CN203071909U

CN203071909U - Novel switch structure capable of optimizing phase noise performance of voltage controlled oscillator (VCO)

Info

Publication number: CN203071909U
Application number: CN 201320059918
Authority: CN
Inventors: 李国儒; 李云初; 戴惜时
Original assignee: Suzhou Yunchip Microelectronic Technology Co Ltd
Current assignee: Suzhou Yunchip Microelectronic Technology Co Ltd
Priority date: 2013-02-01
Filing date: 2013-02-01
Publication date: 2013-07-17
Anticipated expiration: 2023-02-01

Abstract

The utility model discloses a novel switch structure capable of optimizing the phase noise performance of a voltage controlled oscillator (VCO), which comprises three MOS switch tubes. The grid electrodes of the three MOS switch tubes are mutually connected and are also connected with a control voltage. The source electrodes of the second and third MOS switch tubes are grounded and the drain electrodes of the second and third MOS switch tubes are respectively connected with the source electrode and the drain electrode of the first MOS switch tube. The novel switch structure also comprises two MOS capacitance tubes. The grid electrodes of the two MOS capacitance tubes are respectively connected with the source electrode and the drain electrode of the first MOS switch tube. The source electrodes of the two MOS capacitance tubes are connected together and then are grounded. The drain electrodes of the two MOS capacitance tubes are grounded. According to the utility model, due to the adoption of a nonlinear capacitance compensating circuit, the influence of the non-linear parasitic capacitance of the switch on the phase noise of the VCO can be well compensated when the switch is switched off. Due to the adoption of the above improved structure, when the switch is totally switched off, the phase noise performance of the VCO can be well improved. Meanwhile, when the switch is totally switched on, the circuit of the VCO is hardly influenced by the switch. Therefore, the high-band phase noise performance of the VCO is greatly improved.

Description

A kind of novel switched structure of optimizing the VCO phase noise performance

Technical field

The utility model relates to a kind of high-performance radio-frequency phase-locked loop chip design, relates in particular to a kind of novel switched structure of the VCO of optimization phase noise performance, belongs to the semiconductor integrated circuit technical field.

Background technology

Phase-locked loop has a wide range of applications in various chip products as the local frequency synthesis module in clock frequency synthesis module or the radio frequency chip.Proposition along with the development of electronic industry and various new communication standard, people are more and more higher to the requirement of the integrated more multi-communication protocol of single-chip, and the difference of different communication protocol band occupancy means that phase-locked loop need have wideer frequency coverage when guaranteeing the good phases noiseproof feature.

Classical analog phase-locked look circuit module comprises: phase frequency detector (PFD), analog loop filter (LPF), voltage controlled oscillator (VCO), frequency divider etc.; Different with analog phase-locked look, digital phase-locked loop adopts TDC to substitute phase frequency detector, and digital filter substitutes analog filter, and digital controlled oscillator (DCO) substitutes voltage controlled oscillator (VCO).VCO or DCO, as the chief component of phase-locked loop, its phase noise performance directly influences the phase noise performance of whole phase-locked loop.In order to guarantee rational oscillator gain, the phase-locked loop of broadband coverage is often by adding the capacitance realization of more switches change resonant cavity, as shown in Figure 7 in oscillator in the phase-locked loop systems design.But the phase noise performance of the non-ideal characteristic of switch meeting severe exacerbation oscillator in the CMOS technology.

The switching circuit structure as shown in Figure 1 in the tradition broadband coverage VCO circuit.Switch is made up of three MOS switching tube M0, M1, M2, and ideally, when control voltage SW desirable conducting of switch when being high, capacitor C 0, C1 insert the resonant cavity two ends, increase the resonant cavity capacitance, and VCO vibrates in low-frequency range; Switch was desirable when voltage SW was low turn-offs when controlling, and capacitor C 0, C1 break away from resonant cavity, and VCO vibrates at high band.Yet, the equivalent electric circuit under actual metal-oxide-semiconductor switch conduction and the shutoff situation as shown in Figure 2, switch dead resistance Rds has a strong impact on the Q value of cavity of capacitor C 0 and C1 under the conducting situation, causes the low-frequency range phase noise to worsen.In order to reduce switch conduction to the influence of the Q value of cavity, need to strengthen switch size; Switch parasitic non-linear capacitance Cdg/Cdb (Csg/Csb) inserts in the resonant cavity under the shutoff situation, the VCO output signal of high frequency almost all enters into the two ends of nonlinear capacitance by capacitor C 0, C1, make the electric capacity in the resonant cavity constantly change along with the variation of oscillation amplitude, worsened the phase noise performance of VCO.Particularly when VCO was operated in highest frequency, the switch of all switching circuits all disconnected, and whole switching circuit shows as a very large nonlinear capacitance in resonant cavity, can have a strong impact on the phase noise performance of voltage controlled oscillator.Can be by reducing the influence that switch size reduces nonlinear capacitance, but the small size switch can have a strong impact on the phase noise performance of VCO low-frequency range again.As seen traditional construction of switch can not be taken into account height frequency range phase noise performance, particularly under the very high situation of VCO frequency coverage.

