Differential high-pass filter inductor switching method and device

Abstract

The invention relates to the technical field of power line carrier communication interference resistance, in particular to a differential high-pass filter inductor switching method and device. Comprising the following steps; providing at least one fixed capacitor C and an adjustable inductor L; the inductance value of the inductor L connected to the circuit is switched through the electronic switch to adjust the cut-off frequency of the differential high-pass filter, so that the cut-off frequency is aligned with the power spectrum of an interference signal. Setting the statistical time of the average packet receiving success rate of the receiver as T; according to the working frequency band, the filters are sequentially accessed every time interval T, and the average packet receiving success rate corresponding to the filters is obtained; selecting a filter access parameter corresponding to the maximum average packet receiving success rate as an optimal filter parameter; according to the invention, the fixed filter is configured to be the programmable filter, and the cut-off frequency is aligned with the interference power spectrum, so that the anti-interference application range of the receiver is expanded.

Description

Technical Field

[0001] The present invention relates to the technical field of power line carrier communication anti-interference, and in particular to a differential high-pass filter inductance switching method and device. Background Art

[0002] Open channels are prone to external interference, and anti-interference is a prominent technical problem faced by open channel communication. Power lines are the transmission channels of power carrier communication. They are closely coupled with the external electromagnetic environment, and all electrical equipment are connected in parallel to the power line network. Various noise currents generated by electrical equipment during operation can leak into the power line channel, seriously interfering with power line carrier communication, compressing the coverage of power line carrier communication, and reducing the success rate of meter reading. The power interference in power lines is mainly concentrated in the lower frequency band, and the interference power spectrum is mostly distributed below 2MHz. In order to ensure the smooth progress of power meter reading networking, it is necessary to select a suitable transmission frequency band according to the distribution of the interference power spectrum. The receiver sets a pre-filter that matches the working frequency band to suppress the channel interference amplitude to a sufficiently low level to prevent the receiver from being blocked by strong interference or the linear dynamic range of the receiver from being compressed, thereby ensuring that the receiver demodulation end has sufficient available signal-to-noise ratio.

[0003] Power line meter reading often encounters strong interference on the power lines, which greatly reduces the data transmission throughput and causes network interruption in severe cases. The existing solutions are: 1) increase the average output power, 2) avoid the frequency band with high interference power spectrum, 3) adjust the built-in filter bandwidth of the receiver front-end chip, and 4) increase the relay.

[0004] like Figure 1 The figure shows a common power line carrier receiver interface block diagram. The interface between the power line carrier communication receiver and the power line channel includes: a coupling transformer and an off-chip filter; the off-chip filter is composed of a cascade of an L / C high-pass filter and an L / C low-pass filter to form a bandpass filter, which limits the communication spectrum to the passband of the bandpass filter. The power spectrum of power line interference is mainly concentrated in the low-frequency band. The hardware anti-interference ability of the receiver is mainly borne by the high-pass filter. The off-chip L / C high-pass filter adopts a differential transmission mode. The basic circuit is as follows Figure 2As shown. In order to suppress external interference, the best receiver should align the stop band of the pre-filter with the power spectrum of the interference, and the pass band should be able to adapt to the spectrum of the useful signal. If the low-end cutoff frequency of the high-pass filter is fixed and cannot be adjusted, the application range of the receiver against external interference will be very limited. If the power spectrum of the external interference is widened and exceeds the cutoff frequency of the high-pass filter, the receiver will be blocked by the strong interference, and the amplifier will enter a nonlinear state, resulting in serious distortion. The off-chip high-pass filter is the first protective barrier against interference, and the on-chip active high-pass filter is the second protective barrier against interference, which clears the dynamic range for the subsequent low-noise amplifier. The premise for the normal operation of the active filter is that the active device is in a linear state. In order to prevent the subsequent amplifier from generating serious nonlinear distortion and prevent the receiver from being blocked, the cutoff frequency of the off-chip high-pass filter should be programmable and configurable, showing sufficient suppression ability against strong interference, and ensuring that the on-chip active filter operates in the linear region.

