Mixer circuit with low spurious output

Abstract

The invention discloses a mixer circuit with low spurious output. The mixer circuit comprises an intermediate frequency balun, a radio frequency balun, a diode mixing core, a radio frequency matching network, a local oscillator matching network and a filtering matching network, an intermediate-frequency signal is input from an unbalanced port of the intermediate-frequency balun, is converted into a pair of intermediate-frequency differential signals through the intermediate-frequency balun, and then is connected with a pair of endpoints C and D of the diode mixing core; a local oscillator signal is fed into the other pair of endpoints A and B of the diode mixing core after passing through the local oscillator matching network; a radio frequency signal obtained after mixing of a local oscillator signal and an intermediate frequency signal is taken out from a pair of endpoints A and B of the diode frequency mixing core, passes through a series capacitor C2 and a series capacitor C3 and then is connected to the radio frequency balun, a pair of radio frequency differential signals are converted into single-ended signals through the radio frequency balun, and finally the radio frequency signal is output after passing through the radio frequency matching network. The spurious suppression performance of the receiver is improved, and the design difficulty of a radio frequency link is reduced.

Description

Technical Field

[0001] The invention relates to a mixer circuit with low stray output, belonging to the technical field of radio frequency microwave integrated circuits. Background Art

[0002] With the continuous development of satellite communication technology, the system's requirements for satellite-borne microwave transceivers are becoming higher and higher, mainly reflected in lower power consumption, smaller size and weight, higher harmonic suppression, etc. The performance of the mixer, as a frequency conversion device in the RF microwave transceiver system, directly affects the performance of the entire RF front end. According to whether there is DC power consumption, mixers can be divided into active mixers and passive mixers; according to the circuit topology, mixers can be divided into single-ended, single-balanced and double-balanced mixers. At present, the mixers in satellite-borne transceivers basically use MMIC chips based on the passive double-balanced mixer structure, which have the characteristics of small size and high reliability.

[0003] In communication satellite transponders, an up-conversion mode in which the local oscillator operating frequency is much lower than the input intermediate frequency and the output RF frequency often occurs. For this frequency conversion mode, when a traditional passive double-balanced mixer is used, due to the low operating frequency of the local oscillator, the local oscillator signal actually needs to be fed from the intermediate frequency port of the mixer, and the intermediate frequency signal is input from the local oscillator port of the mixer. When the local oscillator signal is fed from the center tap of the RF balun into the diode stack, it will have a greater impact on the balance of the RF balun, thereby increasing the spurious components of the mixer output.

[0004] In addition, for the above-mentioned frequency conversion mode, the higher harmonics of the local oscillator signal and the mixed components of the higher harmonics of the local oscillator and the input intermediate frequency signal are often very close to the output RF frequency, or directly fall within the output RF operating frequency band, making it extremely difficult or impossible for the filter to suppress the local oscillator harmonic noise, thereby affecting the performance of the receiver. Summary of the invention

[0005] The technical problem solved by the present invention is: for the up-conversion mode in which the local oscillator frequency is much lower than the RF output frequency, when the traditional passive double-balanced mixer structure is used, the local oscillator higher harmonics and mixing clutter are close to the output frequency, resulting in difficulty in suppressing the mixing spurious waves of the receiver. A mixer circuit with low spurious output is proposed, which improves the spurious suppression performance of the receiver and reduces the design difficulty of the RF link.

[0006] The technical solution of the present invention is:

[0007] A mixer circuit with low spurious output includes: an intermediate frequency balun, a radio frequency balun, a diode mixing core, a radio frequency matching network, a local oscillator matching network and a filter matching network;

[0008] The intermediate frequency signal is input from the unbalanced port of the intermediate frequency balun, and after being converted into a pair of intermediate frequency differential signals by the intermediate frequency balun, is connected to a pair of terminals C and D of the diode mixer core; the local oscillator signal passes through the local oscillator matching network and is fed into another pair of terminals A and B of the diode mixer core;

[0009] The RF signal after mixing the local oscillator signal and the intermediate frequency signal is taken out from a pair of terminals A and B of the diode mixer core, and then connected to the RF balun after passing through series capacitors C2 and C3 respectively. The RF balun converts a pair of RF differential signals into single-ended signals, and finally the RF signal is output after passing through the RF matching network.

