CN113204260B - Multi-channel high-precision current source and working method thereof - Google Patents
Multi-channel high-precision current source and working method thereof Download PDFInfo
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- G05F1/565—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 sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor
- G05F1/567—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 sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor for temperature compensation
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Abstract
The invention discloses a multi-channel high-precision current source, which comprises a controller, a multi-channel DAC, a plurality of V/I conversion circuits, a plurality of load detection circuits, a multi-channel ADC and a temperature sensor, wherein the controller is electrically connected with the multi-channel DAC, two paths of outputs of the multi-channel DAC are electrically connected with the V/I conversion circuits, the ith path of V/I conversion circuit is electrically connected with the ith path of load detection circuit, the number n of the load detection circuits is equal to the number of the V/I conversion circuits, each load detection circuit is electrically connected with one path of input of the multi-channel ADC, the multi-channel ADC is electrically connected with the controller, the temperature sensor is electrically connected with the controller, each path of V/I conversion circuit and the corresponding path of load detection circuit form one path of current source, the input of the current source is two-way output of the multi-channel DAC, and the detection output of the current source is connected to one input of the multi-channel ADC. The invention can solve the technical problem that the existing shimming current source can not meet the high resolution requirement of the nuclear magnetic resonance spectrometer on current control.
Description
Technical Field
The invention belongs to the technical field of nuclear magnetic resonance, and particularly relates to a multichannel high-precision current source for a nuclear magnetic resonance spectrometer and a working method thereof.
Background
NMR spectrometers require that the inhomogeneity of the magnetic field of a superconducting magnet in the measurement region be less than 10 of the main magnetic field-9To achieve this requirement, 20-40 sets of mutually orthogonal coils are often used, and shim current sources are used to apply appropriate currents to the coils so that each set of coils produces mutually orthogonal magnetic fields whose magnitude can be controlled by the currents to counteract the inhomogeneous magnetic field in each direction.
Objectively, the shimming current source needs to meet the following requirements:
1) the circuit number can be provided as much as possible to meet the driving requirements of a plurality of groups of coils, and preferably, 40 groups of current outputs are required;
2) the current output by each group of current sources can be independently controlled to respectively adjust the magnetic field generated by each coil;
3) the adjustment precision of each group of current is as high as possible, fine shimming is realized by finely adjusting the magnitude of the current, and preferably, the current control precision is required to be higher than 20 bits;
4) the current output by each group needs to be kept stable and does not drift, jump and the like along with the change of temperature and time so as to keep the correction magnetic field generated by each group of coils constant;
5) the current output by each group needs to be the same as the set value, and the common bias of the current source needs to be eliminated.
The existing shimming current source generally adopts a controller to control a plurality of 16-bit precision Digital-to-analog converters (DACs), each DAC has 1-4 output channels, and each channel drives a V/I conversion circuit composed of an operational amplifier, a triode and the like to convert the voltage value output by the DAC into an output current. However, the V/I conversion circuit has a natural bias, so that there is a deviation between the actual output current and the set current. In order to eliminate the bias current, the quiescent current output by each current source is manually measured one by one through a meter, the value is converted into a corresponding DAC setting value (namely, a bias value), and the corresponding bias value is deducted when the DAC configuration value of the corresponding channel is set.
However, the existing shimming current sources have some non-negligible technical drawbacks:
(1) the 16-bit precision does not meet the requirement of a nuclear magnetic resonance spectrometer on high-precision current control, and particularly when the output current is greater than 1A, the adjustment precision can only reach 30 uA;
(2) the V/I conversion circuit composed of 1-4 paths of DACs and operational amplifiers, triodes and the like is large in size, and occupies a large space when 40 groups of current sources are built;
(3) different output biases exist in components used by the current sources, so that different bias currents exist in the output currents of all paths of current sources, the bias currents can change along with factors such as aging of the components, the change condition of the bias currents cannot be accurately reflected in real time in actual operation through a method of manually measuring static currents and recording corresponding configuration values, and unequal deviations always exist between the actually output currents and the set currents;
(4) the current output by each current source is affected by the temperature coefficient of the used components, the actually output current gradually drifts, and the actually output current deviates from the initial set current more and more after working for a period of time.
