Double-second-order low-pass filter and high-frequency active non-inductive low-pass filter circuit

Abstract

The invention relates to a double-second-order low-pass filter and a high-frequency active non-inductive low-pass filter circuit, belongs to the technical field of filter circuits, and solves the problem that a broadband low-pass filter about 10 GHz is difficult to realize in the existing CMOS (complementary metal oxide semiconductor) technology. The double-second-order low-pass filter comprises a main transconductance amplifier circuit, a second transconductance amplifier circuit, a third transconductance amplifier circuit, a fourth transconductance amplifier circuit and a fourth transconductance amplifier circuit, the anode output end and the cathode output end of the main transconductance amplifier circuit are respectively connected with the anode input end and the cathode input end of the equivalent RLC load circuit; the anode output end and the cathode output end of the equivalent RLC load circuit are respectively connected with the input end of the anode output circuit and the input end of the cathode output circuit; the output ends of the positive electrode output circuit and the negative electrode output circuit are used for outputting differential signals; and the bias current source circuit is used for respectively providing a bias current source for the main transconductance amplifier circuit, the equivalent RLC load circuit, the positive output circuit and the negative output circuit. And a low-pass filter of about 10 GHz is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of filter circuits, and in particular, to a biquadratic low-pass filter and a high-frequency active inductorless low-pass filter circuit. Background Art

[0002] With the development of science and technology, high-frequency (about 10 GHz) low-pass filters with a cut-off frequency as high as several GHz are very necessary in some application fields, such as in high-frequency and high-speed circuit fields such as broadband spectrum monitoring, high-bit-rate optical communication, broadband measurement systems, high-speed data converters operating at a sampling rate higher than 10 GS / s, and asynchronous time-interleaved (ATI) digital converters.

[0003] However, at relatively low frequencies around 10 GHz, the size of the passive inductor element in the filter circuit is a problem. The larger inductor element occupies a very large chip area, resulting in the low-pass filter circuit used in the prior art around 10 GHz not being able to meet the increasingly miniaturized requirements of integrated circuits.

[0004] Therefore, there is an urgent need for a new technical solution for low-pass filter circuits. Summary of the Invention

[0005] In view of the above analysis, embodiments of the present invention aim to provide a biquadratic low-pass filter and a high-frequency active inductorless low-pass filter circuit to solve the problem that it is difficult to implement a broadband low-pass filter around 10 GHz in the existing CMOS technology.

[0006] On the one hand, embodiments of the present invention provide

[0007] A biquadratic low-pass filter, the biquadratic low-pass filter includes a main transconductance amplifier circuit, an equivalent RLC load circuit, a positive output circuit, a negative output circuit, and a bias current source circuit;

[0008] The positive and negative input terminals of the main transconductance amplifier circuit are used to receive the input differential signal; the positive output terminal and the negative output terminal of the main transconductance amplifier circuit are respectively connected to the positive input terminal and the negative input terminal of the equivalent RLC load circuit;

[0009] The positive output terminal and the negative output terminal of the equivalent RLC load circuit are respectively connected to the input terminal of the positive output circuit and the input terminal of the negative output circuit; the output terminals of the positive output circuit and the negative output circuit are used to output differential signals;

[0010] The bias current source circuit is used to provide bias current sources for the main transconductance amplifier circuit, the equivalent RLC load circuit, the positive output circuit, and the negative output circuit respectively.

[0011] Based on the further improvement of the above-mentioned biquadratic low-pass filter, the main transconductance amplifier circuit includes a current negative feedback left resistor REL, a current negative feedback right resistor RER, a first left transistor Q1L, and a first right transistor Q1R;

[0012] The bases of the first left transistor Q1L and the first right transistor Q1R are respectively the positive input terminal and the negative input terminal of the main transconductance amplifier circuit; the collectors of the first left transistor Q1L and the first right transistor Q1R are respectively the positive output terminal and the negative output terminal of the main transconductance amplifier circuit;

[0013] The emitter of the first left transistor Q1L is connected to one end of the current negative feedback left resistor REL, and the emitter of the first right transistor Q1R is connected to one end of the current negative feedback right resistor RER;

[0014] The other ends of the current negative feedback left resistor REL and the current negative feedback right resistor RER are connected together for connecting to a bias current source.

[0015] Based on the further improvement of the above-mentioned biquadratic low-pass filter, the equivalent RLC load circuit includes a first capacitor C1, a second capacitor C2, a collector left resistor RCL, a collector right resistor RCR, and a cross-coupling structure;

[0016] The cross-coupling structure is used to convert the second capacitor C2 from a capacitor to an inductor using a positive feedback impedance converter, and includes two input terminals and two output terminals; a first capacitor C1 is connected between the two input terminals, and at the same time, they are respectively used as the positive input terminal and the negative input terminal of the equivalent RLC load circuit;

[0017] A second capacitor C2 is connected between the two output terminals, and at the same time, they are respectively used as the positive output terminal and the negative output terminal of the equivalent RLC load circuit;

[0018] The two output terminals are also respectively grounded through the collector left resistor RCL and the collector right resistor RCR.

