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

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

Low Voltage Low Power High Isolation Differential Amplifier

technical field

The invention belongs to the field of low-voltage and low-power CMOS RFIC application technology in the deep submicron era, and is especially suitable for low-noise amplifiers (LNAs) in radio frequency CMOS integrated circuits (RFICs).

Background technique

As CMOS VLSI technology enters the era of 65nm technology, the field effect transistor in the circuit has a serious short channel effect, which is manifested as the threshold voltage (threshold voltage) decreases with the decrease of the channel length. The threshold voltage decreases with the increase of the drain terminal voltage, and the intrinsic output resistance of the device is reduced due to the direct source-drain punch-through (punch-through) channel length modulation effect. The second-order effect of the device caused by the short channel effect is easy to cause circuit failure. Therefore, the suppression of short-channel effects is an urgent problem to be solved to improve the performance of CMOS VLSI circuits and reduce circuit failure.

As the size of the device shrinks, the operating voltage of the device is also continuously reduced. Therefore, it is required that the power supply voltage in the circuit must not exceed the maximum operating voltage of the device. In the process of RF circuit design, the power supply voltage should be reduced as much as possible to meet the working requirements of the device.

可比拟，使得RF信号产生分流，一部分的信号因此而损失在了LC谐振网络中，所以折叠共源共栅结构的增益通常要小于传统的共源共栅结构。A low noise amplifier is one of the essential building blocks in a radio frequency receiver. According to the Friis formula, as the first stage in the whole receiver module, the noise figure of the amplifier determines the noise figure of the whole receiver. Therefore, in the process of designing the amplifier, its noise figure should be reduced as much as possible to improve the noise performance of the whole system. At the same time, as a module connected to the antenna and the mixer, the amplifier must also have high reverse isolation performance to reduce the leakage of the local oscillator signal to the outside through the antenna. This is especially important for direct conversion receivers, since the local oscillator signal is at the same frequency as the received signal. Usually in the design process of the amplifier, in order to improve its stability and reverse isolation performance, the structure of the most commonly used amplifier is a cascode structure, as shown in Figure 1. In this structure, by introducing a second device, the impedance between the two MOS tubes is Thus reducing the Miller effect due to C _gd and improving the reverse isolation capability of the circuit, especially the LO leakage of the subsequent mixer. At the same time, because this structure improves the output impedance of the LNA (about the original g _m2 r _o2 times), it is also conducive to the improvement of the overall amplifier gain. Although the isolation problem has been solved, other problems have also arisen due to the introduction of multiple MOS tubes. First of all, more voltage margin is needed, making it difficult for the operating voltage of the circuit to drop below 1 volt, which is not very suitable for low-voltage and low-power applications; secondly, an additional noise source (common-gate MOS transistor) is introduced, although in These noises introduced by common gate MOS transistors can be ignored at low frequencies, but as the frequency increases, the impedance between the two MOS transistors decreases rapidly due to the effect of parasitic capacitance, so that the noise from MG cannot be ignored. Although it is possible to resonate with the parasitic capacitance at the source end of the MG by connecting an inductance in parallel to increase its impedance value and improve the noise performance, but this will increase the area of the entire module and introduce additional parasitic and circuit effects. Complexity. The folded cascode structure is another cascode structure amplifier (as shown in Figure 2). Due to the combination of PMOS and NMOS, the power supply voltage can be lower than the traditional cascode structure. However, In practice, the use of the folded cascode structure is greatly limited. This is mainly because it is difficult to obtain an LC resonant network with a high quality factor in the design of a CMOS integrated circuit, so that the actual impedance of the LC resonant network is different from that of

It can be compared that the RF signal is shunted, and a part of the signal is lost in the LC resonant network, so the gain of the folded cascode structure is usually smaller than that of the traditional cascode structure.

