High-temperature non-silicon-based temperature measurement integrated circuit

Abstract

The application discloses a high-temperature non-silicon-based temperature measurement integrated circuit, which is realized based on the relationship between the threshold voltage of a metal oxide thin film transistor and the temperature of the metal oxide thin film transistor. The thin film transistor is used to charge a capacitor to a certain voltage by outputting a current under a certain source-drain voltage. Different threshold voltages corresponding to different temperatures correspond to different output currents, so as to correspond to different charging times. The temperature is measured by detecting the charging time of the capacitor. The circuit comprises a temperature sensing module, an ADC module and an automatic reset module. The temperature sensing module comprises a zinc oxide thin film transistor, a capacitor, a capacitor charging switch and a capacitor discharging switch. The ADC module comprises a multi-stage inverter cascade unit, a counter unit, a parallel-serial conversion unit and a Manchester coding unit. The highest measurement temperature range of the circuit can reach-50 DEG C-250 DEG C. The circuit has an automatic reset function and can independently and cyclically measure the temperature. The multi-stage inverter cascade shaping is adopted, so that the circuit is simplified and the power consumption is reduced.

Description

Technical Field

[0001] This invention belongs to the field of temperature sensing technology and relates to a high-temperature non-silicon-based temperature measurement integrated circuit, which is of great significance for temperature measurement in high-temperature conditions. Background Technology

[0002] Metal oxide thin-film transistors, such as zinc oxide thin-film transistors, have many obvious advantages. First, they have excellent high-temperature performance. Metal oxide thin-film transistors perform better than silicon transistors at high temperatures and can operate stably over a wider temperature range.

[0003] Secondly, it can operate at low voltages. Compared to silicon transistors, metal-oxide-slim thin-film transistors (MOSFETs) have lower operating voltages, which can reduce power consumption and improve battery life. Simultaneously, it has lower manufacturing costs; zinc oxide MOSFETs can be manufactured using lower-cost materials and processes compared to silicon transistors.

[0004] In addition, compared to silicon transistors, metal oxide thin-film transistors generate fewer pollutants during manufacturing and processing, making them more environmentally friendly.

[0005] Current digital temperature sensors are primarily manufactured using silicon-based chips, typically measuring temperatures from -55°C to 125°C, but unable to measure higher temperatures. Through extensive research and experimentation, we discovered that zinc oxide thin-film transistors exhibit minimal threshold voltage drift at 200°C during positive voltage temperature stress testing. Therefore, they can operate normally at 200°C and even higher temperatures. This invention designs a ZnO-TFT-based sensing circuit scheme to detect temperatures over a wider range. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-temperature non-silicon-based temperature measurement integrated circuit. This circuit uses metal oxide thin-film transistors such as zinc oxide to design the temperature measurement circuit, solving the problem that existing digital temperature sensors cannot measure high temperatures, and reducing power consumption and cost.

[0007] The technical solution adopted in this invention is:

[0008] A high-temperature non-silicon-based temperature measurement integrated circuit is disclosed. This circuit is based on the relationship between the temperature and the threshold voltage of a metal oxide thin film transistor. The metal oxide thin film transistor outputs current to charge a capacitor to a certain voltage at a certain source-drain voltage. Different temperatures correspond to different threshold voltages, which in turn correspond to different output currents and thus different charging times. The temperature is measured by detecting the capacitor charging time.

[0009] In the above technical solution, the circuit further includes a temperature sensing module, an ADC module, and an automatic reset module;

[0010] The temperature sensing module includes a metal oxide thin film transistor, a capacitor, a capacitor charging switch, and a capacitor discharging switch. The metal oxide thin film transistor is used to provide circuit input current, and the capacitor charging switch and capacitor discharging switch are switching MOS transistors used to control the charging and discharging of the capacitor.

[0011] The ADC module includes a multi-stage inverter cascade unit, a counter unit, a parallel-to-serial conversion unit, and a Manchester encoding unit;

[0012] When the capacitor charging switch is closed and the capacitor discharging switch is opened, the output current of the metal oxide thin film transistor charges the capacitor, the counter unit starts counting, and the output is saved to the parallel-to-serial conversion unit. When a certain voltage is reached, the cascaded multi-stage inverters output a high-level EN signal, which stops the counter module from counting. The parallel-to-serial conversion unit shifts the counter output result serially to the Manchester encoding unit for encoding. At the same time, the automatic reset module generates a reset signal, opens the capacitor charging switch, closes the capacitor discharging switch, discharges the capacitor, and resets all modules. After the discharge is complete, the capacitor charging switch is closed again, and the capacitor discharging switch is opened again to perform a second measurement.