[0019] Based on the further improvement of the above-mentioned biquadratic low-pass filter, the cross-coupling structure includes a second left transistor Q2L and a second right transistor Q2R;

[0020] The emitters of the second left transistor Q2L and the second right transistor Q2R are respectively the two input terminals of the cross-coupling structure;

[0021] The collectors of the second left transistor Q2L and the second right transistor Q2R are respectively the two output terminals of the cross-coupling structure;

[0022] The base and the collector of the second left transistor Q2L are cross-connected to the collector and the base of the second right transistor Q2R.

[0023] Based on the further improvement of the above-mentioned biquadratic low-pass filter, the left collector resistor RCL and the right collector resistor RCR are the same;

[0024] The second left transistor Q2L and the second right transistor Q2R are the same;

[0025] The first left transistor Q1L and the first right transistor Q1R are the same;

[0026] The left current negative feedback resistor REL and the right current negative feedback resistor RER are the same.

[0027] Based on the further improvement of the above-mentioned biquadratic low-pass filter, the positive output circuit includes a fourth left transistor Q4L, a fifth left transistor Q5L, and a sixth left transistor Q6L;

[0028] The collector of the fourth left transistor Q4L is grounded, and the base of the fourth left transistor Q4L is the input terminal of the positive output circuit; the emitter of the fourth left transistor Q4L is connected to both the collector and the base of the fifth left transistor Q5L at the same time;

[0029] The emitter of the fifth left transistor Q5L is

[0030] connected to both the collector and the base of the sixth left transistor Q6L at the same time, and is the output terminal of the positive output circuit at the same time;

[0031] The emitter of the sixth left transistor Q6L is used to connect to a bias current source.

[0032] Based on the further improvement of the above-mentioned biquadratic low-pass filter, the negative output circuit includes a fourth right transistor Q4R, a fifth right transistor Q5R, and a sixth right transistor Q6R;

[0033] The collector of the fourth right transistor Q4R is grounded, and the base of the fourth right transistor Q4R is the input terminal of the negative output circuit; the emitter of the fourth right transistor Q4R is connected to both the collector and the base of the fifth right transistor Q5R at the same time;

[0034] The emitter of the fifth right transistor Q5R is connected to both the collector and the base of the sixth right transistor Q6R at the same time, and is the output terminal of the negative output circuit at the same time;

[0035] The emitter of the sixth right transistor Q6R is used to connect to a bias current source.

[0036] Based on the further improvement of the above-mentioned biquadratic low-pass filter, the bias current source circuit includes a seventh left transistor Q7L, a seventh right transistor Q7R, a third transistor Q3, a first bias left resistor R1L, a first bias right resistor R1R, and a second resistor R2;

[0037] The collectors of the seventh left transistor Q7L, the seventh right transistor Q7R, and the third transistor Q3 respectively output bias current sources for the positive output circuit, the main transconductance amplifier circuit, and the negative output circuit;

[0038] The bases of the seventh left transistor Q7L, the seventh right transistor Q7R, and the third transistor Q3 are respectively connected to a bias voltage;

[0039] The emitters of the seventh left transistor Q7L, the seventh right transistor Q7R, and the third transistor Q3 are respectively connected to the power supply voltage through the first bias left resistor R1L, the first bias right resistor R1R, and the second resistor R2.

[0040] Based on the further improvement of the above-mentioned biquadratic low-pass filter, the first left transistor Q1L, the first right transistor Q1R, the second left transistor Q2L, the second right transistor Q2R, the third transistor Q3, the fourth left transistor Q4L, the fourth right transistor Q4R, the fifth left transistor Q5L, the fifth right transistor Q5R, the sixth left transistor Q6L, the sixth right transistor Q6R, the seventh left transistor Q7L, and the seventh right transistor Q7R all adopt DHBT transistors with an indium phosphide substrate.

[0041] On the other hand, an embodiment of the present invention provides a high-frequency active non-inductive low-pass filter circuit. The high-frequency active non-inductive low-pass filter circuit includes an input buffer unit, a first-stage biquadratic low-pass filter, a second-stage biquadratic low-pass filter, a third-stage biquadratic low-pass filter, a fourth-stage biquadratic low-pass filter, and an output buffer unit connected in series in sequence;

[0042] The input buffer unit is used to receive the differential signal to be filtered;

[0043] The first-stage biquadratic low-pass filter, the second-stage biquadratic low-pass filter, the third-stage biquadratic low-pass filter, and the fourth-stage biquadratic low-pass filter are based on the biquadratic low-pass filter described in the above-mentioned one aspect, and are used to filter the differential signal to be filtered in sequence;

[0044] The output buffer unit is used to output the filtered differential signal.

