frequency adjustment range, and complete output waveform, the present invention provides a differential cross-coupled voltage-controlled oscillator with a CLASS-D structure, the oscillator includes a resonant stage module and a filter stage module, the resonant stage module and the filter stage module are connected by a DC isolation capacitor C m1 and C m2 connect;

[0006] The resonant stage module is based on a CLASS-D structure and is used to generate an extremely low-noise oscillation signal, the frequency of which is adjusted by frequency band selection and a varactor diode;

[0007] The filter stage module performs band-pass filtering and swing adjustment on the signal generated by the resonance stage module to restore the distorted waveform and output a pair of differential sine wave signals.

[0008] In some preferred embodiments, the resonant stage module includes a filter circuit, a common mode voltage regulation circuit, a differential inductor L connected in sequence. TANK , band selection module, differential varactor circuit, cross-coupled transistor pair M N1 and M N2 .

[0009] In some preferred embodiments, the frequency band selection module includes M frequency modulation units;

[0010] The frequency modulation capacitance values ​​of the M frequency modulation units are geometric progression {C TANK , 2C TANK 、4C TANK , ..., 2 M-1 C TANK}; where M is the frequency modulation accuracy of the voltage controlled oscillator.

[0011] In some preferred embodiments, the two frequency modulation capacitors C of the M frequency modulation units TANK One end is connected to the differential inductor L TANK The two arms TANKN and TANKP, the other end is connected in series with a series resistor R TANK11 and R TANK12 ;

[0012] Series resistance R TANK11 and R TANK12 The two ends of the transistor switch M are connected across R11 The source and drain of the transistor switch M R11 、M R12 、M R13 The gate of the external input signal SW is connected CAP , transistor switch M R12 The source of the external input reference voltage V REF , transistor switch M R12 、M R13 The drain connected series resistor R TANK11 and R TANK12 The middle node of transistor switch M R13 The source is grounded.

[0013] In some preferred embodiments, the method for adjusting the frequency of the voltage-controlled oscillator of the frequency modulation unit includes:

[0014] When the external input signal SW CAP For high level signals, two FM capacitors C TANK The transistor switch M plays a capacitive role in the resonant stage of the voltage controlled oscillator. R11 On, series resistance R TANK11 and R TANK12 is short-circuited, transistor M R12 、M R13 The switch combination gives the series resistor R TANK11 and R TANK12 The middle node outputs a low level;

[0015] When the external input signal SW CAP For low level signals, two FM capacitors C TANKThe transistor switch M does not play a capacitive role in the resonant stage of the voltage controlled oscillator. R11 Disconnect, series resistor R TANK11 and R TANK12 Access circuit, transistor M R12 、M R13 The switch combination outputs the reference voltage V REF .

[0016] In some preferred embodiments, the differential varactor circuit includes a varactor diode C var1 and C var2 , series resistance R var1 and R var2 , capacitor C a1 and C a2 ;

[0017] Varactor diode C var1 and C var2 The two source / drain terminals are connected to the differential control voltage positive terminal V CP , the two gates are connected to capacitors C a1 and C a2 one end of

[0018] Capacitor C a1 and C a2 The other end is connected to the differential inductor L TANK The two arms TANKN and TANKP;

[0019] Series resistance R var1 and R var2 Connect a variable capacitance diode C across both ends of var1 and C var2 The two gates are connected in series with a resistor R var1 and R var2 The middle node is connected to the negative terminal of the differential control voltage V CN .

[0020] In some preferred embodiments, the method for adjusting the frequency of a voltage-controlled oscillator of the differential varactor circuit includes:

[0021] Differential inductance L TANK The common-mode voltage on the two arms TANKP and TANKN is equal, and the differential control voltage V CP and V CN Equivalent to varactor diode C var1 and C var2 The voltage difference between the two ends is ΔV = V CP -V CN Influence of varactor diode C var1 , C var2 Capacitance value;

[0022] The larger the ΔV, the larger the capacitance of the varactor diode C var1 , C var2 The smaller the capacitance, the higher the voltage-controlled oscillator frequency;

[0023] The smaller ΔV is, the smaller the capacitance of the variable capacitance diode C is. var1 , C var2 The larger the capacitance, the lower the voltage controlled oscillator frequency.