[0013] Compared to other traditional silicon-based CMOS transistors, this invention uses metal oxide thin-film transistors, such as zinc oxide, to design the temperature measurement circuit. Multimode sensing circuits can also be used to measure various parameters, such as temperature, humidity, and pressure.

[0014] This invention employs a single-slope ADC, which improves accuracy and resolution. Furthermore, this ADC eliminates the need for a dedicated comparator circuit, simplifying the circuitry and reducing power consumption. An automatic reset circuit module is also included to automatically control the cyclic operation of the temperature measurement circuit.

[0015] According to a specific embodiment of the present invention, the metal oxide thin film transistor has a five-layer structure. The first layer is indium tin oxide (ITO) as the source and drain material, the second layer is zinc oxide (ZnO), IGZO, IZO, or a mixed oxide material of indium, tin, and zinc as the channel, the third and fourth layers are aluminum oxide (Al2O3) as the insulating layer, and the fifth layer is indium tin oxide (ITO) as the gate material; the substrate is selected as needed.

[0016] According to a specific embodiment of the present invention, the metal oxide thin-film transistor is a zinc oxide thin-film transistor; the circuit includes:

[0017] Temperature sensing circuit: Since temperature has a certain linear relationship with the threshold voltage of the ZnO-TFT, and the current of the NMOS transistor also has a certain relationship with the threshold voltage, different threshold voltages correspond to different currents at a given voltage. Different currents result in different charging times for the capacitor. Therefore, temperature can be measured by measuring the capacitor charging time. Furthermore, multi-mode sensing can be used, with a four-channel NMOS switch controlling the parameters to be measured.

[0018] ADC Module: Employing a single-slope ADC simplifies the circuit structure, reduces cost, and maintains basic accuracy. Since the capacitor charging voltage reaches approximately 3.1V at various temperatures (the charging voltage can be adjusted by changing the threshold voltage based on capacitor size, counter range, and charging speed requirements), the subsequent multi-stage inverters output a high-level flip-flop voltage. This inverter flip-flop voltage is used as the comparator output signal to control the operation of other units in the ADC module, eliminating the need for a dedicated comparator circuit and simplifying the design.

[0019] Other units in this module include a counter unit, a parallel-to-serial converter unit, and a Manchester encoding circuit. The counter uses a nine-bit asynchronous counter, and a low-level enable is achieved by stopping the clock through an NOR gate. The parallel-to-serial converter unit is connected to the counter unit and uses a control signal to write at a low level and shift at a high level, outputting a nine-bit serial digital code. The Manchester encoding circuit is connected to the output of the parallel-to-serial converter unit and encodes the output nine-bit serial code into an 18-bit digital code.

[0020] Automatic reset circuit: This circuit achieves cyclic temperature measurement through logic design controlling the output and capacitor charging / discharging. According to a specific embodiment of the invention, the temperature sensing module, i.e., the zinc oxide TFT, outputs current to charge the capacitor, and the counter module starts counting. Simultaneously, the parallel-to-serial conversion module saves the counting result. When the voltage reaches approximately 3.1V, a high-level EN signal is output through ten inverters. This signal stops the counter module from counting, shifts the saved result from the parallel-to-serial conversion module, and outputs it via a Manchester encoding module. When a valid signal is output, the reset circuit module generates a reset signal to discharge the capacitor and reset all modules. After the discharge is complete, a second measurement is performed.

[0021] The beneficial effects of this invention are:

[0022] Completely different from traditional CMOS circuits, the transistors used in this invention are thin-film transistors, using materials such as zinc oxide (ZnO), IGZO, IZO, or mixed oxides of indium, tin, and zinc as the channel, indium tin oxide (ITO) as the gate material and electrical signal transmission medium, and aluminum oxide (Al2O3) as the insulating layer. The substrate is no longer limited to large-area silicon, but can be freely selected, such as inexpensive materials (which can significantly reduce costs), transparent materials (which can inherit the transparent properties of the substrate), and flexible materials (which can inherit the excellent ductility of the substrate), which greatly reduces costs.