[0005] The above four methods have played a decisive role in practical applications and improved the success rate of meter reading. Nevertheless, with the development of society, the power consumption is getting larger and larger, the types of power-consuming equipment are becoming more and more complex, the interference amplitude is getting stronger and stronger, and the interference power spectrum distribution is getting wider and wider. Under such circumstances, the technical means currently used are difficult to cope with the emergence of strong interference, and network paralysis still occurs from time to time. Therefore, resisting strong interference has become an unavoidable technical problem for power line carrier communication. Summary of the invention

[0006] The purpose of the present invention is to solve the problems existing in the background technology and propose a differential high-pass filter inductance switching method and device. The present invention configures the access inductance of the off-chip high-pass filter according to the working frequency band and external interference, thereby suppressing the interference; after the electronic switch is turned off, the adjustable filter is equivalent to the fixed filter, and when there is no external interference, the receiving sensitivity of the receiver will basically not be reduced.

[0007] The technical solution of the present invention is a differential high-pass filter inductance switching method, comprising the following steps:

[0008] Providing at least one fixed capacitor C and an adjustable inductor L;

[0009] The cutoff frequency of the differential high-pass filter is adjusted by switching the inductance value of the inductor L connected to the circuit through an electronic switch so as to align it with the power spectrum of the interference signal.

[0010] Set the statistical time of the receiver's "average packet receiving success rate" to T;

[0011] According to the working frequency band, the filters are connected in sequence at each interval T to obtain the "average packet reception success rate" corresponding to the filter;

[0012] The filter access parameters corresponding to the maximum value of Average Packet Receiving Success Rate are the optimal filter parameters.

[0013] Preferably, the switching of the inductor L is achieved through a fully differential symmetrical circuit to maintain impedance balance at both ends of the differential signal and prevent common-mode interference introduced by impedance imbalance.

[0014] Preferably, the electronic switch is arranged at a symmetrical point of the differential circuit, so that when the electronic switch is switched, only common-mode noise is introduced without generating differential-mode noise.

[0015] Preferably, the number and switching mode of the electronic switches are dynamically adjusted according to the power spectrum of the external interference and the corresponding operating frequency band.

[0016] A differential high-pass filter inductor switching device uses the above method to switch the inductor in the access circuit, including an initial high-pass filter, a first inductor switching module and a first inductor switching module;

[0017] Among them, the electronic switch used to switch the inductor circuit is realized by a high-frequency triode;

[0018] Two switches can realize four states; four cutoff frequencies can be switched by controlling two GPIOs.

[0019] Preferably, in each inductor switching circuit, two identical inductors are symmetrically distributed on both sides of C and E of the switching transistor;

[0020] When the transistor is turned on, the two inductors are connected in series and then connected to the two ends of the differential signal, in parallel with the initial inductance, so that the inductance of the filter is reduced and the cut-off frequency of the filter is changed.

[0021] Preferably, the initial high-pass filter comprises: capacitors C1, C2 and inductor L5;

[0022] The first inductor switching module includes: transistors Q1, Q3, inductors L1, L2, resistors R1, R3, R5, R7, R9, R11, R13 and capacitor C5;

[0023] The second inductor switching module includes transistors Q2 and Q4, inductors L3 and L4, resistors R2, R4, R6, R8, R10, R12, R14 and capacitor C6.

[0024] Preferably, when GPIO_1 outputs a high level V H , Q3 is saturated and turned on, Q1 is turned on accordingly, and the emitter current I E1 From VCC1 through R1, L1 into the base, the collector current I C1 From VCC1 through R2 and L2 into the base, the base current I B1 =I E1 +IC1 , and I E1 ≈I C1 ;

[0025] After Q1 is turned on, the AC resistance between the collector and emitter is very small, L1 and L2 are connected in series, connected to both ends of the differential input, and connected in parallel with L5. The filter cutoff frequency is determined by C1, C2, and L5 / / (L1+L2);

[0026] When GPIO_1 outputs a low level V L , Q3 is turned off, the base voltage of Q1 is pulled up to VCC2 by R7, Q1 is turned off, and when the instantaneous value of the signal voltage at the Vin+ terminal is Vp <VCC2+V BE(ON) -VCC1, Q1 can still remain cut off, and will not cause obvious distortion of the differential signal;

[0027] Under the influence of the two control quantities GPIO_1 and GPIO_2, the inductance value of the differential loop presents four states: L5, L5 / / (L1+L2), L5 / / (L3+L4), L5 / / (L1+L2) / / (L3+L4), corresponding to four cutoff frequencies respectively.

[0028] Preferably, after Q1 is turned on, R9 becomes the load of the middle point A of the differential inductors L1 and L2;

[0029] For the common mode, V+ / V- are equal in magnitude and polarity, so after Q1 is turned on, the base current limiting resistor R9 is the load of the symmetrical midpoint A, and equally divides the current from V+ / V-;

[0030] For the differential mode, V+ / V- are equal in magnitude and opposite in polarity. Therefore, after Q1 is turned on, the base becomes the symmetrical point of L1 and L2, and the midpoint A is equivalent to the AC GND. The base current limiting resistor R9 has no effect on the differential mode.