[0010] Furthermore, the diode mixing core includes four Schottky diodes D1, D2, D3, and D4 of exactly the same size. The four diodes are connected end to end to form a ring, that is, the anode of diode D1 is connected to the cathode of diode D4, the anode of diode D2 is connected to the cathode of diode D1, the anode of diode D3 is connected to the cathode of diode D2, and the anode of diode D4 is connected to the cathode of diode D3.

[0011] Further, the intermediate frequency balun includes three ports, the intermediate frequency signal is input from port 1 of the intermediate frequency balun, that is, the unbalanced port, and the intermediate frequency balun converts the intermediate frequency signal into a pair of differential signals and outputs them from port 2 and port 3, which are respectively connected to a pair of endpoints C and D of the mixing core;

[0012] The endpoint C refers to the endpoint between the anode of the diode D1 and the cathode of the diode D4; the endpoint D refers to the endpoint between the anode of the diode D3 and the cathode of the diode D2.

[0013] Furthermore, another pair of endpoints A and B of the diode mixing core are respectively: endpoint A refers to the endpoint between the anode of the diode D2 and the cathode of the diode D1; endpoint B refers to the endpoint between the anode of the diode D4 and the cathode of the diode D3.

[0014] Furthermore, the function of the capacitors C2 and C3 is to allow only the mixed RF signal to enter the RF balun and prevent the local oscillator signal from leaking into the RF balun, thereby improving the mixing efficiency.

[0015] Furthermore, the local oscillator matching network includes: inductors L2, L3, L4 and capacitor C4; the local oscillator signal is connected to one end of the inductor L4, the other end of the inductor L4 is connected to the terminal B of the diode mixing core through the inductor L2, and the other end of the inductor L4 is also connected to the terminal A of the diode mixing core through the inductor L3; at the same time, the other end of the inductor L4 is also grounded through the capacitor C4.

[0016] Further, the radio frequency matching network includes capacitors C5, C6 and inductor L5;

[0017] The RF balun converts a pair of RF differential signals into single-ended signals, and then outputs the signals through capacitors C5 and C6 connected in series. Meanwhile, capacitors C5 and C6 are grounded through inductor L5.

[0018] Furthermore, the mixer circuit is packaged as a chip and implemented using a GaAs pHEMT process.

[0019] Furthermore, the chip has three interfaces, namely a local oscillator signal input interface, an intermediate frequency signal input interface, and a radio frequency signal output interface.

[0020] The beneficial effects of the present invention compared with the prior art are:

[0021] (1) The present invention proposes a mixer with low spurious output for up-conversion application modes where the local oscillator signal is much lower than the RF output frequency. Compared with the traditional passive double-balanced mixer, the local oscillator signal is directly fed into the diode mixing core through a filter matching network instead of being fed into the local oscillator signal from the center tap of the RF balun. Therefore, the balance of the RF balun is not destroyed, thereby greatly improving the spurious suppression of the RF output signal.

[0022] (2) A matching network is added to the output end of the RF balun of the present invention, which improves the matching of the RF end on the one hand, and can suppress the spurious components at the low frequency end of the RF output frequency to a certain extent on the other hand;

[0023] (3) The local oscillator matching network of the present invention improves the impedance matching between the fundamental wave and the harmonic wave at the local oscillator end, thereby reducing the local oscillator harmonic component after diode mixing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A topological diagram of a mixer circuit with low spurious output proposed by the present invention;

[0025] Figure 2 This is a topological diagram of a conventional double-balanced mixer circuit, in which the local oscillator port and the intermediate frequency port of the present invention are interchangeably used.

