Low-power-consumption temperature-interference-resistant transmitter for wireless sensor network

Abstract

The invention provides a low-power-consumption temperature interference resistant transmitter for a wireless sensor network. The transmitter provides a stable reference current by temperature compensation of a beta multiplier reference circuit (BMR). Or stable reference current is provided directly through an off-chip circuit. Through combination of a current starvation type voltage-controlled oscillator (CSVCO) and a frequency locked loop (FLL), stable carrier frequency is realized under the condition of low power consumption. The negative temperature coefficient resistor integrated in the FLL further enhances the adaptability of the system to temperature change. The transmitter further comprises a buffer and a switched capacitor power amplifier (SCPA), and the switched capacitor power amplifier (SCPA) facilitates impedance matching with the antenna in a mode of activating part of units, and meanwhile loss is reduced. OOK modulation is realized by controlling the on-off state of the SCPA. According to the low-power-consumption temperature interference resistant transmitter, the power consumption is reduced, the temperature interference resistant capability of the carrier generator is remarkably improved, and the low-power-consumption temperature interference resistant transmitter has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to wireless sensor network technology, and particularly to a low-power temperature-interference-resistant transmitter for a wireless sensor network. Background Art

[0002] Wireless sensor networks are widely used in the field of environmental monitoring because of their real-time feedback capabilities. Such networks typically consist of sensor nodes, a base station, and related software. Figure 1 is a block diagram of a sensor node. The node faces many problems, among which the effects of power consumption and temperature are particularly significant. The node is usually powered by a battery, but due to the large number of deployments and complex environments, battery replacement is time-consuming and expensive. Among the various circuits of the node, the transceiver is the most power-consuming module, and its power consumption accounts for 51% to 80% of the total power consumption [1]. Therefore, it is crucial to design a low-power transceiver. In addition to power consumption, the sensor node needs to operate reliably at various temperatures. Temperature fluctuations can significantly affect circuit performance because many circuit parameters are functions of temperature, such as the threshold voltage of MOS transistors. To ensure that the data collected by the sensor node can be accurately transmitted to the base station, the carrier frequency of the transmitter must also remain stable when the temperature changes.

[0003] Currently, there have been many studies on low-power transmitters. To generate a stable carrier frequency, phase-locked loops are used in references [2, 3, 4, 5], etc. The power consumption of a phase-locked loop is usually between several hundred microwatts and several milliwatts, and the power consumption is relatively high. To reduce power consumption, references [6, 7, 8], etc. directly use a low-power oscillator to generate a carrier signal, but the influence of temperature changes on the carrier frequency is not solved. Manual adjustment is required after the temperature changes.

[0004] It should be noted that the information disclosed in the above background art section is only used for understanding the background of the present application, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0005] The main object of the present invention is to overcome the defects existing in the above background art, and to provide a low-power temperature-interference-resistant transmitter for a wireless sensor network.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A low-power temperature-interference-resistant transmitter for a wireless sensor network, comprising:

[0008] A reference circuit for providing a reference current. The reference circuit adopts a beta multiplier reference circuit (BMR), including an off-chip resistor and an on-chip resistor with a positive temperature coefficient to compensate for the influence of temperature and process variations on the current; or, without the reference circuit, a stable reference current is directly provided by an off-chip circuit.

[0009] A carrier generator, including a current-starved voltage-controlled oscillator (CSVCO) and a frequency-locked loop (FLL). The CSVCO is used to generate an oscillation signal at low power consumption, and the FLL is used to monitor and adjust the frequency of the CSVCO in real time, and a resistor with a negative temperature coefficient is used for temperature compensation to enhance the anti-temperature interference ability of the carrier generator.

[0010] A buffer for isolating the carrier generator and the power amplifier and improving the driving ability of the carrier generator.

[0011] A switched-capacitor power amplifier (SCPA) for amplifying the signal power and implementing OOK modulation by controlling the on / off of the SCPA. Among them, the SCPA obtains the optimal impedance close to the antenna impedance by activating some units to further reduce the loss on the impedance matching network.

[0012] Further, the reference circuit further includes a resistor with a positive temperature coefficient for compensating for the increase in the bias current caused by the increase in temperature.

[0013] Further, the FLL includes a frequency-voltage converter (FVC) for converting the change in the CSVCO frequency into a corresponding voltage change.

[0014] Further, the FVC circuit utilizes the relationship between the equivalent switched-capacitor resistor and the frequency, and uses the current flowing through the equivalent switched-capacitor resistor to generate a frequency-related voltage.

[0015] Further, the carrier generator further includes an amplifier for adjusting the frequency of the oscillation signal generated by the CSVCO. The amplifier dynamically adjusts the control voltage Vc by comparing the reference voltage and the voltage generated by the FVC, thereby realizing stable control of the CSVCO frequency; this amplifier is a part of the frequency-locked loop FLL for ensuring the frequency stability of the oscillator.

[0016] Further, the buffer is composed of three-stage inverters for improving the driving ability of the carrier generator and isolating the carrier generator and the switched-capacitor power amplifier SCPA; the buffer receives the signal from the carrier generator, amplifies the signal by inverting it stage by stage to enhance the driving ability of the signal, and isolates it to supply the power amplifier.

[0017] Further, the SCPA includes a plurality of basic power amplification units, realizes OOK modulation by controlling the on / off of the MOSFET control unit circuit, and the SCPA can activate some or all of the units according to the output power requirement; preferably, the number of units is 3 or more.

[0018] Further, the optimal impedance of the SCPA is obtained through a simulation tool.

