Filtered self-mixer

Abstract

Provided in the present disclosure is a filtered self-mixer, comprising: an input signal end, an energy detection circuit unit, a bias voltage unit, a coupling branch unit and a micro-electro-mechanical resonator branch, wherein the input signal end is configured to receive a wake-up signal and an interference signal to serve as input signals; the energy detection circuit unit comprises at least one CMOS transistor, and is configured to perform frequency mixing on the input signals by means of a secondary effect and output a baseband signal; the bias voltage unit is configured to provide a gate voltage of the CMOS transistor, so as to adjust a channel impedance of the CMOS transistor; the coupling branch unit is disposed between the input signal end and the energy detection circuit unit, and is configured to couple the input signals to a drain electrode or source electrode of the CMOS transistor in the energy detection circuit unit; and the micro-electro-mechanical resonator branch is disposed between the input signal end and the bias voltage unit. Different gate signals can be outputted at different frequencies to adjust a secondary effect, thereby filtering out an interference signal from input signals.

Description

Filtered Self-Mixer Technical Field

[0001] The present disclosure relates to the technical field of radio frequency wireless communications, and in particular to a filtering self-mixer for waking up a receiver. Background Art

[0002] The wake-up receiver can monitor the channel with extremely low power consumption. When the wake-up receiver receives the wake-up signal, it wakes up the main receiver, thereby reducing the standby power consumption of the wireless communication system.

[0003] With the advancement of wireless communication technology, wake-up receivers require lower power consumption, higher sensitivity, and enhanced interference rejection. To eliminate the high power consumption (>20 microwatts) introduced by the oscillator, low-power wake-up receivers often use a self-mixing architecture to downconvert the RF signal, thereby reducing system power consumption to below microwatts. However, existing self-mixers downconvert all input signals within the previous stage's passband to baseband. The self-mixing output spectra of the interference and signal alias in the baseband and become indistinguishable. Therefore, traditional low-power wake-up receivers have difficulty suppressing interference signals within the previous stage's passband. Their interference rejection capabilities rely on the previous stage's passband bandwidth and out-of-band rejection.

[0004] The RF passband bandwidth of the wake-up receiver is primarily determined by the matching or filtering network. Matching networks based on off-chip high-Q inductors have low losses, low power consumption, and high sensitivity. However, their relative fractional bandwidth is large (around 10%), resulting in poor anti-interference capabilities. To reduce the system bandwidth, a filter based on a microelectromechanical resonator can be inserted into the inductive matching network, or a matching network centered around an off-chip RF microelectromechanical resonator can be used. Thanks to the high Q of the microelectromechanical resonator (>1000), the system's relative fractional bandwidth can be significantly reduced (to approximately 0.5%). However, its out-of-band suppression (approximately 20dB) is insufficient to suppress larger out-of-band interfering signals. Furthermore, due to the high losses of the MEMS resonator, its power consumption and sensitivity are inferior to those of the inductive matching network.

[0005] In summary, the anti-interference capability of traditional low-power wake-up receivers depends on the bandwidth and out-of-band suppression of the preceding filter matching network. However, the bandwidth and out-of-band suppression capabilities of the current filter matching network are insufficient, and the existing self-mixer structure cannot provide filtering, thus limiting the anti-interference performance of the wake-up receiver.

[0006] Summary of the Invention

[0007] The present disclosure provides a filter self-mixer configured to improve the anti-interference performance of a wake-up receiver. The filter self-mixer includes: an input signal terminal, an energy detection circuit unit, a bias voltage unit, a coupling branch unit, and a micro-electromechanical resonator branch.

[0008] The input signal end is configured to receive a wake-up signal and an interference signal as input signals; the energy detection circuit unit includes at least one CMOS tube, which is configured to mix the input signal through a secondary effect and output a baseband signal; the bias voltage unit is configured to provide a gate voltage of the CMOS tube to adjust the channel impedance of the CMOS tube; the coupling branch unit is arranged between the input signal end and the energy detection circuit unit, and couples the input signal to the drain or source of the CMOS tube in the energy detection circuit unit; the micro-electromechanical resonator branch is arranged between the input signal end and the bias voltage unit, and can output different gate signals at different frequencies to adjust the secondary effect, thereby filtering out the interference signal in the input signal.

[0009] Optionally, the energy detection circuit is a triode type energy detection circuit, and the CMOS tube in the energy detection circuit unit is selected from an N-type CMOS tube and a P-type CMOS tube.

