A bootstrap switch structure that does not affect device life
By designing a bootstrap switch structure in an analog-to-digital converter, using a bootstrap circuit composed of switching modules and capacitors and a substrate gate circuit with two-phase non-overlapping clock control, the traditional bootstrap switch introduces nonlinearity and Lifespan problem achieves the effect of signal linearity and lifespan extension.
Patent Information
- Application Number
- CN202010806149.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2020-08-12
- Publication Date
- 2024-12-17
- Estimated Expiration
- 2040-08-12
AI Technical Summary
Traditional bootstrap switches introduce nonlinearity in analog-to-digital converters, resulting in switch tube life problems, and the dynamic performance of CMOS switches deteriorates when inputting broadband signals, making it difficult to maintain signal linearity.
A bootstrap switch structure is designed, and the bootstrap voltage generation circuit is formed by 4 switching modules and capacitor C1. Combined with a substrate gate circuit and two-phase non-overlapping clock control, it ensures that the voltage difference between the switch tube is not Exceeding the supply voltage, reducing on-resistance changes and leakage.
It achieves the extension of the life of the atmospheric switch tube while ensuring signal linearity, reduces the impact of nonlinear errors and leakage, and improves the performance of the analog-to-digital converter.
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Figure CN111970004B_ABST
Abstract
Description
Technical Field
[0001] The invention is a special switch circuit, which plays a vital role in an analog-to-digital converter and belongs to the field of analog circuit design. Background Art
[0002] Analog to digital converter (ADC) is an indispensable component in digital-to-analog conversion systems. It is widely used in broadcasting stations, radars, submarine equipment, audio processing, video processing, wireless communications, data collection, medical imaging, digital equipment, industrial automation and other application scenarios.
[0003] There is a sample-and-hold circuit at the front end of the analog-to-digital converter, which can be equivalent to a switched capacitor structure. Its function is to sample the input signal, discretely process the input analog signal in the time domain, and ensure that the processed discrete signal is continuous in amplitude. The larger the input bandwidth of the analog-to-digital converter, the higher the requirement for introducing nonlinearity to this switch. Traditional bootstrap switches (such as Figure 1 As shown in the figure, the nonlinearity introduced during sampling can be reduced. However, the gate voltage of the switch tube is the power supply + Vin, which makes its gate-to-substrate voltage greater than the power supply voltage, causing device life problems. If the structure of the bootstrap switch is not changed, the methods that can be used and their disadvantages are as follows: 1. The switch tube uses a high-voltage device. The disadvantage is that the high-voltage device is not well conducted in the low-voltage domain, introducing additional nonlinear errors. 2. The switch tube uses a deep N-well device and connects its substrate to the source end. The disadvantage is that it will cause leakage after the sampling is completed, introducing a larger error.
[0004] The bootstrap switch structure involved in the present invention can be applied to an analog-to-digital converter, which ensures the linearity of the switch output signal while not affecting the life of the switch tube. Summary of the invention
[0005] (1) Purpose of the Invention
[0006] Since the resistance of the CMOS switch changes with the input signal, when the CMOS switch is used in the front end of the analog-to-digital converter for broadband signal input, its dynamic performance will decrease as the input signal frequency increases, that is, the CMOS switch introduces nonlinearity that is positively correlated with the input signal frequency. The use of traditional bootstrap switches can reduce switch nonlinearity, but it will introduce life issues for normal voltage devices. Therefore, based on the above application environment analysis, I have invented a bootstrap switch structure with a simple structure that ensures the linearity of the switch input signal while not affecting the life of the low-voltage device.
[0007] (2) Technical solution
[0008] like Figure 2As shown, the bootstrap voltage generating circuit is composed of four switch modules S1, S2, S3, S4 and a capacitor C1, wherein one end of S1 and S3 is connected to the upper plate of the capacitor C1, one end of S2 and S4 is connected to the lower plate of the capacitor C1, the other end of S1 is connected to the power supply, the other end of S2 is grounded, the other end of S3 is connected to the gate of the switch tube, and the other end of S4 is connected to the input signal port (Vin);
[0009] The switch tube with substrate gating circuit is composed of a switch tube Ndnw, a switch module S5 and a substrate gating circuit, wherein: the switch tube Ndnw adopts a deep N-well NMOS tube, whose source and drain terminals are respectively connected to the sampling input signal terminal (Vin) and the switch output terminal (Vout), and its gate is connected to one end of S3 and S5, and the other end of S5 is grounded, which is used to control the switch tube to be cut off; the substrate gating circuit is composed of two switch modules S6 and S7, one end of S6 and S7 is connected to the switch tube substrate, the other end of S6 is grounded, and the other end of S7 is connected to the input signal port (Vin).