[0019] Further, the operating frequency of the transmitter is 433 MHz, and the output power is about 0 dBm.

[0020] Further, the transmitter adopts OOK modulation, and by introducing a frequency-locked loop FLL and a temperature compensation mechanism, and using the comparison between the reference voltage and the voltage generated by the frequency-voltage converter FVC, dynamically adjusts the control voltage of the CSVCO to achieve the stability of the carrier frequency.

[0021] Further, the transmitter further includes a matching network for impedance matching with the antenna, and obtains the optimal impedance close to the antenna impedance by activating some SCPA units to further reduce the loss on the impedance matching network.

[0022] The present invention has the following beneficial effects:

[0023] The present invention innovatively designs a low-power and temperature-interference-resistant transmitter, which is particularly suitable for wireless sensor networks. Through the collaborative work of the reference circuit, carrier generator, buffer, and switched-capacitor power amplifier (SCPA), the transmitter achieves the stability of the carrier frequency at a lower power consumption, while effectively reducing the influence of temperature fluctuations on the carrier frequency. This design not only improves the performance of the transmitter, but also significantly reduces its power consumption, making it have significant advantages in application scenarios such as wireless sensor networks.

[0024] First, the transmitter of the present invention preferably adopts a beta multiplier reference circuit (BMR). By combining an off-chip resistor and an on-chip resistor with a positive temperature coefficient, the influence of temperature and process variations on the current is effectively compensated. In addition, a stable reference current can also be directly provided through an off-chip circuit. The design of the carrier generator includes a current-starved voltage-controlled oscillator (CSVCO) and a frequency-locked loop (FLL). The CSVCO generates an oscillation signal at low power consumption, while the FLL is responsible for real-time monitoring and adjusting the frequency of the CSVCO. A resistor with a negative temperature coefficient is used in the FLL for temperature compensation, significantly enhancing the anti-temperature interference ability of the carrier generator. In addition, through the buffer design with a three-stage inverter structure, not only is the driving ability of the carrier generator improved, but also effective isolation from the power amplifier is achieved. This helps to improve the signal integrity and stability for subsequent power amplification and modulation. The SCPA of the present invention facilitates impedance matching with the antenna by selectively controlling the activation of some units, thus significantly reducing the loss on the impedance matching network. In addition, this switch-type PA design of the SCPA has higher efficiency than traditional linear PAs, especially in low-power applications. The design of the SCPA allows for flexible activation of some or all units according to the output power requirement, improving the adaptability of the transmitter.

[0025] In summary, through a series of innovative designs, the present invention realizes the ability of the transmitter to resist temperature interference at low power consumption while maintaining the stability of the carrier frequency. These technical advantages enable the transmitter of the present invention to have broad application prospects in wireless communication systems such as wireless sensor networks, the Internet of Things, wearable devices, and smart homes, which require low power consumption and high clock accuracy.

[0026] Other beneficial effects in the embodiments of the present invention will be further described below. Description of the Drawings

[0027] Figure 1 It is a schematic diagram of a sensor node.

[0028] Figure 2 It is a system block diagram of the transmitter according to the embodiment of the present invention.

[0029] Figure 3 It is a circuit schematic diagram of the CSVCO according to the embodiment of the present invention.

[0030] Figure 4 It is a curve of the oscillation frequency of the CSVCO according to the embodiment of the present invention varying with the control voltage Vc.

[0031] Figure 5 It is a circuit schematic diagram of the FVC according to the embodiment of the present invention.

[0032] Figure 6 It is a circuit schematic diagram of the amplifier in the carrier generator according to the embodiment of the present invention.

[0033] Figure 7 This is the temperature characteristic of the equivalent resistance of the embodiment of the present invention.

[0034] Figure 8 This is the schematic diagram of the SCPA circuit of the embodiment of the present invention.

[0035] Figure 9 This is the power consumption of each part of the transmitter circuit of the embodiment of the present invention.

[0036] Figure 10 This is the variation of the carrier frequency with temperature in the embodiment of the present invention.

[0037] Figure 11 This is the capacitance-voltage relationship of varactors with different sizes in the embodiment of the present invention. Detailed implementation manners

[0038] The following makes a detailed description of the implementation manners of the present invention. It should be emphasized that the following description is merely exemplary and not intended to limit the scope of the present invention and its applications.

[0039] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, the connection can be for a fixing function or for a coupling or communicating function.

[0040] It should be understood that the orientation or positional relationship indicated by terms such as "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present invention.

[0041] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0042] Refer to Figures 2 to 8, an embodiment of the present invention provides a low-power anti-temperature interference transmitter for a wireless sensor network, including: a reference circuit for providing a reference current. The reference circuit adopts a beta multiplier reference circuit (BMR), including an off-chip resistor and an on-chip resistor with a positive temperature coefficient to compensate for the influence of temperature and process variations on the current; or, without the reference circuit, a stable reference current is directly provided by an off-chip circuit; a carrier generator, including a current-starved voltage-controlled oscillator (CSVCO) and a frequency-locked loop (FLL). The CSVCO is used to generate an oscillation signal at low power, and the FLL is used to monitor and adjust the frequency of the CSVCO in real time, and a resistor with a negative temperature coefficient is used for temperature compensation to enhance the anti-temperature interference ability of the carrier generator; a buffer for isolating the carrier generator and the power amplifier and improving the driving ability of the carrier generator; a switched-capacitor power amplifier (SCPA) for amplifying the signal power and implementing OOK modulation by controlling the on / off of the SCPA. Among them, the SCPA obtains an optimal impedance close to the antenna impedance by activating some units to further reduce the loss on the impedance matching network.