Disclosure of Invention
The invention provides a multi-channel high-precision current source for a nuclear magnetic resonance spectrometer and a working method thereof, aiming at solving the technical problems that the existing shimming current source does not meet the high-resolution requirement of the nuclear magnetic resonance spectrometer on high-precision current control, occupies larger space, has different output bias due to different components, has different deviation between the current actually output by each current source and the set current, and gradually drifts the current output by each current source due to the temperature drift characteristics of each component after working for a period of time.
In order to achieve the above object, according to one aspect of the present invention, there is provided a multi-channel high-precision current source, comprising a controller, a multi-channel DAC, a plurality of V/I conversion circuits, a plurality of load detection circuits, a multi-channel ADC, and a temperature sensor, wherein the controller is electrically connected to the multi-channel DAC, and two outputs of the multi-channel DAC are electrically connected to each V/I conversion circuit;
the ith V/I conversion circuit is electrically connected with the ith load detection circuit, the number n of the load detection circuits is equal to the number of the V/I conversion circuits, wherein n is any natural number and belongs to [1, n ];
each load detection circuit is electrically connected with one input of the multi-channel ADC;
the multichannel ADC is electrically connected with the controller, and the temperature sensor is electrically connected with the controller.
Each path of V/I conversion circuit and a corresponding path of load detection circuit form a path of current source, the input of the current source is two paths of output of the multi-channel DAC, and the detection output of the current source is connected with one path of input of the multi-channel ADC.
Preferably, the multi-channel DAC is one or more 16-bit DACs, each DAC is independently connected with the controller, and the multi-channel DAC has 2n paths of outputs in total;
the multichannel ADC can be one or more ADCs, the total number of input lines is larger than or equal to the number n of current supply lines, each ADC is independently connected with the controller 1, and the digital resolution of each ADC is larger than the target resolution of the current supply.
Preferably, each V/I conversion circuit comprises a multi-channel power operational amplifier, a first resistor, a second resistor, and a third resistor;
two paths of outputs of the multi-channel DAC are respectively and electrically connected with one ends of a first resistor and a second resistor, one end of a third resistor and the other ends of the first resistor and the second resistor are electrically connected with the input end of the multi-channel power operational amplifier;
the multi-channel power operational amplifier is electrically connected with the other end of the third load resistor through the load detection circuit;
the load detection circuit is also electrically connected with one input of the multi-channel ADC;
the multi-channel power operational amplifier comprises a plurality of power operational amplifiers which are arranged independently;
each V/I conversion circuit uses one power operational amplifier in the multi-channel power operational amplifier, namely the multi-channel power operational amplifier is shared by a plurality of current sources.
Preferably, the load detection circuit comprises a sampling resistor, a load, and an instrumentation amplifier;
the output end of the load is grounded;
the output end of the V/I conversion circuit is electrically connected with the input end of the load through a sampling resistor;
one end of the sampling resistor connected with the load is electrically connected with the cathode of the instrument amplifier;
one end of the sampling resistor connected with the V/I conversion circuit is electrically connected with the anode of the instrument amplifier;
the output end of the instrument amplifier is used as the output end of the load detection circuit.
Preferably, the load detection circuit comprises a sampling resistor and a load;
one end of the sampling resistor is grounded, and the other end of the sampling resistor is electrically connected with the load;
one end of the sampling resistor connected with the load is used as the output end of the load detection circuit;
the output end of the V/I conversion circuit is electrically connected with a load;
preferably, the controller is configured to control each output voltage of the multi-channel DAC according to a current setting value of each current source, and further drive each V/I conversion circuit to output a current proportional to or inversely proportional to the current setting value to the load, where the current output by the ith V/I conversion circuit is:
wherein k is1＝R1/R0，k2＝R2/R0，R0Represents the resistance value, R, of the third resistor 341Represents the resistance value, R, of the first resistor 322Represents the resistance value, R, of the second resistor 33sRepresents the resistance value, V, of the sampling resistor 411The voltage is output by the first path of the multi-channel DAC 2; v2A voltage output for the second path of the multi-channel DAC2 and having k1≥26·k2。
Preferably, the precision of the multi-channel DAC is 16 bits, and the resolution when the first output voltage of the multi-channel DAC controls the current source to output current is:
Ires1＝Imax/216
the resolution ratio when the second output voltage of the multi-channel DAC controls the current source to output current is as follows:
Ires2＝Imax/216+m
wherein, ImaxM is the number of bits of the voltage control current output by the 2 nd-cnt 1 path of the multi-channel DAC with higher precision than that of the voltage control current output by the (2 x-cnt 1-1) path of the multi-channel DAC, and is the current output by the V/I conversion circuit when the voltage output by the first path DAC2 is maximum.