The utility model content

Technical problem to be solved in the utility model is the defective that overcomes prior art, and a kind of novel cmos switch structure is provided, and optimizes its high band phase noise performance when not influencing broadband coverage VCO low-frequency range phase noise performance.

For solving the problems of the technologies described above, the utility model provides a kind of novel switched structure of the VCO of optimization phase noise performance, comprises three grids connect altogether and be connected with control voltage SW a MOS switching tube, the 2nd MOS switching tube, the 3rd MOS switching tube; The source ground of described the 2nd MOS switching tube, the 3rd MOS switching tube, drain electrode is connected with drain electrode with the source electrode of a MOS switching tube respectively, it is characterized in that also comprise two mos capacitance pipes, the grid of two mos capacitance pipes is connected respectively to source electrode and the drain electrode of a described MOS switching tube; The source electrode of two mos capacitance pipes is connected to ground altogether; The equal ground connection of the drain electrode of two mos capacitance pipes.

The construction of switch that is connected and composed by above-mentioned each element is as a switching branches, and a plurality of described switching branches are in parallel to constitute switch arrays.

Described switch arrays adopt binary digit control bit or any other digital coding mode to control.

The beneficial effect that the utility model reaches:

The utility model adds the nonlinear capacitance compensating circuit on traditional VCO switching circuit architecture basics, well compensated the non-linear parasitic capacitance of switch when switch disconnects to the influence of VCO phase noise.By this improved switching circuit structure of analysis, and simulating, verifying, can see that this improvement structure phase noise performance to voltage controlled oscillator when switch all disconnects has good improvement, and when the whole conducting of switch, circuit almost not influenced.In the design of now voltage controlled oscillator, along with the rising of frequency, the widening of frequency coverage, the utility model will improve the high band phase noise performance of VCO greatly.

Description of drawings

Fig. 1 is traditional VCO construction of switch;

Fig. 2 is traditional VCO switch equivalent electric circuit;

Fig. 3 is novel VCO construction of switch of the present utility model;

Fig. 4 is the circuit model of novel VCO switching circuit of the present utility model;

Fig. 5 is the half of circuit model of novel VCO switching circuit of the present utility model;

The capacitance curve of Cd01 and Cg3 when Fig. 6 is the switch disconnection;

Fig. 7 is the VCO that adopts the traditional switch array structure;

Fig. 8 adopts the VCO of novel switched array structure;

Adopt the VCO phase noise curve of tradition and novel switched structure during the whole conducting of Fig. 9 switch;

When all disconnecting, adopts by Figure 10 switch the VCO phase noise curve of tradition and novel switched structure.

Embodiment

Below in conjunction with accompanying drawing the utility model is further described.Following examples only are used for the technical solution of the utility model more clearly is described, and can not limit protection range of the present utility model with this.

In the VCO of broadband coverage, can not take into account the defective of height frequency range phase noise performance simultaneously at the traditional switch structure, the utility model has provided a kind of new construction of switch, can optimize its high band phase noise performance when not influencing VCO low-frequency range phase noise performance.Circuit structure as shown in Figure 3, the grid end of MOS switching tube M0, M1, M2 connects altogether, and is connected with control voltage SW.The source end ground connection of MOS switching tube M1, M2, the drain terminal of MOS switching tube M1, M2 are connected with drain terminal with the source end of MOS switching tube M0 respectively.Simultaneously, the source end of MOS switching tube M0 is used for being connected with capacitor C 0, the C1 of VCO respectively with drain terminal.

Simultaneously, the source end of MOS switching tube M0 and drain terminal are connected the grid end of mos capacitance pipe M3, M4 respectively, and the source end of mos capacitance pipe M3, M4 connects and ground connection altogether, the equal ground connection of drain terminal of mos capacitance pipe M3, M4.