[0026] Figure 3 (a) is the simulation result 1 of the mixer output spectrum in the embodiment which does not adopt the structure of the present invention, wherein the intermediate frequency input frequency is 13 GHz, the power is -15 dBm, the local oscillator frequency is 5.45 GHz, and the power is 13 dBm;

[0027] Figure 3 (b) is the simulation result 1 of the output spectrum of the mixer using the structure of the present invention in the embodiment, wherein the intermediate frequency input frequency is 13 GHz, the power is -15 dBm, the local oscillator frequency is 5.45 GHz, and the power is 13 dBm;

[0028] Figure 4(a) is the simulation result 2 of the mixer output spectrum in the embodiment without using the structure of the present invention, wherein the intermediate frequency input frequency is 15 GHz, the power is -15 dBm, the local oscillator frequency is 5.7 GHz, and the power is 13 dBm;

[0029] Figure 4 (b) is the simulation result 2 of the mixer output spectrum using the structure of the present invention in the embodiment, wherein the intermediate frequency input frequency is 15 GHz, the power is -15 dBm, the local oscillator frequency is 5.7 GHz, and the power is 13 dBm. DETAILED DESCRIPTION

[0030] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0031] The present invention provides a mixer circuit with a special local oscillator signal feeding mode and low spurious output, such as Figure 1 As shown, it includes an intermediate frequency balun, an RF balun, a diode mixing core, an RF matching network, a local oscillator matching network and a filter matching network.

[0032] The intermediate frequency signal is input from the unbalanced port of the intermediate frequency balun, and after being converted into a pair of intermediate frequency differential signals by the intermediate frequency balun, is connected to a pair of terminals C and D of the diode mixer core; the local oscillator signal passes through the local oscillator matching network and is fed into another pair of terminals A and B of the diode mixer core;

[0033] The RF signal after mixing the local oscillator signal and the intermediate frequency signal is taken out from a pair of terminals A and B of the diode mixer core, and then connected to the RF balun after passing through series capacitors C2 and C3 respectively. The RF balun converts a pair of RF differential signals into single-ended signals, and finally the RF signal is output after passing through the RF matching network.

[0034] The diode mixing core includes four Schottky diodes D1, D2, D3, and D4 of exactly the same size, and the four diodes are connected end to end to form a ring, that is, the anode of the diode D1 is connected to the cathode of the diode D4, the anode of the diode D2 is connected to the cathode of the diode D1, the anode of the diode D3 is connected to the cathode of the diode D2, and the anode of the diode D4 is connected to the cathode of the diode D3;

[0035] The intermediate frequency balun includes three ports. The intermediate frequency signal is input from port 1 of the intermediate frequency balun. The intermediate frequency balun converts the intermediate frequency signal into a pair of differential signals and outputs them from port 2 and port 3, which are respectively connected to a pair of endpoints C and D of the Schottky diode mixing core; the endpoint C refers to the endpoint between the anode of the diode D1 and the cathode of the diode D4; the endpoint D refers to the endpoint between the anode of the diode D3 and the cathode of the diode D2.

[0036] The local oscillator signal passes through a local oscillator matching network composed of a series inductor L4, a parallel capacitor C4, and series inductors L2 and L3, and is connected to the other pair of terminals A and B of the Schottky diode mixer core respectively.

[0037] The other pair of endpoints A and B of the diode mixer core are respectively: endpoint A refers to the endpoint between the anode of the diode D2 and the cathode of the diode D1; endpoint B refers to the endpoint between the anode of the diode D4 and the cathode of the diode D3.

[0038] The local oscillator matching network includes: inductors L2, L3, L4 and capacitor C4; the local oscillator signal is connected to one end of the inductor L4, the other end of the inductor L4 is connected to the terminal B of the diode mixing core through the inductor L2, and the other end of the inductor L4 is also connected to the terminal A of the diode mixing core through the inductor L3; at the same time, the other end of the inductor L4 is also grounded through the capacitor C4.