[0010] Optionally, the bias voltage unit includes at least one bias voltage branch, and each bias voltage branch includes a bias voltage source and a bias resistor connected in sequence.

[0011] Optionally, the coupling branch unit includes at least one coupling branch, each coupling branch includes a coupling capacitor connected to the input signal terminal, and the coupling capacitor is connected to the drain or source of the corresponding CMOS tube.

[0012] Optionally, the MEMS resonator branch includes a MEMS resonator and a DC blocking capacitor. One end of the MEMS resonator is connected to the input signal terminal, and the other end is connected to the gate of the CMOS transistor. The DC blocking capacitor is connected to the MEMS resonator and is configured to isolate the DC level of the CMOS transistor.

[0013] Optionally, the relative fractional bandwidth of the filtering self-mixer is less than 0.5%, and the out-of-band suppression capability is greater than 40 dB; and the operating frequency of the filtering self-mixer is the anti-resonance frequency of the micro-electromechanical resonator.

[0014] Optionally, when the frequency of the interference signal in the input signal is far away from the anti-resonance frequency, the microelectromechanical resonator is equivalent to an equivalent capacitor. The capacitance of the equivalent capacitor is adjusted by adjusting the geometric structure of the resonator to adjust the size of the gate signal coupled to the gate of the CMOS tube, so that the gate and drain of the transistor or the secondary effects of the drain cancel each other out, thereby not outputting a baseband signal.

[0015] Optionally, the type of the MEMS resonator is selected from a thin film bulk acoustic wave resonator, a transverse vibration piezoelectric resonator, a bulk acoustic wave resonator, a surface acoustic wave resonator, a Lamb wave resonator, a shear piezoelectric resonator, and a quartz crystal resonator.

[0016] Optionally, the CMOS tube arrangement in the energy detection circuit unit includes a single-stage arrangement, a multi-stage cascade arrangement or a pseudo-differential multi-stage cascade arrangement.

[0017] Optionally, the bias voltage source provides a gate DC bias voltage through a gate bias circuit, or provides a gate DC bias voltage through a drain or source of a transistor.

[0018] The filtered self-mixer disclosed in the present invention utilizes the different impedance characteristics of a microelectromechanical resonator at different frequencies to implement narrowband filtering on the self-mixer, thereby improving the anti-interference capability of the wake-up receiver; by offsetting the quadratic effects of the transistor gate and drain, extremely high out-of-band suppression is achieved, thereby improving the wake-up receiver's suppression of out-of-band interference; the filtered self-mixer has the characteristics of narrowband and high out-of-band suppression, so that the anti-interference performance of the wake-up receiver based on the filtered self-mixer no longer depends on the matching network of the previous stage; therefore, the matching network can adopt a topology structure and circuit parameters with higher bandwidth but lower loss, thereby improving the sensitivity of the wake-up receiver without reducing the anti-interference capability; the filtered self-mixer operates at the anti-resonance frequency of the microelectromechanical resonator. Since the Q value of the anti-resonance frequency of the RF microelectromechanical resonator is higher than the Q value of the resonant frequency, compared with the filtering method operating at the resonant frequency of the microelectromechanical resonator, the filtering method disclosed in the present invention has a higher Q value, a narrower passband, and better anti-interference capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG1 is a circuit diagram of a filtered self-mixer according to an embodiment of the present disclosure.

[0020] FIG. 2 is a circuit diagram of a conventional self-mixer.

[0021] Reference numerals:

[0022] 10: Energy detection circuit unit;

[0023] 11, 13: N-type CMOS tube;

[0024] 12, 14: P-type CMOS tube;

[0025] 21: micro-electromechanical resonator;

[0026] 22: DC blocking capacitor;

[0027] C1, C2, C C : coupling capacitor;

[0028] R B1 、R B2 : bias resistor;

[0029] V GN、 V GP : bias voltage source;

[0030] VC: common mode level;

[0031] V ed ,out: baseband output signal. DETAILED DESCRIPTION

[0032] The embodiments of the present disclosure will be further described below with reference to the accompanying drawings.

[0033] FIG1 is a circuit diagram of a filtered self-mixer according to an embodiment of the present disclosure.

