CN108563277B - Exponential waveform current generation circuit based on CMOS - Google Patents
Exponential waveform current generation circuit based on CMOS Download PDFInfo
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- CN108563277B CN108563277B CN201810597747.8A CN201810597747A CN108563277B CN 108563277 B CN108563277 B CN 108563277B CN 201810597747 A CN201810597747 A CN 201810597747A CN 108563277 B CN108563277 B CN 108563277B
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
- G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
- G05F1/10—Regulating voltage or current
- G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
- G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices
Abstract
The invention discloses an exponential waveform current generating circuit based on a CMOS (complementary metal oxide semiconductor). A specific voltage is applied to the grid electrodes of a group of PMOS (P-type metal oxide semiconductor) or NMOS (N-type metal oxide semiconductor) transistors, so that the transistors work in a saturation region, and the sum of the output currents of the drain electrodes of the group of transistors presents a waveform which is approximately exponentially changed along with time. Compared with the traditional exponential waveform current generation circuit based on a single transistor working in a subthreshold state, the exponential waveform current generation circuit obtained by the method has stronger driving capability and generates more accurate exponential waveform output current. The time constant of the exponential waveform may be determined by the capacitance in the circuit, the gate preset voltage, the magnitude of the current source connected to the gate, and the transistor threshold voltage. The exponential waveform current generation circuit has the advantages of low cost, high precision and strong driving capability.
Description
Technical Field
The invention belongs to the technical field of integrated circuits, and particularly relates to an exponential waveform current generation circuit based on a CMOS (complementary metal oxide semiconductor).
Background
The exponential waveform current generation circuit based on the CMOS has wide application, and can be mainly applied to a neurostimulator chip. The traditional exponential waveform current generation circuit is generally realized based on a single transistor working in a subthreshold region and has smaller output driving capability.
The patent discloses a based on taylor's approximate principle, through the specific voltage of grid to two transistors, make the drain current sum combination of transistor produce the circuit that presents exponential waveform output current with time, its structure is exquisite, and the output capacity is strong, and the exponential waveform current error who obtains is little. Compared with the traditional exponential waveform current generation circuit, the circuit realized by the method has more advantages in the aspects of precision and driving performance because the transistors work in a saturation region.
Disclosure of Invention
The technical problem to be solved by the invention is to provide an exponential waveform current generating circuit based on a CMOS, which has the characteristics of low cost, high precision and strong driving capability.
In order to achieve the purpose, the invention adopts the following technical scheme
An exponential waveform current generation circuit based on a CMOS comprises a constant current source (100), a pre-charging capacitor (101), a second output transistor (102), a first output transistor (103) and a preset voltage circuit (105), wherein the output end of the preset voltage circuit (105) is respectively connected with an upper plate of the pre-charging capacitor (101) and an upper plate of an MOS transistor capacitor (104); wherein the content of the first and second substances,
the drain electrode of the first output transistor (103) is connected with the drain electrode of the second output transistor (102), the drain electrodes of the first output transistor (103) and the second output transistor (102) are combined to generate total output current, the grid electrode of the first output transistor (103) is connected with the upper plate electrode of an MOS transistor capacitor (104), namely the grid electrode of the MOS transistor capacitor (104), and the lower plate electrode of the MOS transistor capacitor (104), namely the drain electrode, the source electrode and the substrate of the MOS transistor capacitor (104) are all grounded; the source of the first output transistor (103) is grounded;
the grid electrode of the second output transistor (102), the upper plate of the pre-charging capacitor (101) and the cathode of the constant current source (100) are connected; the source of the second output transistor (102), the lower plate of the pre-charging capacitor (101) and the anode of the constant current source (100) are grounded.
Preferably, the method comprises the following steps: the sum of the drain currents of the second output transistor (102) and the first output transistor (103) may be approximated to a total current exhibiting an exponential waveform change with time within a preset time range.
Preferably, the method comprises the following steps: and determining the time constant of the exponential waveform according to the sizes of the constant current source (100) and the pre-charging capacitor (101).
Advantageous effects
The taylor approximate current pulse generating circuit of the present invention improves the output accuracy for a neurostimulator for biomedical use. The square relationship of the applied saturation region current to the over-saturated voltage contained in the taylor-like current pulse generating circuit is relatively accurate in implementation. Meanwhile, the saturation region range of the MOS tube is large, and the current output in a large range can be ensured only by well controlling the preset control voltage.