[0043] The focus of the present invention is to optimize the power consumption of the transmitter while improving the anti-temperature interference ability of the carrier of the transmitter. The present invention effectively reduces the power consumption of the carrier generator and reduces the influence of temperature fluctuations on the carrier frequency through three steps: compensating the reference circuit, introducing a frequency-locked loop (FLL), and performing temperature compensation on the FLL. The power amplifier (PA) is the most power-consuming module in the transmitter. In most literatures, a relatively complex modulation scheme is adopted, so a higher linearity requirement is imposed on the PA. OOK modulation is adopted in the present invention. The PA uses a switched-capacitor power amplifier (SCPA). The switched PA has higher efficiency than the linear PA, and the SCPA has more advantages in low-power applications [9, 10, 11].

[0044] In some embodiments, the transmitter realizes the stability of the carrier frequency of the transmitter at low power and reduces the influence of temperature fluctuations on the carrier frequency through the mutual cooperation of the reference circuit or the off-chip circuit providing the bias current, the carrier generator, the buffer, and the SCPA.

[0045] In some embodiments, the reference circuit further includes a resistor with a positive temperature coefficient. The function of this resistor is to compensate for the increase in the bias current caused by the increase in temperature, thereby improving the temperature stability of the transmitter.

[0046] Preferably, the FLL includes a frequency-voltage converter (FVC) that converts the change in the CSVCO frequency into a corresponding voltage change for frequency control.

[0047] In a further embodiment, the FVC circuit utilizes the relationship between the equivalent switched-capacitor resistance and the frequency, and a frequency-related voltage is generated by the current flowing through the equivalent switched-capacitor resistance. In addition, the carrier generator further includes an amplifier for adjusting the frequency of the oscillation signal generated by the CSVCO. The amplifier dynamically adjusts the control voltage Vc by comparing the reference voltage and the voltage generated by the FVC, thereby achieving stable control of the CSVCO frequency. The amplifier is part of a frequency-locked loop FLL for ensuring the frequency stability of the oscillator.

[0048] In some embodiments, the buffer is composed of three-stage inverters, which are used to improve the driving ability of the carrier generator and isolate the carrier generator and the power amplifier SCPA. The buffer receives the signal from the carrier generator, enhances the driving ability of the signal through step-by-step inverting amplification, and isolates it for supply to the power amplifier.

[0049] In some embodiments, the SCPA includes a plurality of basic power amplification units, and OOK modulation is achieved by controlling the on-off of the MOSFET control unit circuit. Moreover, the SCPA can activate some or all of the units according to the output power requirement. Preferably, the number of power amplification units is 3 or more. In addition, the optimal impedance of the SCPA is obtained through a simulation tool.

[0050] Preferably, the operating frequency of the transmitter is 433 MHz, and the output power is about 0 dBm. The transmitter preferably uses OOK modulation, and by introducing a frequency-locked loop FLL and a temperature compensation mechanism, the control voltage of the CSVCO is dynamically adjusted by comparing the reference voltage and the voltage generated by the frequency-voltage converter FVC to achieve the stability of the carrier frequency.

[0051] In some embodiments, the transmitter further includes a matching network for impedance matching with the antenna. By activating some SCPA units, the optimal impedance close to the antenna impedance is obtained to further reduce the loss on the impedance matching network.

[0052] Through the above design of the present invention, while maintaining low power consumption, the transmitter can effectively resist the influence of temperature changes on performance, and is suitable for application scenarios with high requirements for energy efficiency and stability such as wireless sensor networks.

[0053] The specific embodiments of the present invention and experimental verification are further described below.

[0054] The operating frequency of the transmitter is 433 MHz, and the output power is about 0 dBm. The system block diagram is as Figure 2As shown in the figure, the transmitter consists of four parts: a reference circuit, a carrier generator, a buffer, and an SCPA. The reference circuit provides a reference current for the system; the carrier generator generates a carrier signal with stable frequency and resistance to temperature fluctuations; the buffer isolates the carrier generator and the power amplifier and improves the driving ability of the carrier generator; the SCPA is used to amplify the power of the signal. An off-chip matching network is adopted in this design. The transmitter realizes OOK modulation by controlling the on / off of the SCPA.

[0055] The reference circuit adopts a Beta-Multiplier Reference (BMR) circuit. The calculation formula for the generated reference current is:

[0056]

[0057] where μ n represents the electron mobility, C ox represents the gate oxide capacitance per unit area, and (W / L) represents the width-to-length ratio of the MOS transistor. K represents that the width-to-length ratio of MN2 is K times that of MN1. Since the on-chip resistance is affected by the process, an off-chip resistor R I is added. Off-chip, the resistance value and voltage of R I can be measured, and R I can be adjusted to regulate the bias current to the designed value.

[0058] Figure 2 The system block diagram of the transmitter according to the embodiment of the present invention is shown.

[0059] The Current Starved Voltage Controlled Oscillator (CSVCO) in the carrier generator provides an oscillation signal at low power consumption. Figure 3 is the schematic diagram of the CSVCO according to the embodiment of the present invention. MP0 is a current source that replicates the current in the reference circuit. MN0 and MN1-MN4 form a group of current mirrors. MP1 and MP2-MP4 form another group of current mirrors. The circuit consists of three delay units connected end to end. Taking the first delay unit as an example, MP5 and MN5 form an inverter, and MP2 and MN2 limit the current in the delay unit. Assuming that there is a rising edge signal at the input of the first delay unit (i.e., the gates of MP5 and MN5), after three levels of inverting delay, a falling edge will appear at the input of the first delay unit, forming half a cycle of the oscillator. In the present invention, a frequency modulation capacitor is added to adjust the frequency of the oscillator. The frequency modulation capacitor uses a varactor diode. By adjusting the magnitude of the control voltage Vc, the capacitance can be changed, thereby changing the delay and ultimately changing the frequency of the oscillator. As Figure 4 shown in the variation curve of the oscillation frequency of the CSVCO with the control voltage Vc, the lower the Vc, the lower the frequency of the CSVCO oscillator.