[0010] The bootstrap switch is controlled by a two-phase non-overlapping clock, where their effective phases are defined as Φ1 and Φ2. Its working principle is as follows:
[0011] Φ1 is effective: Figure 3 As shown, this stage is the holding phase, switches S1 and S2 are turned on, switches S3 and S4 are turned off, and the voltage difference across capacitor C1 is charged to the power supply voltage; switch S5 is turned on, the gate of Ndnw is grounded, and the switch is turned off; switch S6 is turned on, and switch S7 is turned off. At this time, the substrate of switch tube Ndnw is grounded to prevent the substrate from leaking to the Vin end;
[0012] Φ2 is effective: Figure 4 As shown, this stage is the sampling phase, switches S1, S2, and S5 are turned off, and switches S3 and S4 are turned on. From the law of conservation of charge, it can be seen that the voltage difference across C1 is the power supply voltage, that is, the gate-source voltage of the switch tube Ndnw is the power supply voltage and remains unchanged; switch S7 is turned on, switch S6 is turned off, and the source-substrate voltage of the switch tube is at the same level, so: 1. The voltage difference between any two ends of the switch tube does not exceed the power supply, and will not affect the life of the switch tube; 2. The threshold voltage of the switch tube is constant, and the on-resistance change is further reduced. BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Figure 1 Conventional Bootstrap Switching Structure
[0014] Figure 2 The present invention bootstrap switch structure
[0015] Figure 3 , the bootstrap switch maintains the phase working state
[0016] Figure 4 , the sampling phase working state of the bootstrap switch DETAILED DESCRIPTION
[0017] First, put Figure 1 It is a traditional bootstrap switch structure, which is changed to Figure 2 structure, and then Figure 2 The ideal switches S1, S2, S3, S4, S5, S6 and S7 in the above diagram are replaced by actual MOS switches. The size of switches S1 to S7 and the selection of switch tube types should ensure that the switches can be turned on normally and the leakage current when turned off should be as small as possible, because one end of capacitor C1 is suspended in the sampling phase, and the leakage current will affect the sampling. Finally, two-phase non-overlapping clocks are introduced to control switches S1 to S7 respectively, so that their working states are respectively Figure 3 and Figure 4 The holding phase and sampling phase are shown.
[0018] Note that a certain compromise must also be considered in the selection of the capacitor C1 value: if C1 is too small, due to the existence of the gate parasitic capacitance of the switch tube Ndnw, the gate-source voltage of the switch tube is far from the power supply voltage, which will cause poor switch conduction; when C1 is too large, the switch startup time becomes longer; you can choose C1 equal to 10 times the gate parasitic capacitance of the switch tube.
[0019] In summary, the present invention realizes the improvement of the traditional bootstrap switch through the above technical scheme, so that the voltage difference between any two ports of the switch tube in the traditional bootstrap switch does not exceed the power supply voltage, thereby increasing the life of the normal voltage switch tube. At the same time, the circuit structure is simple, portable and practical.
Claims
1. A bootstrap switch structure that does not affect the life of the device, characterized in that: The bootstrap switch consists of a switch tube with a substrate gating circuit and a bootstrap voltage generating circuit, wherein: The bootstrap voltage generating circuit is composed of four switch modules S1, S2, S3, S4 and capacitor C1, wherein one end of S1 and S3 is connected to the upper plate of capacitor C1, one end of S2 and S4 is connected to the lower plate of capacitor C1, the other end of S1 is connected to the power supply, the other end of S2 is grounded, the other end of S3 is connected to the gate of the switch tube, and the other end of S4 is connected to the input signal port Vin; The switch tube with substrate gating circuit is composed of a switch tube Ndnw, a switch module S5 and a substrate gating circuit, wherein: the switch tube Ndnw adopts a deep N-well NMOS tube, whose source and drain terminals are respectively connected to a sampling input signal terminal Vin and a switch output terminal Vout, and whose gate is connected to one end of S3 and S5, and the other end of S5 is grounded, so as to control the switch tube to be cut off; the substrate gating circuit is composed of two switch modules S6 and S7, one end of S6 and S7 is connected to the substrate of the switch tube Ndnw, the other end of S6 is grounded, and the other end of S7 is connected to the input signal port Vin; the switch tube Ndnw is a deep N-well NMOS tube with a switch logic on the substrate, in the sampling phase, the switch S7 is turned on, the switch S6 is turned off, and the source-substrate voltage of the switch tube Ndnw is at the same level, in the holding phase, the switch S6 is turned on, the switch S7 is turned off, and the substrate of the switch tube Ndnw is grounded at this time.