A folded cascode mixer

Abstract

The present invention discloses a folded common-source and common-gate mixer, the mixer comprising: a transconductance amplifier, a differential common-gate amplifier, and a Gilbert mixer; the transconductance amplifier is connected to the differential common-gate amplifier, the differential common-gate amplifier is connected to the Gilbert mixer, and the transconductance amplifier is connected to the Gilbert mixer; wherein the transconductance amplifier is used for voltage-to-current conversion, the differential common-gate amplifier is used for absorbing the AC output current of the transconductance amplifier, and the Gilbert mixer is used for mixing; the transconductance amplifier receives a TXI signal, the Gilbert mixer receives an LO signal, and mixes the TXI signal with the LO signal and then outputs it. The present invention can reduce LO feedthrough and improve linearity performance.

Description

Technical Field

[0001] The present invention relates to the field of mixers, and in particular to a folded cascode mixer. Background Art

[0002] In recent years, with the rapid development of the communications industry, people have higher and higher performance requirements for wireless transceivers. Since the mixer is a nonlinear system, the signal will undergo gain compression after passing through the mixer, which may also cause the RF signal to be blocked, and it will also generate unnecessary frequency components, interfering with the useful signal and causing distortion, so linearity is a very important indicator. However, since the DC bias of the mixer will be affected by changes in the power supply voltage, process changes, and temperature changes, the instability of the bias circuit will affect the linearity of the mixer.

[0003] The conventional Gilbert mixer adopts the conventional source / emitter negative feedback, which has insufficient linearity and usually has the phenomenon of LO feedthrough. Therefore, there is an urgent need for a mixer that reduces LO feedthrough and improves linearity performance. Summary of the invention

[0004] In order to solve the above problems, an object of the present invention is to provide a folded cascode mixer, which can reduce LO feedthrough and improve linearity performance.

[0005] Based on this, the present invention provides a folded cascode mixer, the mixer comprising:

[0006] Transconductance amplifier, differential common-gate amplifier, Gilbert mixer;

[0007] The transconductance amplifier is connected to the differential common-gate amplifier, the differential common-gate amplifier is connected to the Gilbert mixer, and the transconductance amplifier is connected to the Gilbert mixer; wherein the transconductance amplifier is used for voltage-to-current conversion, the differential common-gate amplifier is used for absorbing the AC output current of the transconductance amplifier, and the Gilbert mixer is used for mixing;

[0008] The transconductance amplifier receives a TXI signal, and the Gilbert mixer receives an LO signal and mixes the TXI signal with the LO signal and outputs the mixed signals.

[0009] Wherein, the transconductance amplifier comprises:

[0010] A first MOS tube, a second MOS tube, a third MOS tube, a fourth MOS tube and a fifth MOS tube, a first resistor, a second resistor, a first capacitor and a second capacitor;

[0011] The source of the first MOS tube is connected to the power supply end, the gate is connected to the first power supply end, the drain is respectively connected to the sources of the second MOS tube and the third MOS tube, the drain of the second MOS tube is connected to the drain of the fourth MOS tube, the drain of the third MOS tube is connected to the drain of the fifth MOS tube, the gate of the second MOS tube is connected to the gate of the fourth MOS tube, the gate of the third MOS tube is connected to the gate of the fifth MOS tube, the first resistor is connected between the drain and the gate of the second MOS tube, the second resistor is connected between the drain and the gate of the third MOS tube, one end of the first capacitor is connected to the external TXI+ end, and the other end is connected to the gate of the second MOS tube, one end of the second capacitor is connected to the external TXI- end, and the other end is connected to the gate of the third MOS tube, and the sources of the fourth MOS tube and the fifth MOS tube are both grounded.

[0012] Wherein, the Gilbert mixer comprises:

[0013] Inductor, variable capacitor, sixth MOS tube, seventh MOS tube, eighth MOS tube, ninth MOS tube;

[0014] After the inductor is connected in parallel with the variable capacitor, one end is connected to the drain of the sixth MOS tube, and the other end is connected to the drain of the ninth MOS tube;

[0015] The gate of the sixth MOS tube is connected to the external LO+ terminal, the source of the sixth MOS tube and the source of the seventh MOS tube are respectively connected to the drain of the tenth MOS tube of the differential common-gate amplifier, the gate of the ninth MOS tube is connected to the external LO+ terminal, the source of the ninth MOS tube and the source of the eighth MOS tube are respectively connected to the drain of the eleventh MOS tube of the differential common-gate amplifier, the gate of the seventh MOS tube is connected to the gate of the eighth MOS tube, the drain of the seventh MOS tube is connected to the gate of the ninth MOS tube and then connected to the TXO+ terminal, and the drain of the eighth MOS tube is connected to the gate of the sixth MOS tube and then connected to the TXO- terminal.