[0060] Although at a fixed temperature, the control voltage Vc can be manually adjusted to obtain the target frequency of 433 MHz, the frequency will vary with temperature changes. There are mainly two reasons: First, the reference current is affected by temperature, and the generated current increases with the increase in temperature. As the current in the circuit increases, the frequency of the oscillator will become faster. Second, the circuit parameters of the CSVCO itself are affected by temperature. For example, circuit parameters such as the threshold voltage are functions of temperature. This design solves the problem of frequency variation with temperature through three steps. The first step is to use a positive temperature coefficient resistor Rptc to compensate the reference circuit; the second step is to introduce an FLL to monitor and adjust the frequency of the CSVCO in real time; the third step is to use a negative temperature coefficient resistor R ntc to compensate the FLL and further increase the anti-temperature interference ability. The following separately introduces these three steps.

[0061] The first step is to use a positive temperature coefficient resistor Rptc to compensate the reference circuit. The reason for the increase in the bias current with the increase in temperature can be obtained from Equation (1). The electron mobility is related to the concentration of impurities and temperature, etc. In the 65nm CMOS process adopted by the present invention, the electron mobility decreases with the increase in temperature. So as shown above Figure 2 the on-chip part of the resistor uses a positive temperature coefficient resistor Rptc. As the temperature increases, the resistance increases, which can, to a certain extent, inhibit the increase in current.

[0062] The second step is to introduce an FLL to monitor and adjust the frequency of the CSVCO in real time. The FLL consists of a carrier generator and a reference voltage Vref generation circuit. The function of the Frequency-to-Voltage Converter (FVC) in the carrier generator is: to convert the change in the CSVCO frequency into a corresponding voltage change. Figure 5 is the circuit schematic diagram of the FVC. The basic idea of the circuit is: to utilize the relationship between the equivalent switched-capacitor resistor R eq and the frequency f. The inverters composed of MP1, MN1 and MP2, MN2 generate two-phase clocks to control the on-off of two groups of switches composed of MN3, MP3 and MN4, MP4. The equivalent resistance R eq can be approximately expressed as:

[0063]

[0064] This equivalent resistance is inversely proportional to the frequency f of the CSVCO. The higher the input frequency, the smaller the equivalent resistance value. MP5 is a current source. The current flows through this frequency-dependent resistor, generating a frequency-dependent voltage. This kind of equivalence is equal on average. The circuit uses capacitor C2 for filtering to obtain a DC voltage.

[0065] Figure 5 The circuit schematic diagram of the FVC according to the embodiment of the present invention is shown. Figure 6 It is the schematic diagram of the amplifier in the carrier generator according to the embodiment of the present invention. The gate terminal of MP2 is the negative input terminal of the amplifier, and the gate terminal of MP3 is the positive input terminal. Changing the frequency of the CSVCO requires a control voltage Vc. This control voltage Vc is the output of the amplifier. The output is connected to the frequency modulation capacitor to adjust the frequency of the CSVCO. In Figure 2 , the current source MP3 copies the reference current, and the current flows through the resistors Rntc and R car to form the reference voltage Vref. This reference voltage is connected to the negative input terminal of the amplifier. The positive input terminal of the amplifier is connected to the output of the FVC circuit. Since the voltage generated by the FVC has some fluctuations, the output of the amplifier will also have small fluctuations. In Figure 6 , a capacitor C1 is added for filtering. Figure 2 In, the current source MP3 and Figure 5 the current source MP5 in have the same size and flow the same current. Denote this current as Id. So there is:

[0066] V ref = Id × (Rntc + R car ) (3)

[0067]

[0068] The process of the FLL stabilizing the frequency is as follows: Assume that the frequency of the oscillator is higher than the target value of 433 MHz. From Equation (2), it can be seen that the higher the frequency f, the smaller the equivalent resistance R eq . Substituting into Equation (4), the voltage Vinp is also lower. Since Vinp is connected to the positive input terminal of the amplifier, when this voltage is lower than V ref at the negative input terminal of the amplifier, the output voltage Vc of the amplifier will also become lower. As shown in Figure 4 before, when the control voltage Vc becomes lower, the frequency of the oscillator will gradually become lower. This process will continue until V ref = Vinp ends. Substituting this result into Equations (3) and (4), the frequency of the carrier can be obtained as:

[0069]

[0070] It can be seen from Equation (5) that the carrier frequency f car has nothing to do with the current Id, so the reference current does not need to be very accurate. Compared with circuit parameters such as the threshold voltage, the capacitor is less affected by temperature. By reasonably utilizing the temperature characteristics of the resistor, the influence of temperature can also be reduced. Therefore, after introducing the FLL, the stability of the frequency is significantly improved.