[0039] After the local oscillator signal and the intermediate frequency signal enter the Schottky diode mixer core, the RF signal generated by the mixing is taken out from a pair of terminals A and B of the diode mixer core. After the two signals pass through the series capacitors C2 and C3 respectively, they are connected to the ports 2 and 3 of the RF balun. After the RF balun converts a pair of RF differential signals into single-ended signals, they are finally output after passing through the RF matching network composed of series capacitors C5, C6 and parallel inductor L5. The function of the capacitors C2 and C3 is to only allow the mixed RF signal to enter the RF balun, and prevent the local oscillator signal from leaking to the RF balun, thereby improving the mixing efficiency.

[0040] The RF matching network includes capacitors C5, C6 and inductor L5; the RF balun converts a pair of RF differential signals into single-ended signals, and then outputs the signals through capacitors C5 and C6 connected in series. Meanwhile, capacitors C5 and C6 are also grounded through inductor L5.

[0041] Preferably, the mixer is packaged as a chip and implemented using a GaAs pHEMT process including a Schottky diode, which has the advantages of small size, light weight, no need for debugging, and high reliability. The chip has three interfaces, namely, a local oscillator signal input interface, an intermediate frequency signal input interface, and a radio frequency signal output interface.

[0042] Example:

[0043] According to the above-mentioned mixer principle with special local oscillator signal feeding mode with low spurious output, the up-conversion mixer chip circuit indicators realized by using GaAs pHEMT process are as follows:

[0044] IF input frequency: 13GHz~15GHz

[0045] Local oscillator operating frequency: 5.4GHz~5.7GHz

[0046] LO input power: 13dBm

[0047] RF output frequency: 18.4GHz~20.7GHz

[0048] 3*LO power measured at RF port: ≤-39dBm

[0049] 4*LO power measured at RF port: ≤-50dBm

[0050] 6*LO-IF power measured at RF port: ≤-80dBm

[0051] Figure 3 to Figure 4 They are respectively the simulation results of the RF port output spectrum of the mixer chip according to the embodiment of the present invention, wherein Figure 3 (a) and Figure 4 (a) is the simulation result of the traditional structure mixer. The simulation adopts Figure 2 The topology shown in the figure has the local oscillator and intermediate frequency signal ports set to Figure 2 Ports in brackets ( Figure 2 is a circuit topology diagram of a conventional double-balanced mixer, in which the local oscillator port and the intermediate frequency port of the present invention are interchangeably used).

[0052] Figure 3 (b) and Figure 4 (b) is the simulation result of the mixer structure proposed by the present invention.

[0053] Among them, m1 is the RF (ie, LO+IF) output power value, m2 is the 6×LO-IF output power value, m3 is the 3×LO output power value, m4 is the 4×LO output power value, and m5 is the LO output power value.

[0054] It can be seen from the simulation results that for the up-conversion application mode where the local oscillator frequency is much lower than the output frequency, compared with the traditional passive double-balanced mixer, the mixer structure proposed by the present invention has a significant improvement in the suppression of the mixed spurious output, among which the local oscillator third harmonic output power is 15-20dB smaller than the traditional structure, the local oscillator fourth harmonic output power is 20-24dB smaller than the traditional structure, the 6×LO-IF output power closest to the RF output frequency is 20dB smaller than the traditional structure, and the local oscillator output power is 35dB smaller than the traditional structure. At the same time, it can be seen from the output spectrum simulation results that the mixer structure of the present invention has also improved the spurious output power of other frequencies to varying degrees.

[0055] In the embodiment of the present invention, the circuit structure is simple, the devices used are all planar circuits, and the GaAs process is used for integration. The mixer chip size is only 1.6mm*1.1mm*0.1mm, the reliability is high, and it can be easily integrated into the satellite receiver components for use.

[0056] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention are included in the protection scope of the present invention.

[0057] The undisclosed technologies in the present invention are common knowledge to those skilled in the art.