[0016] Wherein, the differential common-gate amplifier comprises:

[0017] a tenth MOS tube, an eleventh MOS tube, a twelfth MOS tube and a thirteenth MOS tube;

[0018] The gates of the tenth MOS tube and the eleventh MOS tube are connected to the second power supply terminal, the twelfth MOS tube and the thirteenth MOS tube are connected to the gates and then connected to the third power supply terminal, the source of the tenth MOS tube is connected to the drain of the twelfth MOS tube, the source of the eleventh MOS tube is connected to the drain of the thirteenth MOS tube, and the sources of the twelfth MOS tube and the thirteenth MOS tube are both grounded.

[0019] Wherein, the transconductance amplifier is connected to the differential common-gate amplifier and comprises:

[0020] The drain of the fourth MOS tube of the transconductance amplifier is connected to the source of the tenth MOS tube of the differential common-gate amplifier, and the drain of the fifth MOS tube of the transconductance amplifier is connected to the source of the eleventh MOS tube of the differential common-gate amplifier.

[0021] Wherein, the differential common-gate amplifier is connected to the Gilbert mixer and comprises:

[0022] The source of the sixth MOS tube and the source of the seventh MOS tube in the Gilbert mixer are respectively connected to the drain of the tenth MOS tube of the differential common-gate amplifier, and the source of the ninth MOS tube and the source of the eighth MOS tube in the Gilbert mixer are respectively connected to the drain of the eleventh MOS tube of the differential common-gate amplifier.

[0023] Wherein, the transconductance amplifier is connected to the Gilbert mixer and comprises:

[0024] The source of the first MOS tube of the transconductance amplifier is connected to the inductor of the Gilbert mixer and then grounded.

[0025] Compared with the traditional mixer, the present invention reduces spurious signals, reduces LO feedthrough and improves linearity performance under the condition of the same power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 is a schematic diagram of a folded cascode mixer provided by an embodiment of the present invention;

[0028] Figure 2 1 is a schematic circuit diagram of a folded cascode mixer provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Figure 1 is a schematic diagram of a folded cascode mixer provided by an embodiment of the present invention, wherein the mixer comprises:

[0031] Transconductance amplifier 101, Gilbert mixer 102, differential common-gate amplifier 103;

[0032] The transconductance amplifier 101 is connected to the differential common-gate amplifier 103, the differential common-gate amplifier 103 is connected to the Gilbert mixer 102, and the transconductance amplifier 101 is connected to the Gilbert mixer 102; wherein the transconductance amplifier 101 is used for voltage-to-current conversion, the differential common-gate amplifier 103 is used for absorbing the AC output current of the transconductance amplifier 101, and the Gilbert mixer 102 is used for mixing;

[0033] The transconductance amplifier 101 receives a TXI signal, and the Gilbert mixer 102 receives a LO signal, mixes the TXI signal with the LO signal, and outputs the mixed signals.

[0034] Figure 2 is a schematic circuit diagram of a folded cascode mixer provided by an embodiment of the present invention, wherein the transconductance amplifier comprises:

[0035] A first MOS tube, a second MOS tube, a third MOS tube, a fourth MOS tube and a fifth MOS tube, a first resistor, a second resistor, a first capacitor and a second capacitor;

[0036] The source of the first MOS tube is connected to the power supply end, the gate is connected to the first power supply end, the drain is respectively connected to the sources of the second MOS tube and the third MOS tube, the drain of the second MOS tube is connected to the drain of the fourth MOS tube, the drain of the third MOS tube is connected to the drain of the fifth MOS tube, the gate of the second MOS tube is connected to the gate of the fourth MOS tube, the gate of the third MOS tube is connected to the gate of the fifth MOS tube, the first resistor is connected between the drain and the gate of the second MOS tube, the second resistor is connected between the drain and the gate of the third MOS tube, one end of the first capacitor is connected to the external TXI+ end, and the other end is connected to the gate of the second MOS tube, one end of the second capacitor is connected to the external TXI- end, and the other end is connected to the gate of the third MOS tube, and the sources of the fourth MOS tube and the fifth MOS tube are both grounded.