[0023] The entire circuit was designed and laid out using ZnO thin-film transistor devices, including a temperature sensing module, an ADC module, and an automatic reset circuit module. The simulation test was successful. A single-slope ADC without comparators was achieved by using multi-stage inverter cascade shaping, which simplifies the circuit, reduces power consumption, and the maximum measurement temperature range can reach -50℃ to 250℃.

[0024] An automatic circuit reset function was designed, which can autonomously and cyclically measure temperature.

[0025] By employing the concepts of signal multiplexing and counter multiplexing, power consumption and area are greatly reduced.

[0026] In addition, multi-mode sensing channels can be used, and the required analog values ​​to be measured, such as temperature and pressure, can be selected according to the decoder. Attached Figure Description

[0027] Figure 1 This is a diagram of the top gate structure of a ZnO-TFT.

[0028] Figure 2 Io of ZnO-TFT NMOS at 50℃–250℃ D -V G Transfer characteristic diagram.

[0029] Figure 3 I for 200℃ ZnO-TFT NMOS D -V G Transfer characteristic diagram.

[0030] Figure 4 This is a block diagram of the overall temperature measurement circuit.

[0031] Figure 5 It is a traditional three-tube temperature sensing circuit.

[0032] Figure 6 This is a schematic diagram of a temperature sensing circuit.

[0033] Figure 7 The threshold voltage-temperature relationship of ZnO-TFT is shown in the figure.

[0034] Figure 8 The capacitor charging curves are shown at different temperatures.

[0035] Figure 9 This is a schematic diagram of a parallel-to-serial converter circuit.

[0036] Figure 10 This is a circuit diagram for the Manchester encoding.

[0037] Figure 11 This is the schematic diagram of an automatic reset circuit.

[0038] Figure 12 This is a simulation diagram of an automatic reset circuit.

[0039] Figure 13 This is the schematic diagram of the overall multimode sensing circuit.

[0040] Figure 14 Output simulation diagram for 50℃.

[0041] Figure 15 Output simulation image at 125℃.

[0042] Figure 16 Output simulation diagram for 200℃.

[0043] Figure 17 For circuit layout design.

[0044] Figure 18 This is the output result of the post-simulation. Detailed Implementation

[0045] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] In this invention, the entire circuit chip uses metal oxide thin-film transistors (MOTS) such as zinc oxide thin-film transistors (ZnO-TFTs) instead of traditional CMOS transistors. Taking ZnO-TFTs as an example, ZnO-TFT devices are deposited layer by layer on a substrate using thin-film deposition technology, and specific patterns are obtained through photolithography and etching. ZnO-TFT devices mainly have bottom-gate and top-gate structures. The ZnO-TFTs used in the embodiments of this invention adopt a top-gate structure, such as... Figure 1As shown, placing the gate on the top layer allows the top-gate structure to better protect the active semiconductor layer compared to the bottom-gate structure. The first layer is the source / drain electrode layer, which can be made of ITO or Cr / Au depending on the requirements. The second layer is the channel active region, where a 20nm layer of ZnO material is deposited on top of the source / drain layer via ALD, and a 10nm layer of Al2O3 is also deposited on top to prevent direct contact between ZnO and water, acids, or alkalis. The third layer is a 20nm Al2O3 insulating layer. The fourth layer is the gate electrode layer, which can be made of ITO or Cr / Au depending on the requirements, and its thickness is determined by the process specifications. The channel layer can also use IGZO, IZO, or a mixed oxide material of indium, tin, and zinc to form other metal-oxide thin-film transistors.

[0047] Through extensive experimentation and adjustment of process parameters, this invention ultimately yielded excellent ZnO TFT characteristics. Figure 2 The figure shows V at temperatures ranging from 50℃ to 250℃. DS At 5V, the ZnO-TFT NMOS device maintains good transfer characteristics. Figure 3 The image shows the I of a 200℃ ZnO-TFT NMOS. D -V G The curve shows that the threshold voltage drift of the device is small at 200℃, so the device has excellent high temperature resistance and is suitable for a wide range of detection temperatures.

[0048] Overall block diagram:

[0049] This invention uses a zinc oxide thin-film transistor as the main design element and designs a complete temperature measurement circuit with automatic reset function. Its overall structural block diagram is shown below. Figure 4 As shown, it includes a temperature sensing circuit, an ADC module circuit, and a reset module circuit.