[0024] In some preferred embodiments, the filter stage module includes a common mode voltage regulating resistor, a differential inductor L connected in sequence. BPF , bandpass selection module, bandpass filter resistor R BPF , transistor pair M N3 and M N4 , swing control current limiting resistor R BIAS .

[0025] In some preferred embodiments, the bandpass selection module includes N bandpass selection units;

[0026] The frequency modulation capacitance values ​​of the N bandpass selection units are a geometric progression {C BPF , 2C BPF 、4C BPF , ..., 2 N-1 C BPF}; where N is the adjustment accuracy of the filter passband.

[0027] In some preferred embodiments, the method for adjusting the amplitude of the output signal of the filter stage module includes:

[0028] The swing control current limiting resistor R BIAS Under the action of the output stage common mode voltage V CM2 and the resonant stage common mode voltage V CM Can be modulated separately:

[0029] V CM2 =Range2+V BIAS ;

[0030] Among them, Range2 is the output swing of the filter stage, V BIAS is the current limiting voltage on the current limiting control resistor;

[0031] Range2=(V BIAS / R BIAS / 2)×ro 34 ;

[0032] Among them, 34 For transistor M N3 and M N4 On-resistance;

[0033] After modulation, the common mode voltage of the output signals OUTP and OUTN is V CM2 , the output swing is V CM2 -V BIAS .

[0034] Beneficial effects of the present invention:

[0035] (1) Low noise: The differential cross-coupled voltage-controlled oscillator of the CLASS-D structure of the present invention optimizes the tail current source, and the flicker noise and thermal noise generated by the tail current transistor are optimized as a whole. In addition, the switch structure in the band selection module is specially optimized, and the PMOS transistor M is used to select the low noise. R12 and NMOS transistor M R13 The drain of is connected to the middle node of the series resistor, and the switch control signal SW CAP When the high voltage and low voltage are switched, the charge in the transistor channel can flow from the off side to the on side without affecting the load capacitance C. TANK It creates an impact and suppresses the noise contribution of the switching tube to the oscillator. In addition, the secondary circuit bandpass filter filters the oscillation signal generated by the resonant stage circuit again and limits the swing of the output signal. For a sinusoidal wave signal, the swing is reduced and the slope of the signal transition edge is controlled, further suppressing the output noise of the oscillator.

[0036] (2) Good signal integrity: Since the output waveform common mode value generated by the traditional CLASS-D structure voltage-controlled oscillator is V CM , and the swing is 2V CM , which generates distortion at the ground voltage of the signal and cannot meet the application scenarios that require a wider range of jump edges to be identified. In addition to bandpass filtering, the filter stage circuit of the differential cross-coupled voltage-controlled oscillator of the CLASS-D structure of the present invention can also limit the swing of the output signal to V CM2 -V BIAS , ensuring the integrity of the output signal, making it suitable for a wider range of application scenarios, and optimizing the additional power consumption caused by the additional shaping circuit part.

[0037] (3) Wide frequency adjustment range: The differential cross-coupled voltage-controlled oscillator of the CLASS-D structure of the present invention optimizes the tail current source. Under the premise of ensuring that the size of the cross-coupled transistor pair is sufficient, it can achieve a very large frequency output range. Combined with the frequency adjustment function of the band selection module and the varactor diode pair, the controllable range of the output frequency is further expanded. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0039] Figure 1 It is a schematic diagram of the overall structure of a differential cross-coupled voltage-controlled oscillator of a CLASS-D structure of the present invention;

[0040] Figure 2 It is a principle diagram of a frequency band selection module of a differential cross-coupled voltage-controlled oscillator of a CLASS-D structure of the present invention;

[0041] Figure 3 It is a schematic diagram of a bandpass selection module of a differential cross-coupled voltage-controlled oscillator of a CLASS-D structure of the present invention;

[0042] Figure 4 It is a schematic diagram for explaining the swing correction of a differential cross-coupled voltage-controlled oscillator of a CLASS-D structure of the present invention;

[0043] Figure 5 It is a schematic diagram illustrating bandpass filtering of a differential cross-coupled voltage-controlled oscillator with a CLASS-D structure of the present invention. DETAILED DESCRIPTION

[0044] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It is also necessary to explain that, for ease of description, only the parts related to the relevant invention are shown in the accompanying drawings.