[0037] Wherein, the Gilbert mixer comprises:

[0038] Inductor, variable capacitor, sixth MOS tube, seventh MOS tube, eighth MOS tube, ninth MOS tube;

[0039] After the inductor is connected in parallel with the variable capacitor, one end is connected to the drain of the sixth MOS tube, and the other end is connected to the drain of the ninth MOS tube;

[0040] The gate of the sixth MOS tube is connected to the external LO+ terminal, the source of the sixth MOS tube and the source of the seventh MOS tube are respectively connected to the drain of the tenth MOS tube of the differential common-gate amplifier, the gate of the ninth MOS tube is connected to the external LO+ terminal, the source of the ninth MOS tube and the source of the eighth MOS tube are respectively connected to the drain of the eleventh MOS tube of the differential common-gate amplifier, the gate of the seventh MOS tube is connected to the gate of the eighth MOS tube, the drain of the seventh MOS tube is connected to the gate of the ninth MOS tube and then connected to the TXO+ terminal, and the drain of the eighth MOS tube is connected to the gate of the sixth MOS tube and then connected to the TXO- terminal.

[0041] Wherein, the differential common-gate amplifier comprises:

[0042] a tenth MOS tube, an eleventh MOS tube, a twelfth MOS tube and a thirteenth MOS tube;

[0043] The gates of the tenth MOS tube and the eleventh MOS tube are connected to the second power supply terminal, the twelfth MOS tube and the thirteenth MOS tube are connected to the gates and then connected to the third power supply terminal, the source of the tenth MOS tube is connected to the drain of the twelfth MOS tube, the source of the eleventh MOS tube is connected to the drain of the thirteenth MOS tube, and the sources of the twelfth MOS tube and the thirteenth MOS tube are both grounded.

[0044] Wherein, the transconductance amplifier is connected to the differential common-gate amplifier and comprises:

[0045] The drain of the fourth MOS tube of the transconductance amplifier is connected to the source of the tenth MOS tube of the differential common-gate amplifier, and the drain of the fifth MOS tube of the transconductance amplifier is connected to the source of the eleventh MOS tube of the differential common-gate amplifier.

[0046] Wherein, the differential common-gate amplifier is connected to the Gilbert mixer and comprises:

[0047] The source of the sixth MOS tube and the source of the seventh MOS tube in the Gilbert mixer are respectively connected to the drain of the tenth MOS tube of the differential common-gate amplifier, and the source of the ninth MOS tube and the source of the eighth MOS tube in the Gilbert mixer are respectively connected to the drain of the eleventh MOS tube of the differential common-gate amplifier.

[0048] Wherein, the transconductance amplifier is connected to the Gilbert mixer and comprises:

[0049] The source of the first MOS tube of the transconductance amplifier is connected to the inductor of the Gilbert mixer and then grounded.

[0050] Transistors M2, M3, M4, and M5 together with feedback resistors R1 and R2 and the tail current source transistor of M1 form a transconductance amplifier for V to I conversion. It adopts a push-pull structure with current multiplexing to improve its linearity and reduce power consumption. In addition, since the DC offset of the transconductance amplifier is blocked by the AC coupling capacitors C3 and C4, the size of M2, M3, M4, and M5 can be optimized to improve linearity regardless of their DC offset voltage. Transistors M10 and M11 and the current source transistors of M12 and M13 together form a differential common-gate amplifier to absorb the AC output current of the transconductance amplifier. It is worth noting that the DC offset of the common-gate amplifier will also cause LO feedthrough to the output of the mixer. Since M12 and M13 only handle DC current, a large and high overdrive voltage can be selected for the current source transistors of M12 and M13 to reduce the DC offset between the two branches. M10 and M11, as common-source and common-gate devices for M12 and M13, contribute little to the DC offset. In addition, the low input impedance provided by M10 and M11 helps reduce the output voltage swing of the transconductance amplifier, further improving its linearity. In addition, M10 and M11 also increase the isolation from TXI to LO and TXI to TXO ports.