[0031] Preferably, when the transistor is turned on, a certain amount of noise will be injected into the PN junction of the transistor; since Q1 is at the symmetrical midpoint of the inductors L1 and L2, the impedances on both sides are equal, and the noise I_n flows to V+ and V-, I_n+=I_n-=I_n / 2;

[0032] Since the receiver adopts differential transmission, if the input impedance is Rin, the receiver input signal voltage is Vin=(Vout+)–(Vout-), and the input noise voltage V_n=[(I_n+)-(I_n-)]*Rin=0.

[0033] Compared with the prior art, the present invention has the following beneficial technical effects:

[0034] 1. The present invention configures the fixed filter as a programmable filter and aligns the cutoff frequency with the power spectrum of the interference to expand the anti-interference application range of the receiver.

[0035] 2. The present invention adopts a fully differential symmetrical circuit and uses an electronic switch for switching, which can maintain the impedance balance at both ends of the differential signal and prevent the introduction of common mode interference due to impedance imbalance.

[0036] 3. In the present invention, the switching switch is placed at the symmetrical point of the differential circuit, that is, the equivalent GND point of the differential signal. Switching only introduces common-mode noise and does not generate differential-mode noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a block diagram of the interface of a power line carrier receiver in the prior art;

[0038] Figure 2 It is a basic differential L / C high-pass filter in the prior art;

[0039] Figure 3 A simplified circuit diagram of an improved solution of this embodiment;

[0040] Figure 4 A specific circuit diagram of the improved solution of this embodiment;

[0041] Figure 5 This is the common-mode equivalent circuit of the switching circuit (Q1 is turned on) of this embodiment;

[0042] Figure 6 is the differential mode equivalent circuit of the switching circuit (Q1 is turned on) of this embodiment;

[0043] Figure 7 An equivalent circuit for electronic switching noise injection in this embodiment;

[0044] Figure 8 4 is a circuit diagram for implementing an embodiment of the present invention. DETAILED DESCRIPTION

[0045] Example 1

[0046] A differential high-pass filter inductance switching method proposed by the present invention comprises the following steps:

[0047] Providing at least one fixed capacitor C and an adjustable inductor L;

[0048] The cutoff frequency of the differential high-pass filter is adjusted by switching the inductance value of the inductor L connected to the circuit through an electronic switch so as to align it with the power spectrum of the interference signal.

[0049] The statistical time of the receiver's "average packet reception success rate" is set to T; according to the working frequency band, the filter is accessed in sequence at every interval T to obtain the "average packet reception success rate" corresponding to the filter; the corresponding filter access parameter when the maximum value of the "average packet reception success rate" is selected is the optimal filter parameter.

[0050] It should be noted that the evaluation criteria for the best filter vary in different applications, and the methods used should also be adapted to local conditions. Within the conditions allowed by the system, when the output performance of the receiver maximizes the core technical indicators by switching the filter, the connected filter is the best filter.

[0051] The switching of the inductor L is achieved through a fully differential symmetrical circuit to maintain the impedance balance at both ends of the differential signal and prevent common-mode interference introduced by impedance imbalance; the electronic switch is set at the symmetrical point of the differential circuit; when the electronic switch is switched, only common-mode noise is introduced without generating differential-mode noise; the switching mode of the electronic switch is dynamically adjusted according to the power spectrum of the external interference and the corresponding working frequency band.

[0052] like Figure 3 As shown, in order to reduce the complexity of the circuit, a compromise method is adopted. On the basis of the basic differential L / C high-pass filter, the fixed capacitor C remains unchanged, and the cutoff frequency of the high-pass filter is adjusted by switching the inductor L to adapt to the power spectrum of the external interference and the corresponding working frequency band.

[0053] Example 2

[0054] like Figure 4 As shown, a differential high-pass filter inductor switching circuit proposed by the present invention, compared with embodiment 1, in this embodiment, the electronic switch used for switching the inductor is realized by a high-frequency transistor, and two switching switches can realize four states, so that two GPIOs can be used to switch four cut-off frequencies. In each inductor switching branch, two identical inductors are symmetrically distributed on both sides of C and E of the switching transistor. When the transistor is turned on, the two inductors are connected in series and then connected to the two ends of the differential signal, and are connected in parallel with the initial inductor L5, so that the inductance of the filter is reduced, thereby changing the cut-off frequency of the filter.