[0045] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0046] The present invention discloses a differential cross-coupled voltage-controlled oscillator with a CLASS-D structure, wherein the oscillator comprises a resonant stage module and a filter stage module, wherein the resonant stage module and the filter stage module are connected via a DC isolation capacitor C m1 and C m2 connect;

[0047] The resonant stage module is based on a CLASS-D structure and is used to generate an extremely low-noise oscillation signal, the frequency of which is adjusted by frequency band selection and a varactor diode;

[0048] The filter stage module performs band-pass filtering and swing adjustment on the signal generated by the resonance stage module to restore the distorted waveform and output a pair of differential sine wave signals.

[0049] In order to more clearly explain the differential cross-coupled voltage-controlled oscillator of the CLASS-D structure of the present invention, the following is combined with Figure 1 Each module in the embodiment of the present invention is described in detail.

[0050] A differential cross-coupled voltage-controlled oscillator of a CLASS-D structure of the present invention comprises a resonant stage module, a filter stage module and a DC isolation capacitor C connected to the resonant stage module and the filter stage module. m1 and C m2 , each module is described in detail as follows:

[0051] like Figure 1 As shown, the differential inductance L of the resonant stage module TANK One arm TANKP is connected to the DC blocking capacitor C m1 One end of the DC blocking capacitor C m1 The other end is connected to the transistor pair M of the filter stage module N4 The gate of

[0052] The differential inductance L of the resonant stage module TANK One arm TANKN is connected to the DC blocking capacitor C m2 One end of the DC blocking capacitor C m2 The other end is connected to the transistor pair M of the filter stage module N3 of the gate.

[0053] like Figure 1 As shown, the resonant stage module includes a filter circuit, a common mode voltage regulation circuit, and a differential inductor L connected in sequence. TANK , band selection module, differential varactor circuit, cross-coupled transistor pair M N1 and M N2 .

[0054] The filter circuit includes a parallel power filter capacitor C VDD And the power filter resistor R VDD , one end of the parallel connection is connected to the input power supply VDD, and the other end is connected to the common mode voltage regulation circuit;

[0055] The common mode voltage regulation circuit includes a common mode voltage regulation resistor R CM , one end is connected to the filter circuit, and the voltage at the other end is reduced to V CM And connect the differential inductor L TANK The middle tap;

[0056] Differential inductance L TANK The two arms are the differential output ports TANKP and TANKN of the resonant cavity respectively;

[0057] The input terminal of the frequency band selection module, the input terminal of the differential varactor circuit, and the cross-coupled transistor pair M N1 The drain and M N2The gate of the differential output port TANKN is connected; the output end of the band selection module, the output end of the differential varactor circuit, and the cross-coupled transistor pair M N1 The gate and M N2 The drain of is connected to the differential output port TANKP;

[0058] Cross-coupled transistor pair M N1 The source and M N2 The source is grounded.

[0059] The differential varactor circuit includes a varactor diode C var1 and C var2 , series resistance R var1 and R var2 , capacitor C a1 and C a2 ;

[0060] Varactor diode C var1 and C var2 The two source / drain terminals are connected to the differential control voltage positive terminal V CP , the two gates are connected to capacitors C a1 and C a2 one end of

[0061] Capacitor C a1 and C a2 The other end is connected to the differential inductor L TANK The two arms TANKN and TANKP;

[0062] Series resistance R var1 and R var2 Connect a variable capacitance diode C across both ends of var1 and C var2 The two gates are connected in series with a resistor R var1 and R var2 The middle node is connected to the negative terminal of the differential control voltage V CN .

[0063] like Figure 2 As shown, the frequency band selection module includes M frequency modulation units, and the frequency modulation capacitance values ​​of the M frequency modulation units are geometric progression {C TANK , 2C TANK 、4C TANK , ..., 2 M-1 C TANK}; where M is the frequency modulation accuracy of the voltage controlled oscillator.