Preferably, the multi-channel ADC is configured to collect a voltage output by each load detection circuit, perform analog-to-digital conversion on the voltage, and transmit a voltage conversion result to the controller;
the controller is also used for comparing the voltage conversion result with a current setting value, regulating the voltage output by the two paths of the multi-channel DA, further regulating the current output by the current source, collecting the voltage conversion result output by each path of the load detection circuit again, comparing the voltage conversion result with the current setting value again, …, and repeatedly executing the process until the final voltage conversion result is equal to the current setting value.
Preferably, the temperature sensor is used for monitoring the working temperature t of the whole multi-channel high-precision current source and sending the monitored working temperature t to the controller;
the controller is further used for inquiring a preset temperature coefficient correction table of each current source according to the working temperature to obtain a temperature correction coefficient corresponding to the working temperature t, and calculating a current setting value of each current source by using the temperature correction coefficient, wherein the current setting value is further used for adjusting the output current of each current source, so that the temperature drift of the output current of each current source is corrected.
In general, the above current source contemplated by the present invention can achieve the following advantages compared to the prior art:
1. because the two paths of output of the DAC are used for controlling one path of current source, the precision of the second path of output control current of the DAC is set to be m bits higher than that of the first path of output control current of the DAC, so that the current control precision of each path of current source reaches 16+ m bits, and the problem that the 16-bit control precision in the prior art cannot meet the requirement of high-precision current control of a nuclear magnetic resonance spectrometer can be solved;
2. since the current source of the present invention includes a plurality of high power operational amplifiers independently arranged from each other on a single chip, and using a single chip with multi-path output DAC as the driving input of each current source, using a single chip with multi-path input ADC to collect the monitoring output of each current source, using two paths of output voltage of each DAC, one path of high-power operational amplification in each high-power operational amplifier, and one path of input of each multi-path input ADC for each current source, and one high-power operational amplifier is used to replace a plurality of discrete components for constructing the current source, such as the operational amplifier, the triode and the like, so that the volume of the current source is reduced, therefore, the problems that in the prior art, a 1-4 channel DAC and a V/I conversion circuit composed of an operational amplifier and a triode are large in size, and when 40 paths of current sources are arranged, a large space is occupied are solved.
According to another aspect of the present invention, there is provided a method for operating the above-mentioned multi-channel high-precision current source, comprising the steps of:
(1) the controller sets the counter cnt1 to 1;
(2) the controller sets the counter cnt2 to 1;
(3) the controller controls the temperature sensor to monitor the working temperature t of the whole multichannel high-precision current source, and temperature correction coefficients a and b corresponding to the working temperature t of a cnt 1-th current source are searched in a pre-established temperature coefficient correction table;
(4) the controller calculates an output current target value of the cnt 1-th current source according to the temperature correction coefficients a and b obtained in the step (3):
D′set＝a·Dset+b
wherein DsetIndicates a preset output current configuration value, D, of the cnt1 th current sourcesetThe binary digit number of the ADC is the same as the digital resolution of the multi-channel ADC;
(5) the controller calculates a voltage configuration value D output by the (2 x cnt1-1) th path of the multi-channel DAC according to the output current target value of the cnt1 th path current source1And the voltage configuration value D output by the 2 nd-cnt 1 th path of the multi-channel DAC2：
D1＝Int(D′set/215)
D2＝[D′set-Int(D′set/215)]×2m
Wherein Int represents a down-rounding operation, and m is the number of bits of precision of the voltage control current output by the 2 nd × cnt1 th path of the multi-channel DAC, which is higher than that of the voltage control current output by the (2 nd × cnt1-1) th path of the multi-channel DAC;
(6) the controller determines the voltage configuration value D2Whether or not the absolute value of (A) is greater than 215If yes, entering the step (7), otherwise, entering the step (8);
(7) the controller outputs a voltage configuration value D to the (2 x cnt1-1) th path of the multi-channel DAC obtained in the step (5)1And the voltage configuration value D output by the 2 nd-cnt 1 th path of the multi-channel DAC2Performing self-updating operation:
D1＝D1+Int(D2/215)
D2not less than 0 then D2＝D2-215
D2<0 then D2＝D2+215
(8) The controller sets the voltage of the (2 x cnt1-1) th path output of the multi-channel DAC to be a voltage configuration value D1And setting the voltage output by the 2 × cnt1 path of the multi-channel DAC as the voltage configuration value D2；