[0055] The initial high-pass filter includes: capacitors C1, C2 and inductor L5; the first inductor switching module includes: transistors Q1, Q3, inductors L1, L2, resistors R1, R3, R5, R7, R9, R11, R13 and capacitor C5; the second inductor switching module includes: transistors Q2, Q4, inductors L3, L4, resistors R2, R4, R6, R8, R10, R12, R14 and capacitor C6.

[0056] When GPIO_1 outputs a high level V H , Q3 is saturated and turned on, Q1 is turned on accordingly, and the emitter current IE1 From VCC1 through R1, L1 into the base, the collector current I C1 From VCC1 through R2 and L2 into the base, the base current I B1 =I E1 +I C1 , and I E1 ≈I C1 ;

[0057] After Q1 is turned on, the AC resistance between the collector and emitter is very small, L1 and L2 are connected in series, connected to both ends of the differential input, and connected in parallel with L5. The filter cutoff frequency is determined by C1, C2, and L5 / / (L1+L2);

[0058] When GPIO_1 outputs a low level V L , Q3 is turned off, the base voltage of Q1 is pulled up to VCC2 by R7, Q1 is turned off, and when the instantaneous value of the signal voltage at the Vin+ terminal is Vp <VCC2+V BE(ON) -VCC1, Q1 can still remain cut off, and will not cause obvious distortion of the differential signal;

[0059] Under the influence of the two control quantities GPIO_1 and GPIO_2, the inductance value of the differential loop presents four states: L5, L5 / / (L1+L2), L5 / / (L3+L4), L5 / / (L1+L2) / / (L3+L4), corresponding to four cutoff frequencies respectively.

[0060] In this embodiment, after Q1 is turned on, R9 becomes the load of the middle point A of the differential inductors L1 and L2;

[0061] like Figure 5 As shown, for the common mode, V+ / V- are equal in magnitude and polarity, so after Q1 is turned on, the base current limiting resistor R9 is the load of the symmetrical midpoint A, and equally divides the current from V+ / V-;

[0062] like Figure 6 As shown, for the differential mode, V+ / V- are equal in magnitude and opposite in polarity. Therefore, after Q1 is turned on, the base becomes the symmetrical point of L1 and L2, and the midpoint A is equivalent to the AC GND. The base current limiting resistor R9 has no effect on the differential mode.

[0063] like Figure 7 As shown, when the transistor is turned on, the PN junction of the transistor will inject a certain amount of noise; since Q1 is at the symmetrical midpoint of the inductors L1 and L2, the impedances on both sides are equal, and the noise I_n flows to V+ and V-, I_n+=I_n-=I_n / 2;

[0064] Since the receiver adopts differential transmission, if the input impedance is Rin, the receiver input signal voltage is Vin = (Vout+) - (Vout-), and the input noise voltage V_n = [(I_n+) - (I_n-)] * Rin = 0

[0065] The solution of this embodiment is introduced below using a specific circuit structure;

[0066] Circuit structure as Figure 8 As shown:

[0067] When a single inductor is switched, the current of R1 and R2 is 1.4mA; when both inductors are switched, the current of R1 and R2 is 2.3mA, and the differential load resistance RL is 300Ω.

[0068] -6dB cutoff frequency: 0.8MHz@GPIO_1=L,GPIO_2=L;

[0069] 1.6MHz@GPIO_1=H, GPIO_2=L;

[0070] 2.4MHz@GPIO_1=L, GPIO_2=H;

[0071] 2.6MHz@GPIO_1=H, GPIO_2=H.

[0072] Out-of-band suppression: 40dB / 100kHz, @GPIO_1=L, GPIO_2=L;

[0073] 50dB / 100kHz, @GPIO_1=H, GPIO_2=L;

[0074] 55dB / 100kHz, @GPIO_1=L, GPIO_2=H;

[0075] 60dB / 100kHz, @GPIO_1=H, GPIO_2=H.

[0076] Distortion: -60dB / 3MHz, 2Vp, @GPIO_1=L, GPIO_2=L

[0077] -45dB / 3MHz, 2Vp, @GPIO_1=H, GPIO_2=L;

[0078] -50dB / 3MHz, 2Vp, @GPIO_1=L, GPIO_2=H;

[0079] -60dB / 3MHz, 2Vp, @GPIO_1=H, GPIO_2=H.