[0071] In the third step, temperature compensation is performed on the introduced FLL to further enhance the ability of the carrier generator to resist temperature interference. The on-chip capacitor C car has a negative temperature coefficient: as the temperature increases, its capacitance value will decrease. Combining with the calculation formula (5) of the carrier frequency, it is easy to misinterpret that in order to maintain the stability of the carrier frequency, the total resistance of R ntc and R car in series should have a positive temperature characteristic. However, in the previous analysis of the FVC circuit, the non-ideal characteristics of devices such as switches were not considered in the ideal model. According to Equation (2), ideally, the equivalent resistance Req should increase as the temperature increases. However, the actual situation is as Figure 7 shown, the equivalent resistance decreases as the temperature increases. When designing the circuit, after the capacitor C car and the carrier frequency are determined, the total resistance of R ntc and R car in series should be equal to the value of the equivalent resistance at the target frequency. Therefore, the total resistance of R ntc and R car in series should also have a negative temperature coefficient. Therefore, in the present invention, the on-chip part uses a resistor R ntc with a negative temperature coefficient for compensation. In addition, as can be seen from Figure 7 , the on-chip capacitor is greatly affected by the process. Under different process corners, the difference in the equivalent resistance is relatively large. Therefore, R car is placed off-chip, both to overcome the influence of the on-chip resistor by the process and to reduce the adverse effects brought by the capacitance deviation.

[0072] The buffer is composed of three-stage inverters. Figure 8 It is shown that the SCPA of the embodiment of the present invention consists of three units. OOK modulation is achieved by controlling the on-off of the unit circuit. Taking Unit 1 as an example, when the external input is a low level (i.e., sending "0", D 1 D 2 D 3 = 000), after passing through the inverter INV1, the output is a high level. The switch SW1 is composed of a PMOS transistor, so it is turned off. The drain terminals of MP1 and MN1 are at a low level. There is no output signal on the antenna. When the external input is a high level (i.e., sending "1", D 1 D 2 D 3= 100), the output of the inverter INV1 is at a low level and the switch SW1 is turned on. At this time, MN1 and MP1 form a class-D power amplifier. After the output of the CSVCO passes through a buffer, it is sent to the gate inputs of MN1 and MP1, and a square wave signal with the same frequency and opposite phase is obtained at the output end (i.e., the drain ends of MN1 and MP1). The resonant frequency of the capacitor C (C = C1 + C2 + C3) and the inductor L is the same as the fundamental frequency of the square wave, filtering out the fundamental frequency component of the square wave. After passing through the matching network, the filtering effect is further enhanced, and a more ideal sine wave can be obtained. Finally, the antenna radiates this sine wave signal. In this design, most of the time only unit 1 is activated. The designs of units 2 and 3 are mainly used in some relatively harsh environments and are activated only when a greater output power is required. The optimal impedance r opt The calculation formula for

[10] is:

[0073]

[0074] where N represents the total number of units, n represents the number of activated units, P out is the output power, and V DD is the supply voltage (1.8V in the present invention). Substituting the parameters into (6), the optimal impedance of 73Ω is obtained. Due to the influence of parasitic resistors and capacitors in the circuit, there will be some differences between the optimal impedance and the calculated value. In the present invention, the optimal impedance is obtained through simulation with a load-pull tool. The lower the output power of the transmitter, the lower the efficiency usually is

[12] . When units 2 and 3 are activated together, although the optimal impedance at this time is different from that when only unit 1 is activated, since the number of activated units increases and the output power increases, the transmitter efficiency also increases.

[0075] Figure 8 shows the schematic diagram of the SCPA circuit of the embodiment.

[0076] Experiments and effects:

[0077] Table 1 compares the transmitter of the present invention with the transmitters in the existing literature. The transmitter of the present invention has a higher data rate. Comparing the transmitters with similar output powers, the proposed transmitter has lower power consumption. Figure 9 shows the power consumption of each part of the circuit when only unit 1 is activated and the output power is 0.4dBm.

[0078] The reason why the transmitter proposed by the present invention has low power consumption is as follows: First, a carrier is generated with lower power consumption. The power consumption of the carrier generator (CSVCO + FVC + AMP) in the present invention is only 47.8 μW. While usually using a PLL to generate a carrier requires hundreds of microwatts or even milliwatts. Second, the present invention adopts OOK modulation and a lower carrier frequency. The OOK signal is quite special, with only two amplitudes, high and low, carrying information. The requirement for linearity is much lower. Therefore, a switching-type PA is adopted in this design. Compared with the traditional linear PA, the switching-type PA has higher efficiency. In addition to the type of PA, the matching network also affects the efficiency of the entire transmitter. The greater the difference between the optimal impedance and the antenna impedance (usually 50 Ω), the greater the loss of the matching network. In a linear PA, the optimal impedance is relatively large. For example, for a class A PA, when outputting 0 dBm power and using the 1.8 V voltage of the present invention, the optimal impedance is 1620 Ω, and the impedance transformation ratio is too large. While in the present invention, an SCPA is adopted, and by activating some units, the optimal impedance is obtained as 73 ohms. Because it is closer to the antenna impedance, the loss on the impedance matching network is reduced.

[0079] Table 1 Comparison of the performance of low-power transmitters

[0080]

[0081] 1 Post-simulation results

[0082] 2 Transmitter efficiency = output power / transmitter power consumption

[0083] Figure 9 The power consumption of each part of the circuit of the transmitter is shown.