(9) The controller controls the multichannel ADC to acquire the voltage output by the cnt1 th load detection circuit, performs analog-to-digital conversion on the voltage, and judges an analog-to-digital conversion result DoutAnd an output current target value D'setWhether the absolute value of the difference value is smaller than a preset threshold value or not, if so, entering a step (12), and if not, entering a step (10);
(10) the controller sets cnt2 to cnt2+1, and judges whether cnt2 is smaller than a preset iteration threshold, if so, the step (11) is carried out, otherwise, the step (12) is carried out;
(11) the voltage configuration value D output by the controller to the 2 nd-cnt 1 path of the multi-channel DAC2Carrying out updating operation and returning to the step (6):
D2＝D2+Dir×(Dout-D′set)
in the formula, Dir is a preset direction control value of error feedback, and the value is 1 or-1.
(12) The controller sets cnt1 to cnt1+1 and determines whether cnt1 is greater than the total number n of load sense circuits, if so, the process ends, otherwise returns to step (2).
In general, compared with the prior art, the above working method contemplated by the present invention can achieve the following beneficial effects:
1. because the working method of the invention adopts the steps (6) to (11), the current monitoring value output by each current source is acquired through the high-resolution ADC, the error between the current monitoring value and the current set value is calculated, the first output or the second output of the DAC is set to adjust the output current, and iteration is carried out continuously, so that the error between the current monitoring value and the current set value is smaller than the threshold value, the current output by each current source is continuously adjusted, the current output by each current source is the same as the set value and is kept constant, therefore, the working method can solve the problems that the change condition of the bias current cannot be accurately reflected in real time in the actual operation by the method of manually measuring the quiescent current and recording the corresponding configuration value in the prior art, and unequal deviation exists between the actually output current and the set current;
2. the working method of the invention adopts the steps (3) to (11), the temperature of the whole system is monitored by arranging the temperature sensor, the temperature coefficient table of the current source is stored in the controller, the controller reads the temperature coefficient correction value according to the real-time temperature, and the temperature coefficient correction value is used for carrying out temperature correction on the setting value of the output current of each current source, so that the output current of each current source is kept unchanged at different temperatures, therefore, the working method can solve the problems that the current output by each current source in the prior art is influenced by the temperature coefficient of the used components, the actually output current can drift gradually, and the actually output current deviates from the initial set current after working for a period of time.
Drawings
FIG. 1 is a block circuit diagram of a multi-channel high precision current source of the present invention;
FIG. 2 is a detailed circuit block diagram of the V/I conversion circuit of the present invention;
FIG. 3 is a block circuit diagram of a load detection circuit of the present invention;
FIG. 4 is a circuit block diagram of another load detection circuit of the present invention;
fig. 5 is a flow chart of the method of operation of the multi-channel high precision current source of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The basic idea of the invention is to provide a multichannel high-precision current source for a nuclear magnetic resonance spectrometer, wherein one path of current source is controlled by two paths of output voltages of a 16-bit precision DAC, and the precision of the second path of output voltage regulating current of the DAC is set to be at least 6 bits higher than that of the first path of output voltage regulating current of the DAC, so that the regulating precision of each path of current source is higher than 21 bits; on the other hand, the current source is constructed by using a DAC with 20-40 paths of outputs on a single chip, a high-power operational amplifier with multiple paths of outputs on a single chip and an ADC with 20-40 paths of inputs on a single chip, namely, the multiple current sources share one DAC, one ADC and one high-power operational amplifier, so that the size of the current source is reduced; on the other hand, the current value output by each current source is monitored by setting the high-precision ADC, the error between the current value monitored by each current source and the current set value is calculated by the controller, and the output voltage of the first path or the second path of the DAC is adjusted to adjust the output current so that the error between the output current and the set current is smaller than the set threshold value; meanwhile, the drift of the output current can be quickly corrected by uninterruptedly monitoring and adjusting the output current of each current source, and the current bias caused by the characteristic change of components, the voltage change of a power supply and the like is eliminated; and finally, a temperature sensor is arranged to monitor the temperature of the whole multi-channel high-precision current source, a temperature correction coefficient table of each current source is stored in the controller, and the controller reads the temperature correction coefficient according to the real-time temperature and performs temperature correction on the set value of the output current so as to eliminate drift of the output current of each current source due to temperature change.