[0080] Best filter selection:

[0081] HPF0 is recorded as @GPIO_1=L, GPIO_2=L; HPF1 is recorded as @GPIO_1=H, GPIO_2=L; HPF2 is recorded as @GPIO_1=L, GPIO_2=H; HPF3 is recorded as @GPIO_1=H, GPIO_2=H.

[0082] The network success rate and meter reading success rate are the core technical indicators of the power meter reading system. The channel status of each meter box on the same phase of the power line is different, and the performance of power interference is also quite different. The meter reading system specifies the working frequency band according to the power spectrum distribution of power interference, so the interference suppression ability of the filter almost determines the communication success rate. Because the data frame contains CRC check bits, if the CRC check is successful, the packet is received correctly, so the statistical quantity "average packet reception success rate" can be used to measure the network communication effect.

[0083] Steps: (1) Set the statistical time of "average packet receiving success rate" to T; (2) According to the working frequency band, at every interval T, connect the filters in the order of HPF0, HPF1, HPF2, and HPF3, so that the "average packet receiving success rate" corresponding to each filter is obtained; (3) When the success rate reaches the maximum value, the corresponding filter HPF i is the optimal filter.

[0084] In this embodiment, the triode is used as the symmetry point, and the branch inductance is decomposed into two series inductors, which are respectively located on both sides of the triode C and E poles, to maintain the symmetry of the two ends of the differential. After the triode is turned on, the base bias resistor has no effect on the differential signal; the PN junction noise is offset at the differential end and will not increase the input noise of the receiver. According to the working frequency band and external interference, the access inductance of the off-chip high-pass filter is configured to suppress interference; after the electronic switch is turned off, the adjustable filter is equivalent to the fixed filter, and when there is no external interference, the receiving sensitivity of the receiver will basically not be reduced.

[0085] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited thereto, and various changes can be made within the knowledge scope of technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A differential high-pass filter inductor switching method, characterized in that: The steps include: Providing at least one fixed capacitor C and an adjustable inductor L; The inductance value of the inductor L connected to the circuit is switched by an electronic switch to adjust the cutoff frequency of the differential high-pass filter so as to align it with the power spectrum of the interference signal; Set the statistical time of the receiver's "average packet receiving success rate" to T; According to the working frequency band, the filters are connected in sequence at each interval T to obtain the "average packet reception success rate" corresponding to the filter; The filter access parameters corresponding to the maximum value of "Average Packet Receiving Success Rate" are the optimal filter parameters.

2. A differential high-pass filter inductance switching method according to claim 1, characterized in that: The switching of the inductor L is achieved through a fully differential symmetrical circuit to maintain impedance balance at both ends of the differential signal and prevent common-mode interference introduced by impedance imbalance.

3. A differential high-pass filter inductance switching method according to claim 1, characterized in that: The electronic switch is arranged at a symmetrical point of the differential circuit so that only common mode noise is introduced when the electronic switch is switched, without generating differential mode noise.

4. The method for switching inductance of a differential high-pass filter according to claim 1, characterized in that: The switching mode of the electronic switch is dynamically adjusted according to the power spectrum of the external interference and the corresponding operating frequency band.

5. A differential high-pass filter inductor switching device, using the method described in any one of claims 1 to 4 to switch the inductor in the connected circuit, characterized in that: It includes an initial high-pass filter, a first inductor switching module and a first inductor switching module; Among them, the electronic switch used to switch the inductor circuit is realized by a high-frequency triode; Two switches can realize four states; four cutoff frequencies can be switched by controlling two GPIOs.

6. The differential high-pass filter inductor switching device according to claim 5, characterized in that: In each inductor switching circuit, two identical inductors are symmetrically distributed on both sides of C and E of the switching transistor; When the transistor is turned on, the two inductors are connected in series and then connected to the two ends of the differential signal, in parallel with the initial inductance, so that the inductance of the filter is reduced and the cut-off frequency of the filter is changed.

7. The differential high-pass filter inductor switching device according to claim 5, characterized in that: The initial high-pass filter includes: capacitors C1, C2 and inductor L5; The first inductor switching module includes: transistors Q1, Q3, inductors L1, L2, resistors R1, R3, R5, R7, R9, R11, R13 and capacitor C5; The second inductor switching module includes transistors Q2 and Q4, inductors L3 and L4, resistors R2, R4, R6, R8, R10, R12, R14 and capacitor C6.

Images