[0050] Iout is the output current generated by the temperature sensing circuit. This current charges capacitor Cp, at which point switch A is closed. When turned on, the ADC module starts working, and the counter starts counting. When the voltage across the capacitor reaches a certain value, it outputs a high level EN to stop the counter. The output obtained by the digital circuit is processed and encoded by subsequent circuits to obtain a serial output digital code.

[0051] After the output is complete, the reset circuit module generates a reset signal Rst to open switch A. The circuit closes and clears the values ​​of all registers. Simultaneously, the capacitor discharges. After a certain discharge time, this module generates a Restart signal, causing the reset circuit module to stop working and closing switch A, thus opening... The capacitor begins to recharge, and the temperature measuring circuit prepares for the next temperature measurement.

[0052] Circuit principle scheme:

[0053] 1. Temperature sensing circuit

[0054] 1.1 Temperature detection using threshold voltage

[0055] Traditional three-tube temperature sensor circuit structure, such as Figure 5 As shown, temperature can be detected by obtaining a current that is linearly related to temperature, based on the relationship between the threshold voltage Vth and the gain factor β and temperature. From... Figure 5 It can be observed that M4, M5, M6, and M7 form a cascade current mirror, the currents of M2 and M3 are equal to the current of M1, and the currents of M8 and M9 follow the currents of M3 and M2, respectively.

[0056] It can be obtained.

[0057] As can be seen from the formula, the current has a very small rate of change. The circuit structure is simple and the performance is stable. Due to the use of the cascade current mirror, the power supply rejection of the output voltage is relatively low.

[0058] However, the change in current with temperature is not completely linear, so a more precise calibration circuit is required, which greatly increases the power consumption of the overall circuit.

[0059] 1.2 Temperature Sensing Circuit

[0060] After trying, Figure 5 The temperature sensing circuit shown, even after optimization, is still unsuitable for the design scheme of this invention, as its output current is inconvenient to connect to subsequent circuits. The embodiment of this invention is designed as follows: Figure 6 The temperature sensing circuit shown uses enhancement-mode NMOS transistors. One NMOS transistor provides the circuit input current, while the second and third NMOS transistors are switching MOS transistors that control the charging and discharging of the capacitor, and also function as a reset circuit.

[0061] By measuring the time of high-level signal generation as the capacitor charging time, and since the capacitor charging time is linear with the counter count, if the relationship between temperature and capacitor charging time is obtained, the temperature can be directly measured through the counting results.

[0062] Extensive experimental testing has revealed a certain relationship between temperature and the threshold voltage of ZnO-TFTs, such as... Figure 7As shown, this is a curve with good linearity, making it relatively easy to fit the relationship between temperature and analog output. Furthermore, different ambient temperatures can be simulated by changing the threshold voltage, facilitating simulation testing. Besides obtaining the relationship between the threshold voltage and temperature, the current of the NMOS transistor is also related to Vth. Under a given voltage, different threshold voltages correspond to different currents, and different currents result in different charging times for the capacitor. Therefore, the temperature can be measured by measuring the capacitor charging time.

[0063] Figure 8 The figure shows the capacitor charging curve and the EN signal output curve at temperatures ranging from 50℃ to 200℃. The lower the temperature, the higher the threshold voltage, the lower the current, and the longer the charging time. Placing these curves on the same simulation graph makes it easier to observe the changes. It can be seen that when the voltage across the capacitor reaches approximately 3.1V, the multi-stage inverter will output a high-level signal.

[0064] 2. ADC module

[0065] This invention provides an ADC circuit that does not require a comparator, comprising a counter, a parallel-to-serial converter, and Manchester encoding.

[0066] ①Since the flip-over voltage threshold of the ZnO-TFT device is basically the same at different temperatures, a comparator can be directly implemented by connecting an inverter after the capacitor. Simulation tests showed that when the voltage across the capacitor reaches about 3.1V, a high level is generated through the dual inverters. This high-level signal determines the operation of the subsequent digital part, and this characteristic perfectly plays the role of the comparator in the ADC circuit. Figure 6 The capacitor charging voltage shown is followed by ten inverters instead of two inverters. The purpose of this is to shape the inverter output to make it closer to the ideal inverter output so that it can output a high level in the shortest possible time.