[0084] Compared with the literature that directly uses an oscillator to generate a carrier, while reducing the power consumption, the present invention improves the ability of the carrier generator to resist temperature interference by 173 times. Figure 10It shows the stability of the carrier frequency of the proposed solution when the temperature changes. The red line in the figure represents no compensation, and only a fixed voltage is given to the frequency modulation capacitor of the CSVCO (similar to

[15] , manually adjusting the carrier frequency). As the temperature changes from 0 °C to 70 °C, the frequency changes from 383.2 MHz to 504.2 MHz, a change of 121 MHz. Since all data is displayed, the curve is not clear. Therefore, only the maximum and minimum values are marked for each curve. The proposed solution: First step, use a positive temperature coefficient resistor Rptc to compensate the reference circuit (the frequency modulation capacitor of the CSVCO is still given a fixed value). At this time, as shown by the blue line in the figure, the frequency changes from 398 MHz to 463.6 MHz, a change of 65.6 MHz. The frequency is much more stable. Second step, introduce FLL to monitor and adjust the frequency of the CSVCO in real time. The result is shown by the black dotted line in the figure, and the frequency changes by 2.1 MHz. (Since this black dotted line coincides with the green line in the figure and it is difficult to distinguish the two lines, it is shifted down for display). Third step, use a negative temperature coefficient resistor R ntc Perform temperature compensation on the FLL. The green line in the figure is the final effect. As the temperature changes from 0 °C to 70 °C, the frequency changes by 0.7 MHz. Compared with the solution without any compensation measures, the proposed solution makes the carrier frequency of the transmitter much more stable and can better adapt to temperature changes. Since the frequency value at each moment fluctuates around the target frequency of 433 MHz, for each test point in the figure, the simulation is 40 us, and then the frequency data from 20 us to 40 us is intercepted and averaged.

[0085] The low power consumption of the carrier generator is because: the reference circuit is processed first before introducing the FLL. Whether it is the frequency change introduced by the reference circuit or the CSVCO itself, it can be greatly reduced by the FLL. And as seen from Equation (5), after introducing the FLL, the reference circuit does not need to be very precise. However, performing the first step of using a positive temperature coefficient resistor Rptc to compensate the reference circuit is beneficial to reducing power consumption. The reasons are: (1) The influence of temperature on the frequency of the CSVCO will be weakened ( Figure 10 in the figure, from the red line to the blue line). The frequency range that can be adjusted by adding a capacitor is limited. To adjust a larger frequency range, a larger capacitor is required. After compensating the reference circuit, only a smaller-sized capacitor is needed to adjust. Figure 11 Shows the capacitance-voltage relationship of varactors of different sizes. In Figure 11 it can be seen that as the size of the varactor increases, although the change range of the capacitance becomes larger, no matter how it is adjusted, its capacitance value cannot be 0. The larger the size, the greater the residual capacitance. This means that when using a larger-sized varactor, to oscillate at the same frequency, a larger current is required, which will increase the power consumption. (2) After the temperature rises, the current change is not large, indicating that the power consumption will not increase significantly with temperature.

[0086] Alternative Embodiment

[0087] Figure 2 In this alternative embodiment, the transmitter of the foregoing embodiment of the present invention consists of four parts. The variant solution can remove the reference circuit and directly provide a stable bias current through an off-chip circuit. The other parts are the same as those of the present invention. Then, the problem of frequency variation with temperature is solved by two steps. First, an FLL is introduced to monitor and adjust the frequency of the CSVCO in real time; second, a resistor R with a negative temperature coefficient is used ntc to compensate the FLL and further increase the anti-temperature interference ability. Providing the reference current off-chip requires additional circuitry or power supply equipment, increasing the complexity of the sensor node. However, the bias current provided off-chip may have better temperature characteristics, completing the first step of the present invention, which is to compensate the reference circuit. Generally, the variant solution is similar to the principle of the present invention.

[0088] In the foregoing embodiment, the basic number of units of the SCPA is 3. The variant solution can design more basic units and introduce an SPI module to control these basic units. Finally, impedance matching is achieved by activating some of the units. Although this solution is more refined, it is similar to the principle of the foregoing embodiment.

[0089] The technical key points of this solution are mainly in three aspects: (1): Refer to Figure 3 In this figure, adjusting the current of the delay unit or the load capacitance at a certain node can change the frequency of the oscillator. Removing MP0 and MN0 in the figure and applying the control voltage Vc to the gate terminal of MN1 can adjust the current of the delay unit. However, when the circuit is powered on, Vc may be an uncertain value. Once Vc is too low, it is easy to cause the oscillator to fail to start, resulting in abnormal operation of the circuit. Therefore, the present invention improves the circuit and uses current biasing to change the frequency of the oscillator by adjusting the load capacitance. In Figure 4 it can be seen that the circuit can oscillate normally regardless of the value of Vc within 0 - 1.8V (i.e., the power supply voltage). (2): Three steps are taken to solve the problem of the carrier frequency of the transmitter varying with temperature. First, a resistor Rptc with a positive temperature coefficient is used to compensate the reference circuit; second, an FLL is introduced to monitor and adjust the frequency of the CSVCO in real time; third, a resistor R with a negative temperature coefficient is used ntcCompensate the FLL. In particular, performing the first step first can significantly reduce the power consumption of the carrier generator. (3): In a common PA, to solve the problem of excessive impedance transformation ratio in a low-power transmitter, a stacked PA architecture or reducing the power supply voltage is usually adopted. The present invention uses SCPA, which achieves the effect of reducing the power supply voltage without changing the power supply voltage. The switch-type PA has higher efficiency, and by activating some units, the optimal impedance close to the antenna impedance can be obtained, reducing the loss on the impedance matching network. At the same time, the output power can be adjusted to meet different requirements.