Thomas H.Lee reported a structure that uses cross-coupling capacitor neutralization to improve the isolation between the input and output terminals of the differential amplifier, as shown in Figure 3. This structure requires the capacitor C _N to accurately match the gate-drain parasitic capacitance of the common source transistor to achieve neutralization between the input and output signals. However, since the gate-drain parasitic capacitance of the common-source transistor usually varies with the input gate-drain voltage, it is usually difficult to achieve accurate matching between the capacitance C _N and the gate-drain parasitic capacitance of the common-source transistor. Therefore, the application of this structure in the design of practical amplifiers is usually very limited.

As the simplest common-source differential amplifier (as shown in Figure 4), the amplifier uses two common-source connected MOSFETs as the input terminals of the two differential signals, and uses resistors, inductors or other active devices as the load , using resistors, inductors or other active devices as amplifier source feedback elements or tail current sources. This structure has a very low operating voltage, and because it uses the least number of devices to realize the low-noise amplification function, its noise figure is also lower than that of amplifiers with other structures, so it is a structure with good application potential. However, because only a single tube is used, the isolation effect between the input and output terminals will become very poor due to the Miller effect, so the application range of this structure is limited in the actual application process. Especially the application at high frequency is more difficult, because this will make the stability of the circuit a big problem.

Contents of the invention

The purpose of the present invention is to provide a differential amplifier with low voltage, low power consumption and high reverse isolation.

Technical content of the present invention: a low-voltage, low-power consumption, and high-isolation differential amplifier. The input terminals of the differential signal are two metal-oxide-semiconductor field-effect transistors MOSFETs connected in a common source mode, and resistors, inductors, or other active devices are used. As a load, resistors, inductors or other active devices are used as amplifier source feedback elements or tail current sources, which are characterized by: adding two MOSFETs that are identical to the common source input MOSFET, and these two added MOSFETs work in the cut-off region, where The gate terminal of one MOSFET is connected to the gate terminal of the common source MOSFET that inputs the positive signal, the drain terminal of the MOSFET is connected to the drain terminal of the common source MOSFET that inputs the negative signal (negative output terminal), and the gate terminal of the other MOSFET is connected to the input negative signal The gate terminal of the common source MOSFET is connected, and the drain terminal of the MOSFET is connected with the drain terminal of the common source MOSFET inputting the positive signal (positive output terminal).

The sources of the added two MOSFETs can be connected to each other or suspended.

Technical effects of the present invention: Since the deep submicron MOSFET device has the same gate-to-drain working capacitance when it is in the saturation region and the cut-off region, this feature is fully utilized, and by adding two MOSFETs that are identical to the common-source input MOSFET, they work in the cut-off region Furthermore, the cross-connected MOSFET is used to provide a new type of differential amplifier with low voltage, low power consumption and high reverse isolation. Compared with traditional differential common-source amplifiers, this circuit structure can ensure that the amplifier works at low voltage while achieving high isolation between the input and output terminals, effectively reducing the power supply voltage and power consumption of the entire circuit, making it Suitable for amplifier applications in low-voltage, low-power RF wireless receivers.

Compared with the traditional common-source differential structure amplifier, the invention ensures the reverse isolation performance of the amplifier under the premise that the overall performance is basically unchanged, effectively improves the reverse isolation performance of the entire circuit, and makes it suitable for low voltage, low Applications of power amplifiers in radio frequency wireless receivers.

Compared with the neutralization (Neutralization) amplifier using capacitance, the present invention uses the same size as the input MOSFET and the parasitic capacitance generated by the MOSFET gate-drain working in the cut-off region matches the parasitic gate-drain capacitance of the input MOSFET, so It is not affected by the input gate voltage and has strong application prospects.

Description of drawings

The present invention will be described in detail below in conjunction with the accompanying drawings.

Figure 1 is a schematic diagram of the structure of a traditional classic cascode amplifier;

Fig. 2 is a structural schematic diagram of a folded cascode amplifier;

Fig. 3 is a structural schematic diagram of improving the isolation of the input and output ports of the amplifier by using the capacitance neutralization method;

FIG. 4 is a schematic diagram of a circuit structure of a conventional common-source differential amplifier;

5 is a schematic diagram of a circuit structure of a low-voltage, low-power, high-isolation differential amplifier of the present invention;

Figure 6 is a comparison of the S12 parameter simulation results of the amplifiers with two structures.