[0067] ② The counter module (i.e., the capacitor charging counter) uses a nine-bit asynchronous counting method and has a low-level reset terminal and a low-level enable terminal. The enable principle is to use a NOR gate, with the input terminal connected to the clock and EN. When EN is high, the clock input terminal of the counter is reset to zero, thus stopping the counter from counting; when EN is low, the clock is input normally, and the counter works normally. That is, the counter counts when the capacitor is charging and stops counting when the high-level enable arrives.

[0068] ③ Figure 9 The diagram shows a specific circuit structure of the parallel-to-serial conversion circuit in the ADC module. The circuit function is controlled by the W&S control signal. When the signal is low, the shift register stores each bit of the output value in the counter. When the signal is high, the output of each register is the output of the previous register. That is, the shift register will shift right bit by bit to output a nine-bit serial code.

[0069] The design logic is as follows:

[0070]

[0071] Therefore, we can use the EN signal generated by capacitor charging as this control signal. When the capacitor is charging, EN is low, the counter counts normally, and the output is stored in this module. When EN is high, the counter stops counting and maintains the output, while this circuit module will shift the counter output result serially.

[0072] ④ This invention employs a Manchester encoding circuit with dual clock inputs, such as... Figure 10 As shown.

[0073] This circuit design requires only one global clock input, where clk / 2 is a divide-by-two clock value. A high input results in a low output during the first half of the clock cycle and a high output during the second half; a low input results in a high output during the first half of the clock cycle and a low output during the second half.

[0074] Its output logic is as follows

[0075] The enable terminal EN in this circuit is the high-level output after the capacitor is charged. It uses the serial output generated by the ADC module as the input encoding and output, and then passes it to the subsequent microcontroller for processing.

[0076] This module firstly ensures good signal synchronization. Since the state of each bit is represented by two voltage levels, the receiver can determine the state of each bit by detecting changes in these levels, thus guaranteeing signal synchronization. Secondly, it provides high interference immunity. Each bit in the Manchester encoder contains two voltage level changes, so even with noise interference, the bit state can be determined by detecting these two voltage level changes, thereby improving the signal's interference immunity. Furthermore, when there are many consecutive high voltage levels in the data, continuous operation of the load may increase the power consumption of the entire circuit, leading to insufficient chip power. Therefore, the Manchester encoder is very useful for low-power passive chips.

[0077] 3. Automatic reset circuit

[0078] This invention employs an automatic reset mechanism, utilizing a counter multiplexing method to achieve the functions of clearing the control register and restarting the circuit. A four-bit counter (reset counter) controls the number of output bits and the generation of the reset signal. When the Manchester encoding circuit outputs an 18-bit digital code, this counter outputs a reset signal to clear the capacitor charging counter, shift register, Manchester encoder, etc., while simultaneously opening the capacitor charging switch and closing the capacitor discharging switch.

[0079] The output Release signal indicates that the capacitor has started discharging. To ensure that the capacitor is fully discharged, a seven-bit counter (counter_6) is used to control the discharge time, which basically ensures that the capacitor is fully discharged. When the discharge is finished, a Restart signal will be output to clear the reset counter (counter_4), the reset signal will be invalidated, the capacitor discharge switch will be opened and the capacitor charging switch will be closed, thereby resetting the initial state of the circuit and the capacitor will start charging again.

[0080] The logical expression for the reset circuit control signal is:

[0081] Restart=discharge·EN+Rst·discharge·EN!

[0082] The discharge signal is the output signal of counter_7, indicating that the capacitor has finished discharging. Figure 11 This is a specific implementation circuit example of the present invention, wherein the reset circuit is implemented based on the above-described approach, specifically as follows: Figure 11 As shown within the middle frame.

[0083] Figure 12 The image shows the serial digital code output cyclically at 200℃. The reset circuit is working normally and can realize automatic reset circuit.

[0084] 4. Overall Circuit

[0085] Figure 13 The circuit shown is the overall temperature measurement circuit. A multi-mode sensing channel is added to the front-end analog circuit. By selecting the decoder, four different analog quantities can be measured. Figure 14 The serial digital code output at 50℃ has a charging time of 933.1ms. The counting clock period used is 2ms. The theoretical count is 466, and the actual count is 465. Figure 15 The output serial digital code is shown at 125℃. The charging time is 324ms, the theoretical count is 162, and the actual count is 161. Figure 16 The output serial digital code is shown at 200℃. The charging time is 147.3ms, the counting clock cycle is theoretically 73, and the actual count is 72.