[0034] The present disclosure provides a filter self-mixer, wherein the CMOS transistor included in the filter self-mixer is configured to provide a secondary effect, self-mixing the input signal; the micro-electromechanical resonator changes its impedance at different frequencies, so that the filter self-mixer has narrowband and high out-of-band suppression filtering characteristics; the coupling capacitor couples the input signal to the corresponding CMOS transistor; the bias resistor biases the gate voltage of the transistor; and the DC blocking capacitor is configured to isolate the DC level of different transistors. This makes the filter self-mixer of the present disclosure have a low passband bandwidth (<0.5%) and extremely high out-of-band suppression capability (>40dB). Its operating frequency is the anti-resonance frequency of the filter.

[0035] In the process of implementing the present disclosure, the inventors found that the existing self-mixer structure (a typical four-stage self-mixer structure as shown in FIG2 ) is coupled to the capacitor C C The AC input signal is input to the drain of the CMOS tube of the energy detection circuit unit, and the secondary effect of the weak inversion region transistor is used for mixing to generate the corresponding baseband output signal (V ed ,out), thereby mixing the input signal to baseband. The gate of the transistor is connected to an appropriate gate voltage (V GN 、V GP ) to adjust the transistor's channel resistance to match that of the preceding circuit. Within the preceding circuit's passband, the coupling capacitor's impedance is significantly smaller than the transistor's channel resistance, creating an equivalent AC short circuit between the input resistor and the transistor's drain. Consequently, any signal within the preceding circuit's passband will be mixed by the CMOS transistor and output as a baseband signal. Consequently, existing self-mixers lack filtering capabilities. Furthermore, because the out-of-band rejection of the MEMS resonator's filter matching network is limited, wake-up receivers based on existing self-mixers cannot effectively suppress high-power out-of-band interference signals.

[0036] Therefore, the present disclosure provides a filtered self-mixer having both relatively low passband bandwidth (<0.5%) and extremely high out-of-band rejection capability (>40 dB).

[0037] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0038] In an embodiment of the present disclosure, a filtered self-mixer is provided. As shown in FIG1 , the filtered self-mixer includes: an input signal terminal IN, an energy detection circuit unit 10, a bias voltage unit, a coupling branch unit, and a microelectromechanical resonator branch. The input signal terminal IN is configured to receive a wake-up signal and an interference signal as input signals; the energy detection circuit unit 10 includes at least one CMOS transistor, preferably 30 to 50 CMOS transistors. FIG1 shows four CMOS transistors, namely, an N-type CMOS transistor 11, a P-type CMOS transistor 12, an N-type CMOS transistor 13, and a P-type CMOS transistor 14, which are sequentially connected. The energy detection circuit unit 10 is configured to mix the input signal through the secondary effect of the CMOS tube and output a baseband signal; the bias voltage unit is configured to provide the gate voltage of the CMOS tube to adjust the channel impedance of the CMOS tube; the coupling branch unit is arranged between the input signal terminal and the energy detection circuit unit, and couples the input signal to the drain or source of the CMOS tube in the energy detection circuit unit. As shown in Figure 1, the input signal is coupled to the drain of the four CMOS tubes through the coupling capacitor C1 and the coupling capacitor C2 respectively; the micro-electromechanical resonator branch is arranged between the input signal terminal IN and the bias voltage unit and the energy detection circuit unit 10, and can output different gate signals at different frequencies to adjust the secondary effect and filter out the interference signal in the input signal. A coupling capacitor C is also connected between the signal output terminal OUT and the source of the N-type CMOS tube 11. C The source of the N-type CMOS tube 11 and the P-type CMOS tube 12 are connected to a coupling capacitor C C The source of the P-type CMOS transistor 14 is connected to a common-mode voltage VC.

[0039] According to an embodiment of the present disclosure, the energy detection circuit is a triode-type energy detection circuit. The CMOS transistors in the energy detection circuit unit are selected from N-type CMOS transistors and P-type CMOS transistors. The CMOS transistors in the energy detection circuit unit are arranged in a single-stage configuration, a multi-stage cascade configuration, or a pseudo-differential multi-stage cascade configuration. When both N-type and P-type CMOS transistors are present, the N-type and P-type CMOS transistors are connected alternately, for example, in an NPNP or PNPN configuration.