[0051] By comparing with the traditional Gilbert cell mixer, the effectiveness of the folded cascode mixer proposed in this invention in reducing LO feedthrough is verified. We make the following assumptions: 1) the two mixers consume the same current IB; 2) the output swings of the two mixers have the same voltage margin; 3) only the mismatch of the transistor threshold voltage, i.e., V OS ≈ΔV th ;4)ΔVth is inversely proportional to the square root of the transistor area.

[0052] In the studied folded cascode mixer, M1 occupies half of IB, while M12 and M13 occupies one quarter of IB each. Therefore, the current flowing through the transconductance transistor is only half of that in the Gilbert cell mixer. However, since our transconductance amplifier reuses the current in the PMOS and NMOS transistors, its total transconductance is the same as that in the Gilbert cell mixer assuming the same overdrive voltage for all transistors. For both mixers, the AC signal current flowing to the LO switch quadrupole should be almost the same for the same amplitude TXI input. The input capacitance added by using a push-pull transconductor can be absorbed into the input matching network, so this mixer is used for narrow-band applications.

[0053] Now, let’s compare the DC offset current flowing into the LO switch quadrupole. The DC offset current of the folded cascode mixer can be expressed as: gm M11 ×Vos_ M11 , where gm M12is the transconductance of transistor M12, V OS_M12 is the offset voltage between transistors M12 and M13. The expression for the dc offset current of the Gilbert cell mixer is similar to: gm M2 ×Vos_ M2 , where gm M3 is the transconductance of transistor M2, V OS_M2 is the offset voltage between M2 and M3. The current in M12 of the folded cascode mixer is half the current in M2 in the Gilbert cell mixer. By choosing the same width for M12 and M2, while making M12 twice as long as M2, we can keep the overdrive voltage of M12 and M2 the same. Therefore, the output voltage fluctuations of these two mixers will have similar headroom. Their offset voltage and transconductance can be expressed as:

[0054]

[0055]

[0056] Therefore, we calculate the DC offset current ratio between the two mixers as:

[0057]

[0058] Since their AC signal currents are the same, the folded cascode mixer we designed can reduce LO feedthrough compared to the Gilbert cell mixer.

[0059] As an embodiment of the present invention, the folded common-source common-gate mixer can be designed using a 0.11μm CMOS process. Its die size is 0.146 square millimeters. The mixer draws a total current of 2.6mA from a 1.2V power supply, of which the transconductance amplifier is 1.2mA, and the common-gate amplifier and the four LO switches are 1.4mA. In the simulation, the differential amplitude of the TXI input is set to 400mVP-P, and its frequency is 2453MHz. The 3345MHz LO is AC-coupled with the four LO switches at a DC bias of 1.1V. The differential amplitude of the LO is 800mVP-P to keep the switch quadrupole in the saturation region. The mixer has an ideal voltage buffer for driving a 50Ω port. The output power of the mixer is 4.77dBm at 5.798GHz, and the maximum mixing spurious is the sideband image of 892MHz, i.e. -36.14dBm. The second spurious frequency is 782MHz with -42.55dBm, which is from the fundamental input of TXI mixed with the third harmonic LO in the lower sideband. The third largest spurious frequency is 4014MHz with -42.63dBm, which is caused by the third harmonic of the input TXI mixed with the LO fundamental in the lower sideband. All spurious signals are -40dBc lower than the desired signal.

[0060] The folded cascode mixer for 2.4GHz to 5.8GHz transmitters has a 9.2db reduction in spurious performance compared to conventional Gilbert cell mixers with the same power consumption. The mixer is designed in 0.11μm CMOS and consumes 2.6mA at a 1.2V supply voltage. Its output 1dB compression point is 3.84dBm, and all transmit spurious performance is well below -40dBc.