[0045] Compared with the prior art, the present invention can at least achieve one of the following beneficial effects:

[0046] 1. A biquadratic low-pass filter is formed by the main transconductance amplifier circuit and the equivalent RLC load circuit, and the input differential signal is filtered in the form of an equivalent inductor, avoiding the use of an inductor from occupying a large area and reducing the occupied area of the filter;

[0047]

[0048] ​2. The loss of the filtered signal reflected back is small through the positive output circuit and the negative output circuit, with good impedance matching, small insertion loss, good transmission characteristics, and high out-of-band rejection characteristics;

[0049] 3. An equivalent inductor is constructed through the cross-coupling structure, the second capacitor C2, the left collector resistor RCL, and the right collector resistor RCR, enabling the biquadratic low-pass filter to have good linearity and can be used as an anti-aliasing filter at the front end of a high-speed data converter;

[0050] 4. The biquadratic low-pass filter adopts a left-right symmetric fully differential structure to simultaneously process the input signal in the same way, resulting in a small distortion degree of the output signal of the filter circuit and good fidelity;

[0051] 5. The four-stage high-frequency active inductorless low-pass filter circuit based on the biquadratic low-pass filter has a large stopband attenuation and good filtering effect, and can achieve high-frequency filtering of signals with a frequency greater than 8 GHz.

[0052] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be made obvious from the specification or understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the content specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The drawings are only for the purpose of showing specific embodiments and are not considered as limiting the present invention. Throughout the drawings, the same reference signs represent the same components.

[0054] Figure 1 It is a schematic structural diagram of the biquadratic low-pass filter provided by an embodiment of the present invention;

[0055] Figure 2 It is a schematic structural diagram of the high-frequency active inductorless low-pass filter circuit provided by an embodiment of the present invention;

[0056] Figure 3 It is a parameter simulation curve graph of the differential input port return loss SDD11 and the differential output port reflection coefficient SDD22 provided by an embodiment of the present invention;

[0057] Figure 4 It is a parameter simulation curve graph of the differential input signal stopband suppression SDD21 provided by an embodiment of the present invention;

[0058] Figure 5 It is a parameter simulation curve graph of the 1 dB compression point when the input signal frequency Fin = 1 GHz provided by an embodiment of the present invention;

[0059] Figure 6 The simulation curve graph of the total harmonic distortion (THD) parameter when the input signal power Pin = -6dBm provided by the embodiment of the present invention;

[0060] Figure 7 (a) The simulation curve graph of the transient response of the output signal when the input signal frequency Fin = 7GHz provided by the embodiment of the present invention;

[0061] Figure 7 (b) The simulation curve graph of the transient response of the output signal when the input signal frequency Fin = 13GHz provided by the embodiment of the present invention. Detailed implementation manners

[0062] The preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. The accompanying drawings form a part of this application and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

[0063] A specific embodiment of the present invention discloses a biquadratic low-pass filter, as Figure 1 shown. The biquadratic low-pass filter includes a main transconductance amplifier circuit, an equivalent RLC load circuit, a positive output circuit, a negative output circuit, and a bias current source circuit;

[0064] The positive and negative input terminals of the main transconductance amplifier circuit are used to receive the input differential signal; the positive output terminal and the negative output terminal of the main transconductance amplifier circuit are respectively connected to the positive input terminal and the negative input terminal of the equivalent RLC load circuit;

[0065] The positive output terminal and the negative output terminal of the equivalent RLC load circuit are respectively connected to the input terminal of the positive output circuit and the input terminal of the negative output circuit; the output terminals of the positive output circuit and the negative output circuit are used to output the differential signal;

[0066] The bias current source circuit is used to provide bias current sources for the main transconductance amplifier circuit, the equivalent RLC load circuit, the positive output circuit, and the negative output circuit respectively.

[0067] Specifically, as Figure 1 shown, the VIP port and the VIN port are respectively the positive input terminal and the negative input terminal of the biquadratic low-pass filter, and are used to receive the positive and negative of the input differential signal; the VOP port and the VON port are respectively the positive output terminal and the negative output terminal of the biquadratic low-pass filter. The input differential signal is input into the biquadratic low-pass filter through the VIP port and the VIN port, and finally output from the VOP port and the VON port of the biquadratic low-pass filter to obtain the filtered differential signal, with small insertion loss, good transmission characteristics, and good fidelity in the filtering circuit.

[0068] Specifically, asFigure 1 As shown, the input differential signal is filtered successively through the main transconductance amplifier circuit and the equivalent RLC load circuit, and finally

[0069] it is output through the positive output circuit and the negative output circuit. The bias current source circuit is used to provide bias current sources for the main transconductance amplifier circuit, the equivalent RLC load circuit, the positive output circuit, and the negative output circuit respectively.

[0070] Preferably, as Figure 1 shown, the main transconductance amplifier circuit includes a current negative feedback left resistor REL, a current negative feedback right resistor RER, a first left transistor Q1L, and a first right transistor Q1R;

[0071] The bases of the first left transistor Q1L and the first right transistor Q1R are the positive input terminal and the negative input terminal of the main transconductance amplifier circuit respectively; the collectors of the first left transistor Q1L and the first right transistor Q1R are the positive output terminal and the negative output terminal of the main transconductance amplifier circuit respectively;

[0072] The emitter of the first left transistor Q1L is connected to one end of the current negative feedback left resistor REL, and the emitter of the first right transistor Q1R is connected to one end of the current negative feedback right resistor RER;

[0073] The other ends of the current negative feedback left resistor REL and the current negative feedback right resistor RER are connected together for connecting to a bias current source.