[0086] 5. Layout Design

[0087] like Figure 17 The diagram shows the layout design of the temperature measurement circuit. The left side is the ground line and the right side is the power line. Some modules use a shared power line to reduce the layout area. A PAD is added for probe testing to measure the output of important signals. Figure 18The results shown are post-simulation results after extracting layout parameters at 200℃. The theoretical count is 13, and the actual count is 12, which meets the design requirements.

Claims

1. A high-temperature non-silicon-based temperature measurement integrated circuit, characterized in that, This circuit is based on the relationship between the temperature and the threshold voltage of a metal oxide thin film transistor (MTBT). Under a certain source-drain voltage, the output current of the MTBT charges the capacitor to a certain voltage. Different temperatures correspond to different threshold voltages, which in turn correspond to different output currents and thus different charging times. The temperature is measured by detecting the capacitor charging time. The integrated circuit includes a temperature sensing module, an ADC module, and an automatic reset module. The temperature sensing module includes a metal oxide thin film transistor, a capacitor, a capacitor charging switch, and a capacitor discharging switch. The metal oxide thin film transistor is used to provide circuit input current, and the capacitor charging switch and capacitor discharging switch are switching MOS transistors used to control the charging and discharging of the capacitor. The ADC module includes a multi-stage inverter cascade unit, a counter unit, a parallel-to-serial conversion unit, and a Manchester encoding unit; When the capacitor charging switch is closed and the capacitor discharging switch is opened, the output current of the metal oxide thin film transistor charges the capacitor, the counter unit starts counting, and the output is saved to the parallel-to-serial conversion unit. When a certain voltage is reached, the cascaded multi-stage inverters output a high-level EN signal, which stops the counter module from counting. The parallel-to-serial conversion unit shifts the counter output result serially to the Manchester encoding unit for encoding. At the same time, the automatic reset module generates a reset signal, opens the capacitor charging switch, closes the capacitor discharging switch, discharges the capacitor, and resets all modules. After the discharge is complete, the capacitor charging switch is closed again, and the capacitor discharging switch is opened again to perform a second measurement.

2. The high-temperature non-silicon-based temperature sensing integrated circuit according to claim 1, characterized in that, The metal oxide thin-film transistor uses indium tin oxide (ITO) or Cr / Au as the source and drain materials, zinc oxide (ZnO), IGZO, IZO, or a mixed oxide material of indium, tin, and zinc as the channel, aluminum oxide (Al2O3) as the insulating layer, and indium tin oxide (ITO) or Cr / Au as the gate material; it adopts a bottom gate or top gate structure.

3. The high-temperature non-silicon-based temperature sensing integrated circuit according to claim 1, characterized in that, The multi-stage inverter cascade unit uses ten inverters connected in series to shape the inverter output, and outputs a high level in the shortest possible time.

4. The high-temperature non-silicon-based temperature sensing integrated circuit according to claim 1, characterized in that, The counter unit adopts a nine-bit asynchronous counting method and has a low-level reset terminal and a low-level enable terminal. The enable principle is to use a NOR gate, with the input terminal connected to the clock and EN. When EN is high, the clock input terminal of the counter is set to zero, thereby stopping the counter from counting. When EN is low, the clock is input normally, and the counter works normally. That is, the counter counts when the capacitor is charging and stops counting when the high-level enable arrives.

5. The high-temperature non-silicon-based temperature sensing integrated circuit according to claim 1, characterized in that, The automatic reset module is based on the concept of counter multiplexing. It uses a reset counter to control the number of output bits and the generation of the reset signal. When the Manchester encoding unit outputs an 18-bit digital code, this counter outputs a reset signal to clear the capacitor charging counter and all other modules. At the same time, it disconnects the capacitor charging switch and closes the capacitor discharging switch. To ensure the capacitor is fully discharged, a seven-bit counter is used to control the discharge time. When the discharge is complete, it outputs a Restart signal to clear the reset counter. If the reset signal fails, the capacitor discharge switch is opened and the capacitor charging switch is closed, thereby resetting the circuit's initial state and allowing the capacitor to start charging again.

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