CN100459417C

CN100459417C - Differential amplifier in low voltage and low power consumption and high isolation

Info

Publication number: CN100459417C
Application number: CNB2005100119276A
Authority: CN
Inventors: 宋睿丰; 廖怀林; 张国艳
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2005-06-14
Filing date: 2005-06-14
Publication date: 2009-02-04
Anticipated expiration: 2025-06-14
Also published as: CN1697312A

Abstract

Two MOSFETs connected in common source mode are as input ends of the differential signal of amplifier. Resistance, inductance or other active device is adopted as load as well as feedback element at source end of amplifier or trail current source. Two MOSFETs identical to two input MOSFETs in common source mode are added. Gate end of one MOSFET is connected to gate end of input MOSFET for inputting positive signal; and drain end is connected to drain end of input MOSFET for inputting negative signal (negative output end). Gate end of the other MOSFET is connected to gate end of input MOSFET for inputting negative signal; and drain end is connected to drain end of input MOSFET for inputting positive signal (positive output end). The invention takes full advantage of identical gate-drain capacitances of MOSFET parts operated at saturation region and cutoff region. Features are: low voltage, low power consumption and high degree of reverse isolation.

Description

Differential amplifier in low voltage and low power consumption and high isolation

Technical field

The invention belongs to the low-voltage and low-power dissipation CMOS RFIC applied technical field in deep-submicron epoch, be particularly useful for the low noise amplifier (LNA) in the radio-frequency (RF) CMOS integrated circuit (RFIC).

Background technology

Along with the cmos vlsi technology entered for 65 eras of nanotechnology, serious short-channel effect (short channel effect) appears in the field-effect transistor in the circuit, showing as threshold voltage (threshold voltage) reduces with channel length and descends, threshold voltage increases with drain terminal voltage and descends, and the device intrinsic output resistance reduction that the long mudulation effect of direct break-through (punch-through) ditch causes etc. is leaked in the source.The second-order effects of the caused device of short-channel effect causes circuit malfunction easily.Therefore the inhibition of short-channel effect is the urgent problem that improves the cmos vlsi circuit performance and reduce circuit malfunction.

The operating voltage of device also constantly reduces thereupon in device dimensions shrink, therefore requires supply voltage in the circuit must not surpass the maximum working voltage of device.In the radio circuit design process, should reduce supply voltage as much as possible to satisfy the job requirement of device.

Low noise amplifier is one of requisite composition module of institute in the radio-frequency transmitter.According to the Friis formula as can be known, as the first order in the whole receiver composition module, the noise factor of amplifier has determined the noise factor of whole receiver.Therefore in the process of design amplifier, should reduce its noise factor as far as possible to improve the noiseproof feature of whole system.Simultaneously as the module that links to each other with frequency mixer with antenna, amplifier also must have higher reverse isolation performance and reduce local oscillation signal by the leakage of antenna to the external world.Especially for direct conversion receiver, because local oscillation signal is identical with the frequency of received signal, so this problem is even more important.Usually in the Design of Amplifier process, in order to improve its stability and reverse isolation performance, the structure of the amplifier of normal employing is a cascodes, as shown in Figure 1.This structure makes that by introducing second device the impedance between two metal-oxide-semiconductors is Thereby reduced because C _GdThe Miller effect that produces has improved the reverse isolation ability of circuit, especially the LO of frequency mixer is subsequently leaked.Because having improved the output impedance of LNA, this structure (is about original g simultaneously _M2r _O2Times), thereby also help the raising that whole amplifier gains.Though solved isolating problem still, because the metal-oxide-semiconductor of introducing has also produced other problem more.At first, needing more voltage remaining, make the operating voltage of circuit be difficult to drop to below 1 volt, is not to be well suited for low-voltage and low-power dissipation to use; Secondly, introduced extra noise source (grid metal-oxide-semiconductor altogether), though under low frequency, can ignore by these noises of grid metal-oxide-semiconductor introducing altogether, along with the rising of frequency, impedance between two metal-oxide-semiconductors makes and can not ignore from the noise of MG because the effect of parasitic capacitance reduces rapidly.Though can produce resonance by parasitic capacitance at the source of MG end shunt inductance and this place, to increase its resistance value, improve noiseproof feature, this can increase the area of whole module on the one hand, also can introduce the complexity of extra parasitism and circuit simultaneously.The folded common source and common grid structure is the amplifier (as shown in Figure 2) of another cascodes, because the method that has adopted PMOS and NMOS to combine, make that supply voltage can be less than traditional cascodes, yet the use of folded common source and common grid structure but has been subjected to considerable restraint in the reality.This mainly is because be difficult to obtain the LC resonant network of high-quality-factor in the design of CMOS integrated circuit, make the LC resonant network practical impedance with

Can compare, make the RF signal produce shunting, therefore the signal of a part has been lost in the LC resonant network, so the gain of folded common source and common grid structure is less than traditional cascodes usually.