[0074] Specifically, as Figure 1 shown, the collectors of the first left transistor Q1L and the first right transistor Q1R are the positive output terminal and the negative output terminal of the main transconductance amplifier circuit respectively, the bases of the first left transistor Q1L and the first right transistor Q1R are the positive input terminal and the negative input terminal of the main transconductance amplifier circuit respectively, and the other ends of the current negative feedback left resistor REL and the current negative feedback right resistor RER are used for connecting to a bias current source.

[0075] Specifically, under the control of the first left transistor Q1L and the first right transistor Q1R, on the one hand, the input differential signal accesses the bias current source circuit through the current negative feedback left resistor REL and the current negative feedback right resistor RER, and on the other hand, it flows to the equivalent RLC load circuit through the collectors of the first left transistor Q1L and the first right transistor Q1R, converting the voltage of the differential signal into current to achieve a biquadratic low-pass filter transfer function.

[0076] Preferably, as Figure 1 shown, the equivalent RLC load circuit includes a first capacitor C1, a second capacitor C2, a collector left resistor

[0077] RCL, collector left resistor RCL, collector right resistor RCR, and cross-coupling structure;

[0078] The cross-coupling structure is used to convert the second capacitor C2 from a capacitor to an inductor using a positive feedback impedance converter, and includes two input terminals and two output terminals; a first capacitor C1 is connected between the two input terminals, and at the same time, they serve as the positive input terminal and the negative input terminal of the equivalent RLC load circuit respectively;

[0079] A second capacitor C2 is connected between the two output terminals, and at the same time, they serve as the positive output terminal and the negative output terminal of the equivalent RLC load circuit respectively;

[0080] The two output terminals are also grounded through the collector left resistor RCL and the collector right resistor RCR respectively.

[0081] Specifically, as Figure 1 shown, the cross-coupling structure includes two input terminals, namely the positive input terminal and the negative input terminal; the cross-coupling structure includes two output terminals, namely the positive output terminal and the negative output terminal.

[0082] In the equivalent RLC load circuit, the positive input terminal of the cross-coupling structure is connected to one end of the first capacitor C1, and the negative input terminal of the cross-coupling structure is connected to the other end of the first capacitor C1. When the biquadratic low-pass filter is working, the first capacitor C1 is used to store charge. At the same time, the positive output terminal of the cross-coupling structure is connected to one end of the second capacitor C2, and the negative output terminal of the cross-coupling structure is connected to the other end of the second capacitor C2. When the biquadratic low-pass filter is working, the second capacitor C2 is used to store charge.

[0083] Specifically, as Figure 1 shown, the positive output terminal of the cross-coupling structure is connected to one end of the collector left resistor RCL, and the other end of the collector left resistor RCL is grounded; the negative output terminal of the cross-coupling structure is connected to one end of the collector right resistor RCR, and the other end of the collector right resistor RCR is grounded.

[0084] Specifically, as Figure 1 shown, the positive input terminal and the negative input terminal of the cross-coupling structure serve as the positive input terminal and the negative input terminal of the equivalent RLC load circuit. The positive output terminal of the cross-coupling structure, one end of the second capacitor C2, and one end of the collector left resistor RCL serve as the positive output terminal of the equivalent RLC load circuit at the same time;

[0085] The negative output terminal of the cross-coupling structure, the other end of the second capacitor C2, and one end of the collector right resistor RCR serve as the negative output terminal of the equivalent RLC load circuit at the same time.

[0086] It should be noted that in the equivalent RLC load circuit, the cross-coupling structure and the second capacitor C2 form an equivalent active inductor, which, combined with the first capacitor C1, the left collector resistor RCL, and the right collector resistor RCR, constitutes an equivalent RLC load for both biasing purposes and setting the value of the quality factor of the biquadratic low-pass filter.

[0087] Preferably, as Figure 1 shown, the cross-coupling structure includes a second left transistor Q2L and a second right transistor Q2R;

[0088] The emitters of the second left transistor Q2L and the second right transistor Q2R are respectively the two input terminals of the cross-coupling structure;

[0089] The collectors of the second left transistor Q2L and the second right transistor Q2R are respectively the two output terminals of the cross-coupling structure;

[0090] The base and collector of the second left transistor Q2L are cross-connected to the collector and base of the second right transistor Q2R.

[0091] Specifically, as Figure 1 shown, the emitter of the second left transistor Q2L is the positive input terminal of the cross-coupling structure, and the emitter of the second right transistor Q2R is the negative input terminal of the cross-coupling structure; the collector of the second left transistor Q2L is connected to the base of the second right transistor Q2R, serving as the positive output terminal of the cross-coupling structure; the collector of the second right transistor Q2R is connected to the base of the second left transistor Q2L, serving as the negative output terminal of the cross-coupling structure, and the positive feedback impedance converter of the cross-coupling structure is used to convert the capacitance into an inductance.