[0040] According to an embodiment of the present disclosure, the bias voltage unit includes at least one bias voltage branch, each bias voltage branch including a bias voltage source and a bias resistor connected in sequence. As shown in FIG1 , the bias voltage unit includes two bias voltage branches, namely, a bias voltage source V for providing gate voltage to two N-type CMOS transistors 11 and 13. GN and the bias voltage source V GN The connected bias resistor R B1 And the bias voltage source V that provides gate voltage to two P-type CMOS tubes 12 and 14 GP and the bias voltage source V GP The connected bias resistor R B2 .

[0041] According to an embodiment of the present disclosure, the coupling branch unit includes at least one coupling branch, each coupling branch including a coupling capacitor connected to the input signal terminal, which is connected to the drain or source of the corresponding CMOS transistor. As shown in Figure 1, the coupling branch unit includes two coupling branches, one of which has one end connected to the input signal terminal IN and the other end connected to the drains of N-type CMOS transistor 11 and P-type CMOS transistor 12 via coupling capacitor C1; the other coupling branch has one end connected to the input signal terminal IN and the other end connected to the drains of N-type CMOS transistor 13 and P-type CMOS transistor 14 via coupling capacitor C2.

[0042] According to an embodiment of the present disclosure, the MEMS resonator branch includes a MEMS resonator 21 and a DC blocking capacitor 22. One end of the MEMS resonator 21 is connected to the input signal terminal IN, and the other end is connected to the gate of a CMOS transistor. As shown in FIG1 , the other end of the MEMS resonator 21 is connected to the gates of N-type CMOS transistors 11 and 13. The DC blocking capacitor 22 has one end connected to the MEMS resonator 21 and one end connected to the gates of the CMOS transistors, and is configured to isolate the DC level of the CMOS transistors. As shown in FIG1 , the other end of the DC blocking capacitor 22 is connected to the gates of P-type CMOS transistors 12 and 14.

[0043] According to the embodiment of the present disclosure, the relative fractional bandwidth of the filter self-mixer is less than 0.5%, and the out-of-band suppression capability is greater than 40 dB; the operating frequency of the filter self-mixer is the anti-resonance frequency of the micro-electromechanical resonator.

[0044] According to the embodiment of the present disclosure, when the frequency of the interference signal in the input signal is far away from the anti-resonance frequency of the micro-electromechanical resonator 21, the micro-electromechanical resonator 21 is equivalent to an equivalent capacitor. By adjusting the geometric structure of the resonator to adjust the capacitance of the equivalent capacitor, the size of the gate signal coupled to the gate of the CMOS tube is adjusted, so that the gate and drain of the transistor or the secondary effects of the drain cancel each other out, thereby not outputting a baseband signal.

[0045] According to an embodiment of the present disclosure, the type of the MEMS resonator 21 is selected from a thin film bulk acoustic wave resonator, a transverse vibration piezoelectric resonator, a bulk acoustic wave resonator, a surface acoustic wave resonator, a Lamb wave resonator, a shear piezoelectric resonator, and a quartz crystal resonator.

[0046] According to the embodiment of the present disclosure, the bias voltage source (V GN 、V GP ) can provide a gate DC bias voltage through a gate bias circuit, or provide a gate DC bias voltage through the drain or source of the transistor.

[0047] According to an embodiment of the present disclosure, as shown in FIG1 , the number of stages of the filter self-mixer is 4 (i.e., the number of cascaded CMOS tubes is 4). In actual use, other stages may be used, preferably 30 or 40 stages, or a pseudo-differential cascade method may be used). A micro-electromechanical resonator 21 is introduced between the gate and drain of the CMOS tube, and the channel resistance of the transistor is adjusted and the DC is isolated by a bias resistor and a DC blocking capacitor. The RF micro-electromechanical resonator 21 exhibits a high-impedance characteristic near the anti-resonance frequency, and the filter self-mixer is equivalent to a traditional self-mixer. Outside the anti-resonance frequency, the impedance of the micro-electromechanical resonator decreases, which reduces the input impedance of the self-mixer, destroys the matching condition with the previous stage, and reduces the input signal size of the self-mixer. Therefore, for input signals of the same size, the output signal generated by the input at the anti-resonance frequency is greater than that at other frequencies, and the self-mixer achieves a filtering effect. Since the Q value of the micro-electromechanical resonator at the anti-resonance frequency is high, a lower passband bandwidth can be obtained. At frequencies far from the antiresonance frequency, the resonator acts as a capacitor. Adjusting the resonator's geometry adjusts the capacitance of this equivalent capacitor. Adjusting the capacitance adjusts the signal coupled to the CMOS transistor gate, canceling out the secondary effects of the transistor gate and drain, eliminating baseband output signals. Therefore, input signals far from the antiresonance frequency produce virtually no output signal.