Thomas H.Lee has reported that a kind of mode that adopts in the cross coupling capacitor and change improves the structure of isolation between the differential amplifier input/output terminal, as shown in Figure 3.This structural requirement capacitor C _NThe grid leak parasitic capacitance of source capsule is accurately mated to realize the neutralization between the input/output signal together.Yet because the grid leak parasitic capacitance of common source pipe changes with the drain-to-gate voltage of its input usually, this makes capacitor C _NThe accurate coupling of grid leak parasitic capacitance of source capsule is difficult to realize usually together.Therefore the application of this structure is very limited usually in actual Design of Amplifier.

As the simplest common source type differential amplifier (as shown in Figure 4) of structure, this amplifier adopts the input of two MOSFET that connect in the common source mode as two differential signals, adopt resistance, inductance or other active device as load, adopt resistance, inductance or other active device as amplifier source end feedback element or tail current source.This structure has low-down operating voltage, owing to used minimum device to realize the low noise enlarging function, its noise factor also can be low than the amplifier of other structure simultaneously, is a kind of structure with fine application potential therefore.But owing to only adopted the isolation effect between its input/output terminal of single tube can be because the Miller effect non-constant that becomes, so in actual application, have limited the range of application of this structure.Especially the application under high frequency is difficult especially, because this can make the stability of circuit produce very big problem.

Summary of the invention

The purpose of this invention is to provide a kind of differential amplifier with low-voltage and low-power dissipation, high reverse isolation degree.

Technology contents of the present invention: a kind of differential amplifier in low voltage and low power consumption and high isolation, the input of differential signal is two mos field effect transistor MOSFET that connect in the common source mode, adopt resistance, inductance or other active device are as load, resistance, inductance or other active device are as amplifier source end feedback element or tail current source, it is characterized in that: increase by two and the identical MOSFET of common source input MOSFET, the MOSFET of these two increases is operated in cut-off region, the grid end of one of them MOSFET links to each other with the grid end of the common source MOSFET of input positive signal, the common source MOSFET drain terminal link to each other (negative output terminal) of the drain terminal of this MOSFET and input negative signal, the grid end of another MOSFET links to each other with the grid end of common source MOSFET of input negative signal, the drain terminal of this MOSFET with import positive signal common source MOSFET drain terminal link to each other (positive output end).

The source end of two MOSFET that increase can be connected with each other, also can be unsettled.

Technique effect of the present invention: because the deep sub-micro MOSFET device is during in the saturation region with at cut-off region, the grid leak mutual capacitance of device is identical, make full use of this characteristics, identical by increasing by two with common source input MOSFET, be operated in the MOSFET of cut-off region and employing cross-connection system, a kind of novel differential amplifier with low-voltage and low-power dissipation, high reverse isolation degree is provided.Compare with traditional differential common source type amplifier, this circuit structure can be worked under low-voltage at the assurance amplifier, realize the high isolation between input and the output simultaneously, effectively reduce the supply voltage and the power consumption of entire circuit, make it to be suitable for the application of amplifier in low pressure, the low-power consumption wireless radiofrequency receiver.

Compare with the amplifier of traditional common source type differential configuration, the present invention has guaranteed the reverse isolation performance of amplifier under the constant substantially prerequisite of overall performance, effectively improve the reverse isolation performance of entire circuit, make it to be suitable for the application of amplifier in low pressure, the low-power consumption wireless radiofrequency receiver.

The present invention compares with the amplifier that adopts electric capacity neutralization (Neutralization), owing to utilize with input MOSFET same size and be operated in the parasitic gate leakage capacitance coupling of parasitic capacitance that the MOSFET grid leak utmost point of cut-off region produced and input MOSFET, therefore do not imported the influence of gate voltage, had very strong application prospect.

Description of drawings

Below in conjunction with accompanying drawing, the present invention is made detailed description.

Fig. 1 is a traditional classical type common source and common grid amplifier structural representation;

Fig. 2 is the folded common source and common grid amplifier structural representation;

Fig. 3 adopts the capacity neutralization method to improve the structural representation that the amplifier input/output port is isolated;

Fig. 4 is the electrical block diagram of traditional common source type differential amplifier;

Fig. 5 is the electrical block diagram of differential amplifier in low voltage and low power consumption and high isolation of the present invention;

Fig. 6 is that the S12 parameters simulation result that two kinds of structure amplifiers carry out compares.