[0092] Preferably, as Figure 1 shown, the left collector resistor RCL and the right collector resistor RCR are the same;

[0093] The second left transistor Q2L and the second right transistor Q2R are the same;

[0094] The first left transistor Q1L and the first right transistor Q1R are the same;

[0095] The left current negative feedback resistor REL and the right current negative feedback resistor RER are the same.

[0096] Specifically, as Figure 1As shown, the left collector resistor RCL, the second left transistor Q2L, the first left transistor Q1L, and the first left transistor Q1L can be regarded as processing the positive differential signal. The right collector resistor RCR, the second right transistor Q2R, the first right transistor Q1R, and the current negative feedback right resistor RER can be regarded as processing the negative differential signal. The two are symmetrical to each other and adopt the same processing. That is, the left collector resistor RCL and the right collector resistor RCR are the same; the second left transistor Q2L and the second right transistor Q2R are the same; the first left transistor Q1L and the first right transistor Q1R are the same; the current negative feedback left resistor REL and the current negative feedback right resistor RER are the same

[0097] Preferably, as Figure 1 shown, the positive output circuit includes a fourth left transistor Q4L, a fifth left transistor Q5L, and a sixth left transistor Q6L;

[0098] The collector of the fourth left transistor Q4L is grounded, and the base of the fourth left transistor Q4L is the input terminal of the positive output circuit; the emitter of the fourth left transistor Q4L is connected to both the collector and the base of the fifth left transistor Q5L;

[0099] The emitter of the fifth left transistor Q5L is connected to both the collector and the base of the sixth left transistor Q6L and is also the output terminal of the positive output circuit;

[0100] The emitter of the sixth left transistor Q6L is used to connect to a bias current source.

[0101] Specifically, as Figure 1 shown, the VOP port can be used as the output terminal of the positive output circuit; in the positive output circuit, the positive signal of the differential signal is received through the base of the fourth left transistor Q4L and output through the emitter of the fifth left transistor Q5L, and the positive signal of the differential signal is output through the VOP port.

[0102] Specifically, as Figure 1 shown, the emitter of the sixth left transistor Q6L is used to connect to a bias current source; the collector and the base of the sixth left transistor Q6L are connected to the emitter of the fifth left transistor Q5L and serve as the output terminal VOP of the positive output circuit.

[0103] Specifically, as Figure 1 shown, the collector and the base of the fifth left transistor Q5L are connected to the emitter of the fourth left transistor Q4L.

[0104] Preferably, as Figure 1 shown, the negative output circuit includes a fourth right transistor Q4R, a fifth right transistor Q5R, and a sixth right transistor Q6R;

[0105] The collector of the fourth right transistor Q4R is grounded, and the base of the fourth right transistor Q4R is the input terminal of the negative output circuit; the emitter of the fourth right transistor Q4R is connected to both the collector and the base of the fifth right transistor Q5R.

[0106] The emitter of the fifth right transistor Q5R is connected to both the collector and the base of the sixth right transistor Q6R, and is also the output terminal of the negative output circuit.

[0107] The emitter of the sixth right transistor Q6R is used to connect to a bias current source.

[0108] Specifically, as Figure 1 shown, the VON port can be used as the output terminal of the negative output circuit; in the negative output circuit, the negative signal of the differential signal is received through the base of the fourth right transistor Q4R and output through the emitter of the fifth right transistor Q5R, and the negative signal of the differential signal is output through the VON port.

[0109] Specifically, as Figure 1 shown, the emitter of the sixth right transistor Q6R is used to connect to a bias current source; the collector and the base of the sixth right transistor Q6R are connected to the emitter of the fifth right transistor Q5R, serving as the output terminal VON of the negative output circuit.

[0110] Specifically, as Figure 1 shown, the collector and the base of the fifth right transistor Q5R are connected to the emitter of the fourth right transistor Q4R.

[0111] Preferably, as Figure 1 shown, the bias current source circuit includes a seventh left transistor Q7L, a seventh right transistor Q7R, a third transistor Q3, a first bias left resistor R1L, a first bias right resistor R1R, and a second resistor R2;

[0112] The collectors of the seventh left transistor Q7L, the seventh right transistor Q7R, and the third transistor Q3 respectively output bias current sources for the positive output circuit, the main transconductance amplifier circuit, and the negative output circuit;

[0113] The bases of the seventh left transistor Q7L, the seventh right transistor Q7R, and the third transistor Q3 are respectively connected to bias voltages;

[0114] The emitters of the seventh left transistor Q7L, the seventh right transistor Q7R, and the third transistor Q3 are respectively connected to the power supply voltage through the first bias left resistor R1L, the first bias right resistor R1R, and the second resistor R2.