[0090] As described above, the present invention adopts three measures to solve the problem of the carrier frequency of the transmitter varying with temperature. The first step is to compensate the reference circuit; the second step is to introduce the FLL to monitor and adjust the frequency of the CSVCO in real time; the third step is to use a negative temperature coefficient resistor to compensate the FLL. In particular, performing the first step first can significantly reduce the power consumption of the carrier generator; in a common PA, to solve the problem of excessive impedance transformation ratio in a low-power transmitter, a stacked PA architecture or reducing the power supply voltage is usually adopted. The present invention uses SCPA, which achieves the effect of reducing the power supply voltage without changing the power supply voltage. The switch-type PA has higher efficiency, and by activating some units, the optimal impedance close to the antenna impedance can be obtained, reducing the loss on the impedance matching network. At the same time, the output power can be adjusted to meet different requirements.

[0091] In a wireless sensor network, power consumption and anti-temperature interference need to be compromised. The transmitter with anti-temperature interference of the carrier frequency has relatively high power consumption, and the temperature characteristics of the low-power transmitter are relatively poor. The present invention solves the problem of the carrier frequency being interfered by temperature at a relatively low power consumption through three measures. Using SCPA, a switch-type PA, to improve efficiency, and by activating some units, the loss on the impedance matching network is reduced. Finally, the transmitter proposed by the present invention has anti-temperature interference and lower power consumption. The feasibility of the present invention is verified by simulation software. The present invention effectively solves the two problems of excessive power consumption of the transmitter inside the sensor node and the carrier frequency being easily affected by temperature in the traditional wireless sensor network.

[0092] There have been some studies on low-power transmitters. To generate a stable carrier frequency, phase-locked loops are used in documents [2, 3, 4, 5], etc. The power consumption of the phase-locked loop is usually between several hundred microwatts and several milliwatts, and the power consumption is relatively high; to reduce the power consumption, documents [6, 7, 8], etc. directly use a low-power oscillator to generate the carrier signal, but do not solve the influence of temperature change on the carrier frequency. Manual adjustment is required after the temperature changes. And the influence of the reference circuit on the power consumption is ignored by the predecessors.

[0093] The remarkable advantages of the present invention are as follows: The transmitter is resistant to temperature interference and has lower power consumption. In the past, relatively complex modulation was adopted, which had high requirements for linearity, so a linear PA was selected. The linear PA is less efficient than the switching PA used in the present invention. There are also designs that use FLL to generate carrier signals. Since the frequency instability introduced by either the reference circuit or the CSVCO itself can be greatly improved by FLL. Moreover, as can be seen from Equation (5), the reference circuit does not need to be very precise. In terms of application scenarios, the present invention can be used not only in wireless sensor networks, but also in wireless communication systems such as the Internet of Things, wearable devices, and smart homes that require low power consumption but also accurate clocks.

[0094] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several alternatives or modifications can be made to these described embodiments, and these alternative or modified forms should be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description with reference to terms such as "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. Without conflict, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the protection scope of the patent application.

[0095] References:

[0096] 1. Otayf, N.; Abbas, M. In A Comparative Analysis of Energy Consumption in Wireless Sensor Networks, Pervasive Computing and Social Networking: Proceedings of ICPCSN 2021, 2022; Springer: 2022; pp 113 - 126.

[0097] 2. Babaie, M.; Kuo, F.-W.; Chen, H.-N.R.; Cho, L.-C.; Jou, C.-P.; Hsueh, F.-L.; Shahmohammadi, M.; Staszewski, R.B., A fully integrated Bluetooth low-energy transmitter in 28nm CMOS with 36% system efficiency at 3dBm. IEEE Journal of Solid-State Circuits 2016, 51, (7), 1547-1565.

[0098] 3. Yang, S.; Yin, J.; Yi, H.; Yu, W.-H.; Mak, P.-I.; Martins, R.P., A 0.2-V energy-harvesting BLE transmitter with a micropower manager achieving 25% system efficiency at 0-dBm output and 5.2-nW sleep power in 28-nm CMOS. IEEE Journal of Solid-State Circuits 2019, 54, (5), 1351-1362.

[0099] 4. Huang, H.; Liu, X.; Tang, Z.; Song, W.; Zhang, Y.; Ma, X.; Zhang, M.; Wang, J.; Wang, Z.; Li, G., A 2nJ / bit, 2.3% FSK error fully integrated sub-2.4GHz transmitter with duty-cycle controlled PA for medical band. IEEE Transactions on Circuits and Systems I: Regular Papers 2022, 69, (12), 5018-5029.

[0100] 5. Liu, Y.-H.; Bachmann, C.; Wang, X.; Zhang, Y.; Ba, A.; Busze, B.; Ding, M.; Harpe, P.; van Schaik, G.-J.; Selimis, G. In 13.2A 3.7mW-RX 4.4mW-TX fully integrated Bluetooth Low-Energy / IEEE 802.15.4 / proprietary SoC with an ADPLL-based fast frequency offset compensation in 40nm CMOS, 2015 IEEE international solid-state circuits conference-(ISSCC) digest of technical papers, 2015; IEEE: 2015; pp 1-3.

[0101] 6. Chiu, C.-Y.; Zhang, Z.-C.; Lin, T.-H., Design of a 0.6-V, 429-MHz FSK transceiver using Q-enhanced and direct power transfer techniques in 90-nm CMOS. IEEE Journal of Solid-State Circuits 2020, 55, (11), 3024-3035.

[0102] 7. Mercier, P.P.; Bandyopadhyay, S.; Lysaght, A.C.; Stankovic, K.M.; Chandrakasan, A.P., A sub-nW 2.4 GHz transmitter for low data-rate sensing applications. IEEE journal of solid-state circuits 2014, 49, (7), 1463-1474.