Embodiment

Differential amplifier in low voltage and low power consumption and high isolation of the present invention adopts the input of two MOSFET that connect in the common source mode as two differential signals, adopt resistance, inductance or other active device as load, adopt resistance, inductance or other active device as amplifier source end feedback element or tail current source; Adopt two and the identical MOSFET of input MOSFET simultaneously, the source end of these two MOSFET is connected with each other or is unsettled, the grid end of one of them MOSFET links to each other with the grid end of the common source MOSFET of input positive signal, the common source MOSFET drain terminal link to each other (negative output terminal) of the drain terminal of this MOSFET and input negative signal, the grid end of another MOSFET links to each other with the grid end of the common source MOSFET of input negative signal, the drain terminal of this MOSFET with the input positive signal common source MOSFET drain terminal link to each other (positive output end), be the intersection connected mode.The load of whole differential amplifier can be adopted inductance, electric capacity, resistance, active device etc. according to the difference of application background, or the combination between them; The source end of input MOSFET can adopt inductance, electric capacity, resistance, active device etc. to form feedback or tail current source.

Electrical block diagram of the present invention as shown in Figure 5, by among Fig. 5 as can be seen, comprise four identical MOSFET, be respectively M1, M2, M3, M4, the input of differential signal is M1 and M4, M2, M3 are the MOSFET that is operated in cut-off region and adopts cross-connection system because adopted M2, M3 to realize to import and output signal between cancel out each other, thereby reached the characteristics that realize high-isolation.And the MOSFET that adopts the cross-couplings mode to connect is in cut-off state, therefore also can not produce quiescent dissipation.

The present invention has following characteristics:

1, because the circuit of differential configuration has the ability of stronger inhibition common-mode signal, help the raising of circuit performance, so the form of difference is normally adopted in the input of radiofrequency signal in the modern radio-frequency wireless telecommunications.

2, because the grid of M1 and M2, M3 and M4 interconnects.Be operated in the strong inversion state under and be operated in that its gate leakage capacitance equates principle as can be known under the cut-off state according to short ditch device, the gate leakage capacitance of the M1-M4 device of being seen into by device grid end is equal fully at this moment.The parasitic capacitance Cgd that therefore can guarantee input pipe M1 and M4 with mate fully by the building-out capacitor Cgd1 that M2 and M3 produced, do not imported the influence that grid voltage changes.

3, the big or small same phase owing to two input signal RF+ and RF-signal is opposite, therefore when M2 and M3 employing mode as shown in Figure 4 are connected, because therefore 180 ° of the phase phasic differences of the signal of difference output end can cancel out each other output to the signal of input feedthrough.

4, owing to adopted said method, so circuit is under the degree of isolation that realizes between the identical input/output port, and structure that the present invention adopts can not used common bank tube.Thereby reduced the stacking of one deck metal-oxide-semiconductor, made supply voltage can reduce an overdrive voltage (about 0.2---0.3V) at least.Therefore under the constant prerequisite of current drain, can effectively reduce the power consumption of whole amplifier.

Low voltage and low power consumption and high isolation amplifier of the present invention is compared with the common source type differential amplifier:

The operating frequency of two amplifiers is 5.0GHz, and the input coupling adopts classical inductive source feedback system.The technology that adopts is Jazz BC35 standard CMOS process, and its minimum feature size is 0.35um, and the threshold voltage of employed MOSFET is 0.58V, and the employed supply voltage of circuit is 0.8V, whole amplifier and current drain be 4mA.

The S12 parameters simulation result of Fig. 6 for adopting Cadence Spectra RF simulation software that two kinds of structure amplifiers are carried out.Wherein abscissa is represented frequency, and ordinate is represented the reverse isolation degree (S21) of amplifier, the reverse isolation degree of the traditional common source type differential amplifier of curve 1 expression, and curve 2 is for adopting the reverse isolation degree of amplifier proposed by the invention.By simulation result among Fig. 6 more as can be seen, adopt the reverse isolation degree of the amplifier of this structure to be significantly improved (more than the 20dB), the reverse isolation performance of its degree of isolation and traditional cascade type amplifier is suitable.

Claims

1, a kind of differential amplifier in low voltage and low power consumption and high isolation, the input of differential signal is two mos field effect transistor MOSFET that connect in the common source mode, adopt resistance, inductance or other active device are as load, resistance, inductance or other active device are as amplifier source end feedback element or tail current source, it is characterized in that: increase by two and the identical MOSFET of common source input MOSFET, the MOSFET of these two increases is operated in cut-off region, the grid end of one of them MOSFET links to each other with the grid end of the common source MOSFET of input positive signal, the drain terminal of this MOSFET links to each other with the common source MOSFET drain terminal of input negative signal, the grid end of another MOSFET links to each other with the grid end of common source MOSFET of input negative signal, the drain terminal of this MOSFET with import positive signal common source MOSFET drain terminal link to each other.

2, differential amplifier in low voltage and low power consumption and high isolation as claimed in claim 1 is characterized in that: the source end of two MOSFET of increase is connected with each other.

3, differential amplifier in low voltage and low power consumption and high isolation as claimed in claim 1 is characterized in that: the source end of two MOSFET of increase is unsettled.