The circuit equivalent model of construction of switch of the present utility model as shown in Figure 4.Cd01 and Cs01 are respectively MOS switching tube M0, the direct-to-ground capacitance of M1 pipe and the MOS switching tube M0 that sees from MOS switching tube M0 source end that sees from MOS switching tube M0 drain terminal, the direct-to-ground capacitance of M2 pipe, Cg3, Cg4 are respectively the direct-to-ground capacitance of seeing from mos capacitance pipe M3, M4 pipe grid end, and Rds is the source ohmic leakage of MOS switching tube M0.Under the situation of parameters of switching size, during switch conduction, can guarantee that source ohmic leakage Rds is a very little resistance, the parasitic capacitance at ohmic leakage Rds two ends, source can be ignored influence circuit, although so compare the parasitic capacitance that new circuit structure has increased mos capacitance pipe M3/M4 grid ends with the traditional switch structure, the influence of this parasitic capacitance can be ignored fully under low frequency.When switch disconnected, source ohmic leakage Rds was a very large resistance, and high-frequency signal directly is added in the two ends of non-linear parasitic capacitance by capacitor C 0/C1.In order to be illustrated more clearly in novel switched structure to the effect of electric capacity compensation of nonlinearity, the half of equivalent-circuit model of novel switching circuit as shown in Figure 5 when switch turn-offed.When the drain terminal of MOS switching tube M0 had the voltage Vd of a variation, this voltage directly was added in drain terminal and the mos capacitance pipe M3 grid end of MOS switching tube M0, M1, and equivalent parasitic capacitances Cd01, Cg3 will change along with the variation of voltage Vd.These two electric capacity are separately seen with the variation of voltage Vd: MOS switching tube M0, M1 grid end ground connection, Cd01 is equivalent to along with active area drain terminal voltage Vd is changing; And ground is missed in mos capacitance pipe M3 source, and Cg3 is equivalent to along with grid terminal voltage V _dChanging, this can equivalence be mos capacitance pipe M3 grid end ground connection, and Cg3 is equivalent to along with active area source drain terminal voltage (V _d) changing.That is to say that Cd01, Cg3 will change along with the opposite tendency that is varied to of MOS switching tube M0 drain terminal voltage Vd.Because of this opposite variation tendency, the parasitic capacitance of seeing from MOS switching tube M0 drain terminal over the ground is that Cd01, Cg3 addition electric capacity in parallel will present the variation that relatively relaxes along with the variation of MOS switching tube M0 drain terminal voltage Vd, circuit structure in Fig. 1, the adding of mos capacitance pipe M3 has well compensated the degree of Cd01 with MOS switching tube M0 drain terminal change in voltage.Reasonably mos capacitance pipe M3/M4 size Selection will can be good at the non-linear parasitic capacitance of compensating switch, has optimized the phase noise performance of VCO at high band.As seen, novel switched structure can have been taken into account the height frequency range phase noise performance of broadband coverage VCO preferably.

Fig. 6 is under the certain size, and when switch disconnected, Cd01 and Cg3 were with the capacitance curve of MOS switching tube M0 drain terminal change in voltage.We can see clearly that Cd01 and Cg3 become opposite variation tendency on the whole with the variation of MOS switching tube M0 drain terminal voltage Vd from Fig. 6, under rational size Selection, mos capacitance pipe M3/M4 will can be good at compensating the non-linear parasitic capacitance of traditional switch structure with the intensity of variation of voltage.

Fig. 7, Fig. 8 adopt the VCO circuit of conventional switch circuit structure and the VCO circuit of novel switched circuit structure.Two VCO circuit main parts are the same: the top current sources biasing, and difference PMOS pipe forms negative resistance to the compensating circuit loss, and MOS capacitive reactance pipe realization control voltage is tuning to frequency, and switching circuit portion adopts 8 bit-binary numeral control bit to control.Difference is the switching circuit difference, and fixed capacity Cfix distinguishes to some extent simultaneously, guarantees two VCO operating frequency unanimities.Two VCO carry out phase noise emulation, simulation result such as Fig. 9, shown in Figure 10 during to the whole conductings of switch and whole the disconnection.Can see that to the almost not influence of phase noise of VCO, the VCO phase noise curve of traditional switch structure and novel switched structure almost coincides together novel switched circuit among Fig. 9 when the whole conducting of switch.When switch all disconnects, adopt the phase noise of the VCO of novel switched structure obviously to be better than the VCO of traditional switch structure, solid line is the phase noise curve of the VCO of novel switched structure among Figure 10, dotted line is the phase noise curve of the VCO of traditional switch structure.Further illustrate novel switched structure and when not influencing broadband coverage VCO low-frequency range phase noise performance, optimize its high band phase noise performance.

The above only is preferred implementation of the present utility model; should be understood that; for those skilled in the art; under the prerequisite that does not break away from the utility model know-why; can also make some improvement and distortion, these improvement and distortion also should be considered as protection range of the present utility model.

Claims

1. the novel switched structure that can optimize the VCO phase noise performance comprises three grids connect altogether and be connected with control voltage a MOS switching tube, the 2nd MOS switching tube, the 3rd MOS switching tube; The source ground of described the 2nd MOS switching tube, the 3rd MOS switching tube, drain electrode is connected with drain electrode with the source electrode of a MOS switching tube respectively, it is characterized in that also comprise two mos capacitance pipes, the grid of two mos capacitance pipes is connected respectively to source electrode and the drain electrode of a described MOS switching tube; The source electrode of two mos capacitance pipes is connected to ground altogether; The equal ground connection of the drain electrode of two mos capacitance pipes.

2. the novel switched structure of optimizing the VCO phase noise performance according to claim 1 is characterized in that, the construction of switch that is connected and composed by above-mentioned each element is as a switching branches, and a plurality of described switching branches are in parallel to constitute switch arrays.