Drawings
Fig. 1 is an overall circuit diagram of an exponential current pulse to obtain a taylor approximation: for generating an output pulse to be applied to a load;
wherein: 100 is a constant current source; 101 is a pre-charge capacitor; 102 is a second output crystal
A body duct; 103 is a first output transistor; 104 is an equivalent capacitance voltage control transistor;
105 is a preset voltage circuit module;
Detailed Description
As shown in fig. 1, the present invention provides an exponential waveform current generating circuit based on CMOS, which includes a constant current source (100), a pre-charge capacitor (101), a second output transistor (102), a first output transistor (103), and a preset voltage circuit (105), wherein an output terminal of the preset voltage circuit (105) is respectively connected to an upper plate of the pre-charge capacitor (101) and an upper plate of a MOS transistor capacitor (104); wherein the content of the first and second substances,
the drain electrode of the first output transistor (103) is connected with the drain electrode of the second output transistor (102), the drain electrodes of the first output transistor (103) and the second output transistor (102) are combined to generate total output current, the grid electrode of the first output transistor (103) is connected with the upper plate electrode of an MOS transistor capacitor (104), namely the grid electrode of the MOS transistor capacitor (104), and the lower plate electrode of the MOS transistor capacitor (104), namely the drain electrode, the source electrode and the substrate of the MOS transistor capacitor (104) are all grounded; the source of the first output transistor (103) is grounded;
the grid electrode of the second output transistor (102), the upper plate of the pre-charging capacitor (101) and the cathode of the constant current source (100) are connected; the source of the second output transistor (102), the lower plate of the pre-charging capacitor (101) and the anode of the constant current source (100) are grounded.
Preferably, the method comprises the following steps: the sum of the drain currents of the second output transistor (102) and the first output transistor (103) may be approximated to a total current exhibiting an exponential waveform change with time within a preset time range.
Preferably, the method comprises the following steps: and determining the time constant of the exponential waveform according to the sizes of the constant current source (100) and the pre-charging capacitor (101).
Respectively presetting the same initial voltage value V for two MOS tube grids with the same sizeGS(0) At the beginning of circuit operation, the two MOS transistors 102 and 103 are in the same conduction state in the saturation region, and the initial currents are both I0(neglecting channel length modulation effects).
The 104 tube with smaller size is used as an equivalent capacitor to maintain the working state of the 103 tube, so that the drain current of the 103 tube is always kept as I0。
102 tube has a current of
When in use
While, the OUT terminal outputs current
Thus, the output current at the OUT terminal can be approximated to an exponential waveform.
According to the requirement of the load of the stimulator on the constant output voltage, the square relation between the current in the saturation region and the overdrive voltage and the Taylor approximation mode are applied to obtain the more accurate exponential waveform output pulse. The invention mainly comprises a square relation current generating circuit controlled by a slope voltage generator, which obtains more accurate output current with quadratic relation with time under the condition of constant and controllable input; there is also a constant value current generating circuit in which the gate voltage is constant at a predetermined point. The total output current satisfies the second-order Taylor expansion of the exponential function in a short time range, and the error between the ideal exponential waveform and the total output current is small. The saturation region range of the MOS transistor is larger corresponding to the larger gate voltage range, and the obtained exponential waveform output pulse can obtain a larger dynamic range according to different precharge voltages.
The object of the invention is achieved by the following measures:
fig. 1 is an overall circuit for obtaining exponential current pulses of taylor approximation. The first output transistor 103 and the second output transistor 102 have different operating states but are matched in size.
A. Square relation current generating circuit
The constant current source 100, the pre-charge capacitor 101 and the second output transistor 102 form a saturated region current generating circuit with a ramp generator as a control source. When the control source is in the initial state, the voltage preset value of the pre-charge capacitor 101 by the voltage circuit 105 is preset, and the working state of the circuit is the discharging process of the pre-charge capacitor 101 by the constant current source 100.
B. Constant value current generating circuit
The first output transistor 103 and the equivalent capacitor voltage-controlled transistor 104 constitute a constant-value current generation circuit. When the control source is in an initial state, the voltage preset value of the equivalent capacitor air compression transistor 104 by the voltage circuit 105 is preset, and the circuit working state is maintained in a saturation region of the transistor 104 corresponding to the voltage preset value.
C. Preset voltage circuit
The preset voltage circuit 105 charges the pre-charge capacitor 101 and the equivalent capacitor voltage-controlled transistor 104 uniformly only in the initial state. After the start of operation, the predetermined voltage circuit 105 is disconnected from the current generating circuit.