[0064] Two frequency modulation capacitors C of the M frequency modulation units TANK One end is connected to the differential inductor L TANK The two arms TANKN and TANKP, the other end is connected in series with a series resistor R TANK11 and RTANK12 ;

[0065] Series resistance R TANK11 and R TANK12 The two ends of the transistor switch M are connected across R11 The source and drain of the transistor switch M R11 、M R12 、M R13 The gate of the external input signal SW is connected CAP , transistor switch M R12 The source of the external input reference voltage V REF , transistor switch M R12 、M R13 The drain connected series resistor R TANK11 and R TANK12 The middle node of transistor switch M R13 The source is grounded.

[0066] In the band selection module, the differential inductor L TANK The two arms TANKP and TANKN are connected to the two output ports of the band selection module respectively. The input signal of the module includes the band selection control signal SW CAP [M:1] and reference voltage V REF The module contains M frequency modulation units, where M is the frequency modulation accuracy of the voltage-controlled oscillator. The frequency modulation capacitor values ​​of different frequency modulation units are geometric progressions, namely C TANK , 2C TANK 、4C TANK , ..., 2 M-1 C TANK Except for the different capacitance values ​​of the frequency modulation capacitors, the other circuits of the M frequency modulation units are completely the same.

[0067] In the frequency modulation unit with the smallest capacitance, two frequency modulation capacitors C TANK One end of each is used as the output port of the frequency modulation selection module and the differential inductor L TANK The two arms TANKP and TANKN are connected, and the other end of the capacitor is connected to two series resistors R TANK11 and R TANK12 The two series resistors are connected to an NMOS transistor switch M R11 The source and drain are connected in parallel, and the transistor switch M R11 The control signal is connected to the external input signal SW CAP [1], series resistance R TANK11 and R TANK12 The intermediate node and the PMOS transistor switch M R12 The drain connection of the transistor switch M R12 The gate of the external input signal SW CAP [1], transistor switch MR12 The source is connected to the external input reference voltage V REF , series resistance R TANK11 and R TANK12 The intermediate node is also connected to the NMOS transistor switch M R13 The drain connection of the transistor switch M R13 The gate of the external input signal SW CAP [1], transistor switch M R13 The source is grounded.

[0068] In the FM unit with the largest capacitance, two FM capacitors 2 M-1 C TANK One end of the capacitor is used as the output port of the frequency modulation selection module and connected to the two arms of the differential inductor TANKP and TANKN. The other end of the capacitor is connected to two series resistors R TANKM1 and R TANKM2 The two series resistors are connected to an NMOS transistor switch M RM1 The source and drain are connected in parallel, and the transistor switch M RM1 The control signal is connected to the external input signal SW CAP [M], series resistance R TANKM1 and R TANKM2 The intermediate node and the PMOS transistor switch M RM2 The drain connection of the transistor switch M RM2 The gate of the external input signal SW CAP [M], transistor switch M RM2 The source is connected to the external input reference voltage V REF , series resistance R TANKM1 and R TANKM2 The intermediate node is also connected to the NMOS transistor switch M RM3 The drain connection of the transistor switch M RM3 The gate of the external input signal SW CAP [M], transistor switch M RM3 The source is grounded.

[0069] The method for implementing the frequency adjustment of the voltage controlled oscillator by the frequency modulation unit of the present invention can be divided into the following two cases:

[0070] Case 1: SW CAP [1] is a high level signal, it is expected that the frequency modulation capacitor C TANK The transistor switch M R11 The two series resistors connected in parallel with the switch are short-circuited, which is equivalent to a pair of series FM capacitors C TANKDirectly connected to the two arms of the inductor TANKP and TANKN, the capacitive load is connected to the resonant cavity, reducing the output frequency of the voltage-controlled oscillator. R12 and NMOS transistor M R13 The formed switch group outputs a low level to the middle node of the resistor, and the middle node of the short-circuited series resistor is grounded.

[0071] Case 2: SW CAP [1] is a low level signal, the expected frequency modulation capacitor C TANK The capacitive effect does not play a role in the resonant stage of the voltage controlled oscillator. At this time, the transistor switch M R11 The two series resistors connected in parallel with the switch are connected to the circuit. At this time, the PMOS transistor M R12 and NMOS transistor M R13 The switch combination outputs the reference voltage V REF At this time, the load provided by the FM capacitor in the resonant cavity is smaller, and the frequency of the voltage-controlled oscillator is higher than that in the above case 1.