Claims

1. A mixer circuit with low spurious output, characterized in that include: IF balun, RF balun, diode mixer core, RF matching network, local oscillator matching network and filter matching network; The intermediate frequency signal is input from the unbalanced port of the intermediate frequency balun, and after being converted into a pair of intermediate frequency differential signals by the intermediate frequency balun, is connected to a pair of terminals C and D of the diode mixer core; the local oscillator signal passes through the local oscillator matching network and is fed into another pair of terminals A and B of the diode mixer core; The RF signal after mixing the local oscillator signal and the intermediate frequency signal is taken out from a pair of terminals A and B of the diode mixer core, and then connected to the RF balun after passing through series capacitors C2 and C3 respectively. The RF balun converts a pair of RF differential signals into single-ended signals, and finally the RF signal is output after passing through the RF matching network.

2. The mixer circuit with low spurious output according to claim 1, characterized in that: The diode mixing core includes four Schottky diodes D1, D2, D3, and D4 of exactly the same size. The four diodes are connected end to end to form a ring, that is, the anode of the diode D1 is connected to the cathode of the diode D4, the anode of the diode D2 is connected to the cathode of the diode D1, the anode of the diode D3 is connected to the cathode of the diode D2, and the anode of the diode D4 is connected to the cathode of the diode D3.

3. The mixer circuit with low spurious output according to claim 2, characterized in that: The intermediate frequency balun includes three ports. The intermediate frequency signal is input from port 1 of the intermediate frequency balun, that is, the unbalanced port. The intermediate frequency balun converts the intermediate frequency signal into a pair of differential signals and outputs them from port 2 and port 3, which are respectively connected to a pair of endpoints C and D of the mixing core. The endpoint C refers to the endpoint between the anode of the diode D1 and the cathode of the diode D4; the endpoint D refers to the endpoint between the anode of the diode D3 and the cathode of the diode D2.

4. The mixer circuit with low spurious output according to claim 1, characterized in that: The other pair of endpoints A and B of the diode mixer core are respectively: endpoint A refers to the endpoint between the anode of the diode D2 and the cathode of the diode D1; endpoint B refers to the endpoint between the anode of the diode D4 and the cathode of the diode D3.

5. The mixer circuit with low spurious output according to claim 1, characterized in that: The function of capacitors C2 and C3 is to allow only the mixed RF signal to enter the RF balun and prevent the local oscillator signal from leaking into the RF balun, thereby improving the mixing efficiency.

6. The mixer circuit with low spurious output according to claim 1, characterized in that: The local oscillator matching network includes: inductors L2, L3, L4 and capacitor C4; the local oscillator signal is connected to one end of the inductor L4, the other end of the inductor L4 is connected to the terminal B of the diode mixing core through the inductor L2, and the other end of the inductor L4 is also connected to the terminal A of the diode mixing core through the inductor L3; at the same time, the other end of the inductor L4 is also grounded through the capacitor C4.

7. The mixer circuit with low spurious output according to claim 1, characterized in that: The radio frequency matching network includes capacitors C5, C6 and inductor L5; The RF balun converts a pair of RF differential signals into single-ended signals, and then outputs the signals through capacitors C5 and C6 connected in series. Meanwhile, capacitors C5 and C6 are grounded through inductor L5.

8. The mixer circuit with low spurious output according to claim 1, characterized in that: The mixer circuit is packaged as a chip and is implemented using a GaAs pHEMT process.

9. The mixer circuit with low spurious output according to claim 8, characterized in that: The chip has three interfaces, namely a local oscillator signal input interface, an intermediate frequency signal input interface, and a radio frequency signal output interface.

10. The mixer circuit with low spurious output according to claim 8, characterized in that: The chip circuit indicators are as follows: IF input frequency: 13GHz~15GHz Local oscillator operating frequency: 5.4GHz~5.7GHz LO input power: 13dBm RF output frequency: 18.4GHz~20.7GHz 3*LO power measured at RF port: ≤-39dBm 4*LO power measured at RF port: ≤-50dBm 6*LO-IF power measured at the RF port: ≤-80dBm.

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