[0115] Specifically, as Figure 1As shown, in the bias current source circuit, there are a positive output circuit, a main transconductance amplifier circuit, a negative output circuit, and an output bias current source respectively, enabling the biquadratic low-pass filter to operate. The structures of the positive output circuit and the negative output circuit are emitter followers, which adjust the input and output common-mode levels and increase the bandwidth. The bias current source circuit provides DC bias for the positive output circuit, the main transconductance amplifier circuit, and the negative output circuit.

[0116] Specifically, as Figure 1 shown, the emitters of the seventh left transistor Q7L, the seventh right transistor Q7R, and the third transistor Q3 are connected to the power supply voltage through the first bias left resistor R1L, the first bias right resistor R1R, and the second resistor R2 respectively; the bases of the seventh left transistor Q7L, the seventh right transistor Q7R, and the third transistor Q3 are connected to the bias voltage Vbias respectively.

[0117] Preferably, as Figure 1 shown, the fourth left transistor Q4L and the fourth right transistor Q4R are the same;

[0118] the fifth left transistor Q5L and the fifth right transistor Q5R are the same;

[0119] the sixth left transistor Q6L and the sixth right transistor Q6R are the same;

[0120] the seventh left transistor Q7L and the seventh right transistor Q7R are the same.

[0121] Specifically, the fourth left transistor Q4L, the fourth left transistor Q4L, the sixth left transistor Q6L, and the seventh left transistor Q7L can be regarded as the circuit structure for outputting the positive differential signal, and the fourth right transistor Q4R, the fifth right transistor Q5R, the sixth right transistor Q6R, and the seventh right transistor Q7R can be regarded as the circuit structure for outputting the negative differential signal. The two are symmetric and are processed in the same way. That is, the fourth left transistor Q4L and the fourth right transistor Q4R are the same; the fifth left transistor Q5L and the fifth right transistor Q5R are the same; the sixth left transistor Q6L and the sixth right transistor Q6R are the same;

[0122] the seventh left transistor Q7L and the seventh right transistor Q7R are the same.

[0123] Preferably, the first left transistor Q1L, the first right transistor Q1R, the second left transistor Q2L, the second right transistor Q2R, the third transistor Q3, the fourth left transistor Q4L, the fourth right transistor Q4R, the fifth left transistor Q5L, the fifth right transistor Q5R, the sixth left transistor Q6L, the sixth right transistor Q6R, the seventh left transistor Q7L, and the seventh right transistor Q7R all adopt DHBT transistors with indium phosphide substrates.

[0124] Specifically, a DHBT (Double Heterojunction Bipolar Transistor) transistor based on an indium phosphide (InP) substrate has the advantages of high mobility and high cut-off frequency, and can better achieve low-pass filtering around 10 GHz. At the same time, by utilizing the good matching characteristics of the transconductance-base emitter of indium phosphide devices, it is more conducive to achieving low-noise and good linearity signal output compared to other circuits.

[0125] Another specific embodiment of the present invention discloses a high-frequency active inductorless low-pass filter circuit, as Figure 2 shown, the high-frequency active inductorless low-pass filter circuit includes an input buffer unit, a first-order biquadratic low-pass filter, a second-order biquadratic low-pass filter, a third-order biquadratic low-pass filter, a fourth-order biquadratic low-pass filter, and an output buffer unit connected in series in sequence;

[0126] The input buffer unit is used to receive the differential signal to be filtered;

[0127] The first-order biquadratic low-pass filter, the second-order biquadratic low-pass filter, the third-order biquadratic low-pass filter, and the fourth-order biquadratic low-pass filter are the biquadratic low-pass filters described in any one of the above, and are used to filter the differential signal to be filtered in sequence;

[0128] The output buffer unit is used to output the filtered differential signal.

[0129] Specifically, as Figure 2 shown, when filtering the differential signal, the attenuation amplitude of filtering can be improved by multiple biquadratic low-pass filters.

[0130] The input buffer unit and the output buffer unit are used to improve the linearity of the differential signal that can be input, increase the input range of the differential signal, and achieve 50Ω characteristic impedance matching.

[0131] The following lists several specific simulation embodiments of the high-frequency active inductorless low-pass filter circuit:

[0132] 1. As Figure 3 shown, it is the simulation curve graph of the differential input port return loss SDD11 and the differential output port reflection coefficient SDD22 parameters provided by the embodiment of the present invention. It can be seen from Figure 3 that the differential input port return loss SDD11 of the high-frequency active inductorless low-pass filter circuit provided by the embodiment of the present invention is less than -20 dB in the 30 GHz frequency band, and the differential output port reflection coefficient SDD22 is less than -15 dB in the 15 GHz frequency band. That is, in the embodiment of the present invention, the loss reflected back after passing through the fourth-order biquadratic low-pass filter is small, and the 50Ω characteristic impedance matching is good.