[0072] In the varactor diode pair circuit, the differential control voltage V CP and V CN The input signal is , under different differential voltages, the capacitance of the varactor diode is different, thus changing the output frequency of the voltage controlled oscillator. The capacitor C is directly connected to the two arms of the differential inductor, TANKP and TANK. a1 and C a2 The other end of the capacitor is connected to the core of the differential varactor diode, and the positive terminal of the differential control voltage V CP With the varactor diode C var1 , C var2 The source / drain connection of the two varactor diodes, the gate of the two varactor diodes as the output port of the differential varactor diode core circuit, the differential control voltage positive and negative terminals V CN With series resistor R var1 , R var2 The middle node is connected, and the outer ports of the two resistors are connected in parallel with the output port of the differential varactor diode to the core circuit.

[0073] The method by which the differential varactor diode pair achieves frequency regulation is:

[0074] The common-mode voltage on the two arms of the inductor, TANKP and TANKN, is equal, and the resistor R var1 , R var2 The voltages at both ends can be equivalent, and the differential control voltage V CP and V CN Equivalent to varactor diode C var1 and C var2 The voltage difference between the two ends is ΔV = V CP -V CNImpact C var1 , C var2 The larger the capacitance value of ΔV, the larger the capacitance of C var1 , C var2 The smaller the capacitance, the higher the voltage controlled oscillator frequency. Conversely, the smaller ΔV is, the higher the frequency of C var1 , C var2 The larger the capacitance, the lower the voltage-controlled oscillator frequency. Through the above method, the effect of differential voltage control frequency is achieved.

[0075] The common mode value and swing of the resonant stage are determined by transistor M N1 and M N2 The on-resistance ro 12 And it is determined by the current value of this stage. It and the filter stage can be changed and adjusted according to design requirements.

[0076] The common-mode value is calculated under the large signal model, at this time through the transistor M N1 and M N2 The current magnitude is V CM / ro 12 ;

[0077] Because the current between the inductor tap and the power supply in the resonant stage circuit is twice the above current, that is, it flows through the resistor R CM The current is 2(V CM / ro 12 );

[0078] Combined with Formula V CM =VDD-2(V CM / ro 12 )×(R CM +R VDD );

[0079] Can get

[0080] like Figure 1 As shown, the filter stage module includes a common-mode voltage adjustment resistor, a differential inductor L connected in sequence. BPF , bandpass selection module, bandpass filter resistor R BPF , transistor pair M N3 and M N4 , swing control current limiting resistor R BIAS .

[0081] In the filter stage circuit: power supply signal VDD and common mode voltage adjustment resistor R CM2 The voltage at the other end of the common-mode voltage adjustment resistor is reduced to V CM2 , connected to the differential inductor L BPF The tap, differential inductance L BPFThe two arms are the differential output ports OUTP and OUTN of the overall circuit, the bandpass selection module, the bandpass filter resistor R BPF , filter stage circuit input NMOS transistor pair M N3 and M N4 The drain of the differential inductor L BPF Two arms connected, M N3 and M N4 The source voltage is V BIAS , connect the swing control current limiting resistor R BIAS , R BIAS The other end is grounded, and the differential inductor L BPF , the capacitance value and bandpass filter resistor R provided by the bandpass selection module BPF Together they form the core part of the filter-level circuit, achieving a bandpass filtering effect in the frequency domain.

[0082] like Figure 3 As shown, the bandpass selection module includes N bandpass selection units, and the frequency modulation capacitor values ​​of the N bandpass selection units are geometric progression {C BPF , 2C BPF 、4C BPF , ..., 2 N-1 C BPF}; where N is the adjustment accuracy of the filter passband.