[0103] 8. Wang, H.; Wang, X.; Barfidokht, A.; Park, J.; Wang, J.; Mercier, P. P., A battery-powered wireless ion sensing system consuming 5.5 nW of average power. IEEE Journal of Solid-State Circuits 2018, 53, (7), 2043 - 2053.

[0104] 9. Winoto, R., Digital radio-frequency transmitters: An introduction and tutorial. IEEE Solid-State Circuits Magazine 2018, 10, (4), 70 - 80.

[0105] 10. Walling, J., Mixed-mode transceivers: A brief tutorial. IEEE Solid-State Circuits Magazine 2022, 14, (3), 53 - 64.

[0106] 11. Yoo, S.-M.; Walling, J. S.; Woo, E. C.; Jann, B.; Allstot, D. J., A switched-capacitor RF power amplifier. IEEE Journal of Solid-State Circuits 2011, 46, (12), 2977 - 2987.

[0107] 12. Lee, D.-G.; Salem, L. G.; Mercier, P. P., Narrowband transmitters: Ultralow-power design. IEEE Microwave Magazine 2015, 16, (3), 130 - 142.

[0108] 13. Choi, K.-S.; Ko, J.; Kim, K.-M.; Kim, J.; Lee, S.-G., A 0.3-to-1-GHz IoT transmitter employing pseudo-randomized phase switching modulator and single-supply class-G harmonic rejection PA. IEEE Journal of Solid-State Circuits 2021, 57, (3), 892-905.

[0109] 14. Choi, K.-S.; Kim, K.-M.; Ko, J.; Lee, S.-G., A 915 MHz IoT transmitter employing frequency tripler and digitally controlled duty-cycle / phase calibration. IEEE Journal of Solid-State Circuits 2022, 57, (11), 3336-3347.

[0110] 15. Huang, X.; Harpe, P.; Wang, X.; Dolmans, G.; de Groot, H. In A 0dBm 10Mbps 2.4 GHz ultra-low power ASK / OOK transmitter with digital pulse-shaping, 2010 IEEE Radio Frequency Integrated Circuits Symposium, 2010; IEEE: 2010; pp 263-266.

Claims

1. A low-power consumption temperature-interference-resistant transmitter for wireless sensor networks, characterized in that: include: A reference circuit, used for providing a reference current, wherein the reference circuit adopts a beta multiplier reference circuit BMR, including an off-chip resistor and an on-chip resistor with a positive temperature coefficient, so as to compensate for the influence of temperature and process changes on the current; Alternatively, without the reference circuit, a stable reference current is provided directly through an off-chip circuit; A carrier generator, comprising a current-starved voltage-controlled oscillator CSVCO and a frequency-locked loop FLL, wherein the CSVCO is used to generate an oscillation signal at low power consumption, and the FLL is used to monitor and adjust the frequency of the CSVCO in real time, and to use a resistor with a negative temperature coefficient for temperature compensation to enhance the carrier generator's ability to resist temperature interference; A buffer for isolating the carrier generator from the power amplifier and improving the drive capability of the carrier generator; The switched capacitor power amplifier SCPA is used to amplify signal power and realize OOK modulation by controlling the on and off of the SCPA, wherein the SCPA facilitates impedance matching with the antenna by activating some units to reduce the loss on the impedance matching network.

2. The transmitter according to claim 1, characterized in that The reference circuit also includes a resistor with a positive temperature coefficient for compensating for an increase in bias current caused by a temperature increase.

3. The transmitter according to claim 1 or 2, characterized in that The FLL comprises a frequency-to-voltage converter FVC for converting changes in the frequency of the CSVCO into corresponding changes in voltage.

4. The transmitter according to claim 3, characterized in that The FVC circuit utilizes the relationship between the equivalent switched capacitor resistance and the frequency, and utilizes the current flowing through the equivalent switched capacitor resistance to generate a frequency-dependent voltage.

5. The transmitter according to any one of claims 1 to 4, characterized in that: The carrier generator also includes an amplifier for adjusting the frequency of the oscillation signal generated by the CSVCO. The amplifier dynamically adjusts the control voltage Vc by comparing the reference voltage and the voltage generated by the FVC, thereby achieving stable control of the CSVCO frequency. The amplifier is part of the frequency locked loop FLL and is used to ensure the frequency stability of the oscillator.

6. The transmitter according to any one of claims 1 to 5, characterized in that: The buffer is composed of three stages of inverters, and is used to improve the driving capability of the carrier generator and isolate the carrier generator and the power amplifier SCPA; the buffer receives a signal from the carrier generator, enhances the driving capability of the signal through step-by-step inversion amplification, and isolates it to supply the power amplifier.

7. The transmitter according to any one of claims 1 to 6, characterized in that: The SCPA includes a plurality of basic power amplification units, and OOK modulation is realized by turning on and off a MOSFET control unit circuit, and the SCPA can activate some or all of the units according to output power requirements; preferably, the number of units is 3 or more.

8. The transmitter according to any one of claims 1 to 7, characterized in that: The transmitter operates at a frequency of 433 MHz and has an output power of approximately 0 dBm.

9. The transmitter according to any one of claims 1 to 8, characterized in that: The transmitter adopts OOK modulation, and by introducing a frequency locked loop FLL and a temperature compensation mechanism, the control voltage of CSVCO is dynamically adjusted by comparing the reference voltage with the voltage generated by the frequency-voltage converter FVC to achieve the stability of the carrier frequency.

10. The transmitter according to any one of claims 1 to 9, characterized in that: The transmitter also includes a matching network for impedance matching with the antenna, and an optimal impedance close to the antenna impedance is obtained by activating some SCPA units to further reduce the loss on the impedance matching network.

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