[0133] 2. As shown in Figure 4 , the simulation curve of the SDD21 parameter for the differential input signal stopband rejection provided by the embodiment of the present invention. It can be seen from Figure 4 that the -3dB cut-off frequency of the biquadratic low-pass filter is 7.7GHz, and the stopband rejection SDD21 is greater than -4.87dB within the 7.7GHz frequency band, indicating that the biquadratic low-pass filter has low insertion loss and good transmission characteristics. At 2 times the cut-off frequency of 15.4GHz, SDD21 < -50dB, indicating that the biquadratic low-pass filter has a good rectangularity coefficient and a steep cut-off frequency. In the stopband range of 15 - 30GHz, SDD21 < -30dB, indicating that the biquadratic low-pass filter has high out-of-band rejection characteristics.

[0134] 3. As shown in Figure 5 , the simulation curve of the 1dB compression point parameter when the input signal frequency Fin = 1GHz provided by the embodiment of the present invention. It can be seen from Figure 5 that the line1 curve is the curve of the ideal output signal power varying linearly with the input signal power. It can be seen that when the input signal frequency Fin = 1GHz, the 1dB compression point signal power is -2.5dBm, indicating that the biquadratic low-pass filter provided by the embodiment of the present invention has good linearity and can be used as an anti-aliasing filter at the front end of a high-speed data converter.

[0135] 4. As shown in Figure 6 , the simulation curve of the total harmonic distortion (THD) parameter when the input signal power Pin = -6dBm provided by the embodiment of the present invention. It can be seen from Figure 6 that when the input signal power Pin = -6dBm, within the 10GHz frequency band, the total harmonic distortion THD < -30dB, indicating that the distortion degree of the output signal of this filter circuit is small and the fidelity is good.

[0136] 5. As shown in Figure 7 , Figure 7 (a) is the simulation curve of the output signal transient response when the input signal frequency Fin = 7GHz provided by the embodiment of the present invention, Figure 7 (b) is the simulation curve of the output signal transient response when the input signal frequency Fin = 13GHz. It can be seen from Figure 7 that at the 7GHz passband, the amplitude of the output signal decreases, and the attenuation is 75% of the amplitude of the input signal. At the 13GHz stopband, the amplitude of the output signal attenuates to 3% of the amplitude of the input signal. It can be seen that the stopband attenuation is large and the filtering effect is good, and high-frequency filtering for signal frequencies greater than 8GHz can be achieved.

[0137] Compared with the prior art, the biquadratic low-pass filter and the high-frequency active inductorless low-pass filter circuit provided in this embodiment form a biquadratic low-pass filter through the main transconductance amplifier circuit and the equivalent RLC load circuit, and filter the input differential signal in the way of equivalent inductance, avoiding the large area occupied by the use of inductors and reducing the occupied area of the filter; through the positive output circuit and the negative output circuit, the loss of the filtered signal reflected back is small, the impedance matching is good, and at the same time the insertion loss is small and the transmission characteristic is good, having a high out-of-band rejection characteristic; through the cross-coupling structure, the second capacitor C2, the collector left resistor RCL and the collector right resistor RCR, an equivalent inductance is constructed, so that the biquadratic low-pass filter has good linearity and can be used as an anti-aliasing filter at the front end of a high-speed data converter; by adopting a left-right symmetric fully differential structure for the biquadratic low-pass filter to process the input signal in the same way at the same time, the distortion degree of the output signal of the filter circuit is small and the fidelity degree is good; based on the four-stage high-frequency active inductorless low-pass filter circuit of the biquadratic low-pass filter, the stopband attenuation is large and the filtering effect is good, and high-frequency filtering with a signal frequency greater than 8 GHz can be realized.

[0138] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A dual second-order low-pass filter, characterized in that, The double second-order low-pass filter includes a main transconductance amplifier circuit, an equivalent RLC load circuit, a positive output circuit, a negative output circuit, and a bias current source circuit; The positive and negative input terminals of the main transconductance amplifier circuit are used to receive the input differential signal; the positive output terminal and the negative output terminal of the main transconductance amplifier circuit are respectively connected to the positive input terminal and the negative input terminal of the equivalent RLC load circuit; The positive output terminal and the negative output terminal of the equivalent RLC load circuit are respectively connected to the input terminal of the positive output circuit and the input terminal of the negative output circuit; the output terminals of the positive output circuit and the negative output circuit are used to output the differential signal; The bias current source circuit is used to provide bias current sources for the main transconductance amplifier circuit, the equivalent RLC load circuit, the positive output circuit, and the negative output circuit respectively.

2. The biquadratic low-pass filter according to claim 1, wherein The main transconductance amplifier circuit includes a current negative feedback left resistor REL, a current negative feedback right resistor RER, a first left transistor Q1L, and a first right transistor Q1R; The bases of the first left transistor Q1L and the first right transistor Q1R are respectively the positive input terminal and the negative input terminal of the main transconductance amplifier circuit; the collectors of the first left transistor Q1L and the first right transistor Q1R are respectively the positive output terminal and the negative output terminal of the main transconductance amplifier circuit; The emitter of the first left transistor Q1L is connected to one end of the current negative feedback left resistor REL, and the emitter of the first right transistor Q1R is connected to one end of the current negative feedback right resistor RER; The other ends of the current negative feedback left resistor REL and the current negative feedback right resistor RER are connected to each other for accessing the bias current source.