[0083] In the passband selection module, the differential inductor L BPF The two arms OUTP and OUTN are connected to the two output ports of the bandpass selection module respectively. The input signal of the module contains the band selection control signal SW BPF [N:1] and reference voltage V REF The module contains N bandpass selection units, where N is the adjustment accuracy of the filter bandpass. The frequency modulation capacitor values ​​of different bandpass selection units are geometric progressions, which are C BPF , 2C BPF 、4C BPF , ..., 2 N-1 C BPF ,The circuit structure of the bandpass selection unit is consistent with that of the frequency modulation unit.

[0084] In the bandpass unit with the minimum capacitance, two bandpass selection capacitors C BPF One end of each is used as the output port of the frequency modulation selection module and the differential inductor L BPF The two arms OUTP and OUTN are connected, and the other end of the capacitor is connected to two series resistors R BPF11 and R BPF12 The two series resistors are connected to an NMOS transistor switch M R211 The source and drain are connected in parallel, and the transistor switch M R211The control signal is connected to the external input signal SW BPF [1], series resistance R BPF11 and R BPF12 The intermediate node and the PMOS transistor switch M R212 The drain connection of the transistor switch M R212 The gate of the external input signal SW BPF [1], transistor switch M R212 The source is connected to the external input reference voltage V REF , series resistance R BPF11 and R BPF12 The intermediate node is also connected to the NMOS transistor switch M R213 The drain connection of the transistor switch M R213 The gate of the external input signal SW BPF [1], transistor switch M R213 The source is grounded.

[0085] In the bandpass unit with the largest capacitance, two bandpass selection capacitors 2 N-1 C BPF One end of each is used as the output port of the frequency modulation selection module and the differential inductor L BPF The two arms OUTP and OUTN are connected, and the other end of the capacitor is connected to two series resistors R BPFN1 and R BPFN2 The two series resistors are connected to an NMOS transistor switch M R2N1 The source and drain are connected in parallel, and the transistor switch M R2N1 The control signal is connected to the external input signal SW BPF [N], series resistance R BPFN1 and R BPFN2 The intermediate node and the PMOS transistor switch M R2N2 The drain connection of the transistor switch M R2N2 The gate of the external input signal SW BPF [N], transistor switch M R2N2 The source is connected to the external input reference voltage V REF , series resistance R BPFN1 and R BPFN2 The intermediate node is also connected to the NMOS transistor switch M R2N3 The drain connection of the transistor switch M R2N3 The gate of the external input signal SW BPF [N], transistor switch M R2N3 The source is grounded.

[0086] The method of implementing the frequency adjustment of the voltage-controlled oscillator by the bandpass selection unit can be divided into the following two cases:

[0087] Case 3: SW BPF[1] is a high level signal, it is expected that the passband selection capacitor C BPF The transistor switch M R211 The two series resistors connected in parallel with the switch are short-circuited, which is equivalent to a pair of series-connected passband selection capacitors C BPF Directly connected to the two arms of the inductor OUTP, OUTN, the capacitive load is connected to the filter circuit, reducing the filter passband of the bandpass filter, and the PMOS transistor M R212 and NMOS transistor M R213 The formed switch group outputs a low level to the middle node of the resistor, and the middle node of the short-circuited series resistor is grounded.

[0088] Case 4: SW BPF [1] When the signal is low level, the desired passband selection capacitor C BPF In the filter stage circuit, the capacitive effect is not played. At this time, the transistor switch M R211 The two series resistors connected in parallel with the switch are connected to the circuit. At this time, the PMOS transistor M R212 and NMOS transistor M R213 The switch combination outputs the reference voltage V REF At this time, the capacitive load provided by the bandpass selection capacitor in the bandpass filter is smaller, and the bandpass of the bandpass filter is higher compared to the above case 3.

[0089] The filter circuit corrects the swing of the output waveform by: The voltage-controlled oscillator of the CLASS-D structure outputs a common-mode voltage V CM , the output swing is 2V CM , the resonant output waveforms TANKP and TANKN are distorted. In addition to bandpass filtering the output signal, the filter circuit also controls the current limiting resistor R BIAS Under the action of, the common mode voltage of the output signals OUTP and OUTN is V CM2 , the output swing is V CM2 -V BIAS .