Example 1
According to the invention, circuit diagram construction is carried out in cadence by applying 0.18 μm technology provided by Taiwan integrated circuit manufacturing company Limited (TSMC), and the feasibility of the circuit design is verified by a simulation means.
The circuit diagram is built according to the structure shown in the first drawing, and a certain value of VDD is given to the OUT end in the simulation process so as to ensure that the second output transistor 102 and the first output transistor 103 work in a saturation region. The pre-charge circuit 105 is used to pre-set the initial voltage values for the capacitors of the two output part generating circuits, and to simplify the configuration, the same initial voltage values are directly pre-set for the initial voltages of the pre-charge capacitor 101 and the equivalent capacitor voltage-controlled transistor 104. Both the simulation time and the setting of the constant current source 100 are referred to the typical pulse width values for the output pulses during the neural stimulation. The result of obtaining output current pulses with different ranges and smaller errors with ideal waveforms can be achieved by setting different pre-charging voltages, and the constant current source 100 and the pre-charging capacitor 101 can adjust the effective output pulse width.
And (3) data output process: in the circuit for obtaining Taylor approximate exponential current pulse, an output end is required to output a relatively ideal exponential waveform, the time constant of the exponential waveform is related to the capacitance values of the constant current source 100 and the pre-charging capacitor 101, the output waveform is subjected to data acquisition and is guided into a CSV file to form an array corresponding to time, and the array is restored into an image on a graphical user interface based on MATLAB.
And comparing the restored image of the output file with an ideal exponential waveform, and calculating the error range of the restored image by using an MATLAB graphic processing tool.
The comparison result shows that the circuit of Taylor approximate exponential current pulse has the characteristics of exquisite design, high precision, strong driving capability and the like. In addition to MATLAB graphical analysis tools, EXCEL graphical tools can also achieve the effect of comparing the output to an ideal waveform.
Claims (3)
1. An exponential waveform current generation circuit based on a CMOS is characterized by comprising a constant current source (100), a pre-charging capacitor (101), a second output transistor (102), a first output transistor (103) and a preset voltage circuit (105), wherein the output end of the preset voltage circuit (105) is respectively connected with the upper plate of the pre-charging capacitor (101) and the upper plate of an MOS transistor capacitor (104); wherein the content of the first and second substances,
the drain electrode of the first output transistor (103) is connected with the drain electrode of the second output transistor (102), the drain electrodes of the first output transistor (103) and the second output transistor (102) are combined to generate total output current, the grid electrode of the first output transistor (103) is connected with the upper plate electrode of an MOS transistor capacitor (104), namely the grid electrode of the MOS transistor capacitor (104), and the lower plate electrode of the MOS transistor capacitor (104), namely the drain electrode, the source electrode and the substrate of the MOS transistor capacitor (104) are all grounded; the source of the first output transistor (103) is grounded;
the grid electrode of the second output transistor (102), the upper plate of the pre-charging capacitor (101) and the cathode of the constant current source (100) are connected; the source of the second output transistor (102), the lower plate of the pre-charging capacitor (101) and the anode of the constant current source (100) are grounded.
2. The CMOS based exponential waveform current generation circuit of claim 1, wherein: the sum of the drain currents of the second output transistor (102) and the first output transistor (103) may be approximated to a total current exhibiting an exponential waveform change with time within a preset time range.
3. The CMOS based exponential waveform current generation circuit of claim 1, wherein: and determining the time constant of the exponential waveform according to the sizes of the constant current source (100) and the pre-charging capacitor (101).
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| CN110568891B (en) * | 2019-09-24 | 2021-07-09 | 上海艾为电子技术股份有限公司 | Current DAC circuit and current output method |
| CN114185385B (en) * | 2021-11-06 | 2023-06-30 | 北京工业大学 | Improved exponential waveform current generation circuit for nerve stimulator |
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| GB9408894D0 (en) * | 1994-05-05 | 1994-06-22 | Secr Defence | Electronic circuit |
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| JP2009194558A (en) * | 2008-02-13 | 2009-08-27 | Toshiba Corp | Current mirror circuit and digital-to-analog conversion circuit |
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| US9176513B2 (en) * | 2014-04-02 | 2015-11-03 | King Fahd University Of Petroleum And Minerals | High dynamic range exponential current generator with MOSFETs |
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