3. The dual second-order low-pass filter according to claim 2, characterized in that, The equivalent RLC load circuit includes a first capacitor C1, a second capacitor C2, a collector left resistor RCL, a collector right resistor RCR, and a cross-coupled structure; The cross-coupled structure is used to convert the second capacitor C2 from a capacitor to an inductor using a positive feedback impedance converter, and includes two input terminals and two output terminals; a first capacitor C1 is connected between the two input terminals, and at the same time, they are respectively used as the positive input terminal and the negative input terminal of the equivalent RLC load circuit; A second capacitor C2 is connected between the two output terminals, and at the same time, they are respectively used as the positive output terminal and the negative output terminal of the equivalent RLC load circuit; The two output terminals are also respectively grounded through the collector left resistor RCL and the collector right resistor RCR.

4. The dual second-order low-pass filter according to claim 3, wherein, The cross-coupled structure includes a second left transistor Q2L and a second right transistor Q2R; The emitters of the second left transistor Q2L and the second right transistor Q2R are respectively the two input terminals of the cross-coupled structure; The collectors of the second left transistor Q2L and the second right transistor Q2R are respectively the two output terminals of the cross-coupled structure; The base and the collector of the second left transistor Q2L are cross-connected to the collector and the base of the second right transistor Q2R.

5. The dual second-order low-pass filter according to claim 4, wherein The collector left resistor RCL and the collector right resistor RCR are the same; The second left transistor Q2L and the second right transistor Q2R are the same; The first left transistor Q1L and the first right transistor Q1R are the same; The current negative feedback left resistor REL and the current negative feedback right resistor RER are the same.

6. The dual second-order low-pass filter according to claim 1, characterized in that The positive output circuit includes a fourth left transistor Q4L, a fifth left transistor Q5L, and a sixth left transistor Q6L; The collector of the fourth left transistor Q4L is grounded, and the base of the fourth left transistor Q4L is the input terminal of the positive output circuit; the emitter of the fourth left transistor Q4L is connected to both the collector and the base of the fifth left transistor Q5L; The emitter of the fifth left transistor Q5L is connected to both the collector and the base of the sixth left transistor Q6L, and is also the output terminal of the positive output circuit; The emitter of the sixth left transistor Q6L is used to connect to a bias current source.

7. The dual second-order low-pass filter according to claim 6, wherein The negative output circuit includes a fourth right transistor Q4R, a fifth right transistor Q5R, and a sixth right transistor Q6R; The collector of the fourth right transistor Q4R is grounded, and the base of the fourth right transistor Q4R is the input terminal of the negative output circuit; the emitter of the fourth right transistor Q4R is connected to both the collector and the base of the fifth right transistor Q5R; The emitter of the fifth right transistor Q5R is connected to both the collector and the base of the sixth right transistor Q6R, and is also the output terminal of the negative output circuit; The emitter of the sixth right transistor Q6R is used to connect to a bias current source.

8. The dual second-order low-pass filter according to claim 6, characterized in that, The bias current source circuit includes a seventh left transistor Q7L, a seventh right transistor Q7R, a third transistor Q3, a first bias left resistor R1L, a first bias right resistor R1R, and a second resistor R2; The collectors of the seventh left transistor Q7L, the seventh right transistor Q7R, and the third transistor Q3 respectively output a bias current source for the positive output circuit, the main transconductance amplifier circuit, and the negative output circuit; The bases of the seventh left transistor Q7L, the seventh right transistor Q7R, and the third transistor Q3 are respectively connected to a bias voltage; The emitters of the seventh left transistor Q7L, the seventh right transistor Q7R, and the third transistor Q3 are respectively connected to the power supply voltage through the first bias left resistor R1L, the first bias right resistor R1R, and the second resistor R2.

9. The biquadratic low-pass filter according to any one of claims 1-8, characterized in that, The first left transistor Q1L, the first right transistor Q1R, the second left transistor Q2L, the second right transistor Q2R, the third transistor Q3, the fourth left transistor Q4L, the fourth right transistor Q4R, the fifth left transistor Q5L, the fifth right transistor Q5R, the sixth left transistor Q6L, the sixth right transistor Q6R, the seventh left transistor Q7L, and the seventh right transistor Q7R all adopt DHBT transistors with an indium phosphide substrate.

10. A high-frequency active inductorless low-pass filter circuit, characterized in that, The high-frequency active inductance-free low-pass filter circuit includes an input buffer unit, a first-order biquadratic low-pass filter, a second-order biquadratic low-pass filter, a third-order biquadratic low-pass filter, a fourth-order biquadratic low-pass filter, and an output buffer unit connected in series in sequence; The input buffer unit is used to receive the differential signal to be filtered; The first-order biquadratic low-pass filter, the second-order biquadratic low-pass filter, the third-order biquadratic low-pass filter, and the fourth-order biquadratic low-pass filter are biquadratic low-pass filters according to any one of claims 1-9, and are used to filter the differential signal to be filtered in sequence; The output buffer unit is used to output the filtered differential signal.

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