[0090] The current limiting resistor R BIAS Under the action of the output stage common mode voltage V CM2 and the resonant stage common mode voltage V CM Can be modulated separately:

[0091] V CM2 =Range2+V BIAS ;

[0092] Among them, Range2 is the output swing of the filter stage, V BIAS is the current limiting voltage on the current limiting control resistor;

[0093] Range2=(V BIAS / R BIAS / 2)×ro 34 ;

[0094] Among them, 34 For transistor M N3 and M N4 On-resistance;

[0095] After modulation, the common mode voltage of the output signals OUTP and OUTN is V CM2 , the output swing is V CM2 -V BIAS .

[0096] Figure 4 The waveform diagram of the resonant stage output signal and the adjustment diagram of the filter stage circuit on the output signal swing are given. The CLASS-D structure voltage-controlled oscillator outputs the common-mode voltage V CM , the output swing is 2V CM , the resonant output waveforms TANKP and TANKN are distorted, and the filter circuit swings to control the current limiting resistor R BIAS Under the action of, the common mode voltage of the output signals OUTP and OUTN is V CM2 , the output swing is V CM2 -V BIAS Before the swing correction, the swing is too large, and the resonant stage output waveform is distorted when the voltage drops below the ground voltage; after the swing correction, the output signal waveform is complete.

[0097] Figure 5 The schematic diagram of the bandpass filter frequency domain filtering is given. Through the bandpass selection module, the peak of the bandpass frequency domain appears at the frequency f of the resonant level output waveform. VCO Nearby, the bandpass filter has a positive gain for the signal at this frequency point and nearby. VCO The high-frequency noise and low-frequency jitter other than those in the embodiment of the present invention are suppressed, thereby enhancing the noise suppression performance of the differential cross-coupled voltage-controlled oscillator with the CLASS-D structure in the present invention.

[0098] It should be noted that the differential cross-coupled voltage-controlled oscillator with a CLASS-D structure provided in the above embodiment is only illustrated by the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the modules or steps in the embodiments of the present invention can be decomposed or combined. For example, the modules in the above embodiment can be combined into one module, or further divided into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are only for distinguishing the modules or steps, and are not regarded as improper limitations of the present invention.

[0099] The terms "first", "second", etc. are used to distinguish similar objects rather than to describe or indicate a particular order or sequence.

[0100] The term "comprise" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that includes a list of elements includes not only those elements but also other elements not expressly listed, or also includes elements inherent to such process, method, article, or apparatus / device.

[0101] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A differential cross-coupled voltage-controlled oscillator with a CLASS-D structure, the oscillator comprising a resonant stage module and a filter stage module, characterized in that: The resonance stage module and the filter stage module are connected by a DC isolation capacitor C m1 and C m2 connect; The resonant stage module is based on a CLASS-D structure and is used to generate an extremely low-noise oscillation signal, the frequency of which is adjusted by frequency band selection and a varactor diode; The filter stage module performs band-pass filtering and swing adjustment on the signal generated by the resonance stage module to restore the distorted waveform and output a pair of differential sine wave signals.

2. The differential cross-coupled voltage-controlled oscillator with a CLASS-D structure according to claim 1, characterized in that: The resonant stage module includes a filter circuit, a common mode voltage regulation circuit, a differential inductor L connected in sequence. TANK , band selection module, differential varactor circuit, cross-coupled transistor pair M N1 and M N2 .

3. The differential cross-coupled voltage-controlled oscillator of a CLASS-D structure according to claim 2, characterized in that: The frequency band selection module includes M frequency modulation units; The frequency modulation capacitance values ​​of the M frequency modulation units are geometric progression {C TANK , 2C TANK 、4C TANK , ..., 2 M-1 C TANK }; where M is the frequency modulation accuracy of the voltage controlled oscillator.

4. The differential cross-coupled voltage-controlled oscillator of a CLASS-D structure according to claim 3, characterized in that: Two frequency modulation capacitors C of the M frequency modulation units TANK One end is connected to the differential inductor L TANK The two arms TANKN and TANKP, the other end is connected in series with a series resistor R TANK11 and R TANK12 ; Series resistance R TANK11 and R TANK12 The two ends of the transistor switch M are connected across R11 The source and drain of the transistor switch M R11 、M R12 、M R13 The gate of the external input signal SW is connected CAP , transistor switch M R12 The source of the external input reference voltage V REF , transistor switch M R12 、M R13 The drain connected series resistor R TANK11 and R TANK12 The middle node of transistor switch M R13 The source is grounded.