[0048] The aforementioned filtered self-mixer has a low passband bandwidth (<0.5%) and extremely high out-of-band rejection (>40dB). Its operating frequency is the filter's anti-resonance frequency. Simulations of the output of normalized input signals of varying frequencies demonstrate that the filtered self-mixer achieves high-Q filtering with high out-of-band rejection while also maintaining self-mixing. This improves the wake-up receiver's anti-interference capability, sensitivity, and robustness.

[0049] In summary, the present disclosure provides a filtered self-mixer that, by introducing a microelectromechanical resonator into the self-mixer circuit, down-converts the input signal while achieving excellent filtering performance (bandwidth < 0.5%, out-of-band rejection > 50dB), thereby improving the anti-interference performance of the wake-up receiver.

[0050] The specific embodiments of the present disclosure described above do not limit the scope of protection of the present disclosure. Any other corresponding changes and modifications made based on the technical concept of the present disclosure should be included in the scope of protection of the claims of the present disclosure.

Claims

1. A filtering self-mixer, comprising: An input signal terminal, configured to receive a wake-up signal and an interference signal as input signals; An energy detection circuit unit composed of at least one CMOS tube is configured to mix an input signal through a secondary effect and output a baseband signal; A bias voltage unit, configured to provide a gate voltage of the CMOS tube to adjust the channel impedance of the CMOS tube; A coupling branch unit is arranged between the input signal terminal and the energy detection circuit unit, and couples the input signal to the drain or source of the CMOS tube in the energy detection circuit unit; as well as The micro-electromechanical resonator branch is arranged between the input signal terminal and the bias voltage unit, and can output different gate signals at different frequencies to adjust the secondary effect and filter out interference signals in the input signal.

2. The filtered self-mixer according to claim 1, wherein: The energy detection circuit is a triode type energy detection circuit, and the CMOS tube in the energy detection circuit unit is selected from an N-type CMOS tube and a P-type CMOS tube.

3. The filter self-mixer according to claim 2, wherein: The bias voltage unit includes at least one bias voltage branch, and each bias voltage branch includes a bias voltage source and a bias resistor connected in sequence.

4. The filtered self-mixer according to claim 2, wherein: The coupling branch unit includes at least one coupling branch, each coupling branch includes a coupling capacitor connected to an input signal terminal, and the coupling capacitor is connected to a drain or source of a corresponding CMOS tube.

5. The filtered self-mixer according to claim 4, wherein: The micro-electromechanical resonator branch comprises: A micro-electromechanical resonator, one end of which is connected to the input signal terminal, and the other end of which is connected to the gate of the CMOS tube; and The DC blocking capacitor, connected to the micro-electromechanical resonator, is configured to isolate the DC level of the CMOS tube.

6. The filter self-mixer according to claim 1, wherein the relative fractional bandwidth is less than 0.5%, and the out-of-band suppression capability is greater than 40 dB; and the operating frequency of the filter self-mixer is the anti-resonance frequency of the micro-electromechanical resonator.

7. According to the filtered self-mixer of claim 1, when the frequency of the interference signal in the input signal is far away from the anti-resonance frequency, the micro-electromechanical resonator is equivalent to an equivalent capacitor, and the capacitance of the equivalent capacitor is adjusted by adjusting the geometric structure of the resonator to adjust the size of the gate signal coupled to the gate of the CMOS tube, so that the gate and drain of the transistor or the secondary effects of the drain cancel each other out, thereby not outputting a baseband signal.

8. The filtered self-mixer according to claim 5, wherein: The type of the micro-electromechanical resonator is selected from a thin film bulk acoustic wave resonator, a lateral vibration piezoelectric resonator, a bulk acoustic wave resonator, a surface acoustic wave resonator, a Lamb wave resonator, a shear piezoelectric resonator, and a quartz crystal resonator.

9. The filtered self-mixer according to claim 1, wherein: The CMOS tube arrangement form in the energy detection circuit unit includes a single-stage form, a multi-stage cascade form or a multi-stage cascade form of a pseudo-differential form.

10. The filtered self-mixer according to claim 3, wherein: The bias voltage source provides a gate DC bias voltage through a gate voltage bias circuit, or provides a gate DC bias voltage through a drain or source of a transistor.

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