Detailed ways

The low-voltage, low-power, high-isolation differential amplifier of the present invention uses two MOSFETs connected in a common source mode as the input terminals of two differential signals, uses resistors, inductors or other active devices as loads, and uses resistors, inductors or other active The device is used as the feedback element or tail current source of the amplifier source; at the same time, two MOSFETs that are identical to the input MOSFET are used. The gate terminal of the MOSFET is connected to the drain terminal of the common-source MOSFET that inputs the negative signal (negative output terminal), and the gate terminal of the other MOSFET is connected to the gate terminal of the common-source MOSFET that inputs the negative signal. The drain terminal of the MOSFET The terminal is connected to the drain terminal of the common source MOSFET that inputs the positive signal (positive output terminal) in a cross-connection manner. The load of the entire differential amplifier can use inductors, capacitors, resistors, active devices, etc., or a combination of them according to different application backgrounds; the source of the input MOSFET can use inductors, capacitors, resistors, active devices, etc. to form feedback or tail current source.

The schematic diagram of the circuit structure of the present invention is shown in Figure 5, as can be seen from Figure 5, including four identical MOSFETs, respectively M1, M2, M3, M4, the input terminals of the differential signal are M1 and M4, M2, M3 For MOSFETs that work in the cut-off region and adopt cross-connection, M2 and M3 are used to cancel each other between the input and output signals, thus achieving the characteristics of high isolation. And the MOSFETs connected in the cross-coupling mode are in the cut-off state, so no static power consumption will be generated.

The present invention has following characteristics:

1. Because the circuit with differential structure has a strong ability to suppress common-mode signals, which is conducive to the improvement of circuit performance, the input of radio frequency signals in modern radio frequency wireless communication is usually in the form of differential.

2. Because the gates of M1 and M2, M3 and M4 are connected to each other. According to the principle that the gate-drain capacitance of the short-channel device is equal when it works in the strong inversion state and in the cut-off state, at this time, the gate-drain capacitance of the M1-M4 device viewed from the gate terminal of the device is completely equal. Therefore, it can be ensured that the parasitic capacitance Cgd of the input transistors M1 and M4 completely matches the compensation capacitance Cgd1 generated by M2 and M3, and is not affected by changes in the input gate voltage.

3. Since the two input signals RF+ and RF- have the same magnitude and opposite phases, when M2 and M3 are connected as shown in Figure 4, since the phase difference of the signals at the differential output terminals is 180°, the output The signals fed through from the end to the input cancel each other out.

4. Due to the adoption of the above method, the structure adopted in the present invention may not use a common gate tube when the circuit achieves the same degree of isolation between input and output ports. Therefore, the stacking of one layer of MOS tubes is reduced, so that the power supply voltage can be reduced by at least one overdrive voltage (about 0.2---0.3V). Therefore, the power consumption of the entire amplifier can be effectively reduced under the premise that the current consumption remains unchanged.

Comparing the present invention's low-voltage, low-power consumption, high-isolation amplifier with a common-source differential amplifier:

The operating frequency of the two amplifiers is 5.0GHz, and the input matching adopts the classic inductive source feedback method. The process used is the Jazz BC35 standard CMOS process, the minimum feature size is 0.35um, the threshold voltage of the MOSFET used is 0.58V, the power supply voltage used in the line is 0.8V, and the current consumption of the entire amplifier is 4mA.

Figure 6 shows the S12 parameter simulation results of the two structure amplifiers using Cadence Spectra RF simulation software. Wherein the abscissa represents the frequency, the ordinate represents the reverse isolation (S21) of the amplifier, the curve 1 represents the reverse isolation of the traditional common-source differential amplifier, and the curve 2 is the reverse isolation of the amplifier proposed by the present invention. From the comparison of the simulation results in Figure 6, it can be seen that the reverse isolation of the amplifier with this structure has been significantly improved (more than 20dB), and its isolation is comparable to that of the traditional cascode amplifier. .

Claims (3)

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.

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