[0061] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A folded cascode mixer, characterized in that: include: Transconductance amplifier, differential common-gate amplifier, Gilbert mixer; The transconductance amplifier is connected to the differential common-gate amplifier, the differential common-gate amplifier is connected to the Gilbert mixer, and the transconductance amplifier is connected to the Gilbert mixer; wherein the transconductance amplifier is used for voltage-to-current conversion, the differential common-gate amplifier is used for absorbing the AC output current of the transconductance amplifier, and the Gilbert mixer is used for mixing; The Gilbert mixer includes an inductor, a variable capacitor, a sixth MOS tube, a seventh MOS tube, an eighth MOS tube and a ninth MOS tube; the source of the sixth MOS tube and the source of the seventh MOS tube are respectively connected to the drain of the tenth MOS tube of the differential common-gate amplifier, and the source of the ninth MOS tube and the source of the eighth MOS tube are respectively connected to the drain of the eleventh MOS tube of the differential common-gate amplifier; The transconductance amplifier is connected to the differential common-gate amplifier and comprises: The drain of the fourth MOS tube of the transconductance amplifier is connected to the source of the tenth MOS tube of the differential common-gate amplifier, and the drain of the fifth MOS tube of the transconductance amplifier is connected to the source of the eleventh MOS tube of the differential common-gate amplifier; The transconductance amplifier is connected to the Gilbert mixer and comprises: The source of the first MOS tube of the transconductance amplifier is connected to the inductor of the Gilbert mixer and then connected to the VDD power supply terminal; The transconductance amplifier receives a TXI signal, and the Gilbert mixer receives an LO signal and mixes the TXI signal with the LO signal and outputs the mixed signals.

2. The folded cascode mixer according to claim 1, characterized in that: The transconductance amplifier comprises: a first MOS tube, a second MOS tube, a third MOS tube, a fourth MOS tube and a fifth MOS tube, a first resistor, a second resistor, a first capacitor and a second capacitor; The source of the first MOS tube is connected to the VDD power supply terminal, the gate is connected to the first power supply terminal, the drain is respectively connected to the sources of the second MOS tube and the third MOS tube, the drain of the second MOS tube is connected to the drain of the fourth MOS tube, the drain of the third MOS tube is connected to the drain of the fifth MOS tube, the gate of the second MOS tube is connected to the gate of the fourth MOS tube, the gate of the third MOS tube is connected to the gate of the fifth MOS tube, the first resistor is connected between the drain and the gate of the second MOS tube, the second resistor is connected between the drain and the gate of the third MOS tube, one end of the first capacitor is connected to the external TXI+ terminal, and the other end is connected to the gate of the second MOS tube, one end of the second capacitor is connected to the external TXI- terminal, and the other end is connected to the gate of the third MOS tube, and the sources of the fourth MOS tube and the fifth MOS tube are both grounded.

3. The folded cascode mixer according to claim 1, characterized in that: After the inductor is connected in parallel with the variable capacitor, one end is connected to the drain of the sixth MOS tube, and the other end is connected to the drain of the ninth MOS tube; The gate of the sixth MOS tube is connected to the external LO+ terminal, the gate of the ninth MOS tube is connected to the external LO+ terminal, the gate of the seventh MOS tube is connected to the gate of the eighth MOS tube, the drain of the seventh MOS tube is connected to the gate of the ninth MOS tube and then connected to the TXO+ terminal, and the drain of the eighth MOS tube is connected to the gate of the sixth MOS tube and then connected to the TXO- terminal.

4. The folded cascode mixer according to claim 1, characterized in that: The differential common-gate amplifier comprises: a tenth MOS tube, an eleventh MOS tube, a twelfth MOS tube and a thirteenth MOS tube; The gates of the tenth MOS tube and the eleventh MOS tube are connected to the second power supply terminal, the twelfth MOS tube and the thirteenth MOS tube are connected to the gates and then connected to the third power supply terminal, the source of the tenth MOS tube is connected to the drain of the twelfth MOS tube, the source of the eleventh MOS tube is connected to the drain of the thirteenth MOS tube, and the sources of the twelfth MOS tube and the thirteenth MOS tube are both grounded.

5. The folded cascode mixer according to claim 1, characterized in that: The differential common-gate amplifier is connected to the Gilbert mixer and comprises: The source of the sixth MOS tube and the source of the seventh MOS tube in the Gilbert mixer are respectively connected to the drain of the tenth MOS tube of the differential common-gate amplifier, and the source of the ninth MOS tube and the source of the eighth MOS tube in the Gilbert mixer are respectively connected to the drain of the eleventh MOS tube of the differential common-gate amplifier.

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