5. The differential cross-coupled voltage-controlled oscillator with a CLASS-D structure according to claim 4, characterized in that: The frequency modulation unit, the method for adjusting the frequency of the voltage-controlled oscillator thereof comprises: When the external input signal SW CAP For high level signals, two FM capacitors C TANK The transistor switch M plays a capacitive role in the resonant stage of the voltage controlled oscillator. R11 On, series resistance R TANK11 and R TANK12 is short-circuited, transistor M R12 、M R13 The switch combination gives the series resistor R TANK11 and R TANK12 The middle node outputs a low level; When the external input signal SW CAP For low level signals, two FM capacitors C TANK The transistor switch M does not play a capacitive role in the resonant stage of the voltage controlled oscillator. R11 Disconnect, series resistor R TANK11 and R TANK12 Access circuit, transistor M R12 、M R13 The switch combination outputs the reference voltage V REF .

6. The differential cross-coupled voltage-controlled oscillator with a CLASS-D structure according to claim 4, characterized in that: The differential varactor circuit includes a varactor diode C var1 and C var2 , series resistance R var1 and R var2 , capacitor C a1 and C a2 ; Varactor diode C var1 and C var2 The two source / drain terminals are connected to the differential control voltage positive terminal V CP , the two gates are connected to capacitors C a1 and C a2 one end of Capacitor C a1 and C a2 The other end is connected to the differential inductor L TANK The two arms TANKN and TANKP; Series resistance R var1 and R var2 Connect a variable capacitance diode C across both ends of var1 and C var2 The two gates are connected in series with a resistor R var1 and R var2 The middle node is connected to the negative terminal of the differential control voltage V CN .

7. The differential cross-coupled voltage-controlled oscillator with a CLASS-D structure according to claim 6, characterized in that: The method for adjusting the frequency of the voltage-controlled oscillator of the differential varactor circuit includes: Differential inductance L TANK The common-mode voltage on the two arms TANKP and TANKN is equal, and the differential control voltage V CP and V CN Equivalent to varactor diode C var1 and C var2 The voltage difference between the two ends is ΔV = V CP -V CN Influence of varactor diode C var1 , C var2 Capacitance value; The larger the ΔV, the larger the capacitance of the varactor diode C var1 , C var2 The smaller the capacitance, the higher the voltage-controlled oscillator frequency; The smaller ΔV is, the smaller the capacitance of the variable capacitance diode C is. var1 , C var2 The larger the capacitance, the lower the voltage controlled oscillator frequency.

8. The differential cross-coupled voltage-controlled oscillator with a CLASS-D structure according to claim 1, characterized in that: The filter stage module includes a common mode voltage regulating resistor, a differential inductor L connected in sequence. BPF , bandpass selection module, bandpass filter resistor R BPF , transistor pair M N3 and M N4 , swing control current limiting resistor R BIAS .

9. The differential cross-coupled voltage-controlled oscillator with a CLASS-D structure according to claim 8, characterized in that: The bandpass selection module includes N bandpass selection units; The frequency modulation capacitance values ​​of the N bandpass selection units are a geometric progression {C BPF , 2C BPF 、4C BPF , ..., 2 N-1 C BPF }; where N is the adjustment accuracy of the filter passband.

10. The differential cross-coupled voltage-controlled oscillator with a CLASS-D structure according to claim 9, characterized in that: The filter stage module, the method for adjusting the amplitude of the output signal thereof comprises: The swing control current limiting resistor R BIAS Under the action of the output stage common mode voltage V CM2 and the resonant stage common mode voltage V CM Can be modulated separately: In CM2 =Range2+V BIAS ; Among them, Range2 is the output swing of the filter stage, V BIAS is the current limiting voltage on the current limiting control resistor; Range2=(V BIAS / R BIAS / 2)×ro 34 ; Among them, 34 For transistor M N3 and M N4 On-resistance; After modulation, the common mode voltage of the output signals OUTP and OUTN is V CM2 , the output swing is V CM2 -V BIAS .

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