As shown in fig. 1, the present invention provides a multi-channel high-precision current source, which includes a controller 1, a multi-channel DAC2, a plurality of Voltage-current (V/I) conversion circuits 3, a plurality of load detection circuits 4, a multi-channel ADC 5, and a temperature sensor 6.
The controller 1 is electrically connected with the multi-channel DAC2, two paths of outputs of the multi-channel DAC2 are electrically connected with the V/I conversion circuits 3, each path (i.e. I-th path) of the V/I conversion circuit 3 is electrically connected with each path (i.e. I-th path) of the load detection circuit 4, the number n of the load detection circuits 4 is equal to the number of the V/I conversion circuits 3, wherein n is any natural number and is e to [1, n ], each load detection circuit 4 is electrically connected with one path of input of the multi-channel ADC 5, the multi-channel ADC 5 is electrically connected with the controller 1, and the temperature sensor 6 is electrically connected with the controller 1.
Each path of V/I conversion circuit 3 and a corresponding path of load detection circuit 4 form a path of current source, the input of the current source is two paths of output of the multi-channel DAC2, and the detection output of the current source is connected to one path of input of the multi-channel ADC 5.
It should be noted that in the present invention, the multi-channel DAC2 may be one or more 16-bit DACs, and the multi-channel DAC2 has 2n outputs in total, and each DAC is individually connected to the controller 1.
Further preferably, in the present embodiment, the multi-channel DAC2 is a DAC comprising a chip integrated 40-way output, and the digital resolution of the DAC is 16 bits.
It should be noted that, in the present invention, the multi-channel ADC 5 may be one or more ADCs, the total number of input channels is ≧ the number n of current source channels, each ADC is individually connected to the controller 1, and the digital resolution of the ADC is greater than the target resolution of the current source.
As a further preference, in the present embodiment, the multichannel ADC 5 includes three-chip ADCs, the target resolution of the current source is 20 bits, and the digital resolution of the ADC is 32 bits.
As shown in fig. 2, each V/I conversion circuit 3 includes a multi-channel power op amp 31, a first resistor 32, a second resistor 33, and a third resistor 34.
Two paths of outputs of the multi-channel DAC2 are respectively and electrically connected with one ends of a first resistor 32 and a second resistor 33, one end of a third resistor 34 and the other ends of the first resistor 32 and the second resistor 33 are electrically connected with an input end of a multi-channel power operational amplifier 31, the multi-channel power operational amplifier 31 is electrically connected with the other end of the load third resistor 34 through a load detection circuit 4, and the load detection circuit 4 is further electrically connected with one path of input of a multi-channel ADC 5.
It should be noted that, in the present invention, a multi-channel power op-amp 31 includes a plurality of power op-amps which are arranged independently from each other, and each V/I conversion circuit 3 uses one power op-amp in the multi-channel power op-amp 31, that is, the multi-channel power op-amp 31 is shared by multiple current sources.
As a further preference, in the present embodiment, the multi-channel power operational amplifier 31 includes two power operational amplifiers.
As shown in fig. 3, according to one embodiment, the load detection circuit 4 of the present invention includes a sampling resistor 41, a load 42, and an instrumentation amplifier 43, an output terminal of the load 42 is grounded, an output terminal of the V/I conversion circuit 3 is electrically connected to an input terminal of the load 42 through the sampling resistor 41, one end of the sampling resistor 41 connected to the load 42 is electrically connected to a negative electrode of the instrumentation amplifier 43, one end of the sampling resistor 41 connected to the V/I conversion circuit 3 is electrically connected to a positive electrode of the instrumentation amplifier 43, and an output terminal of the instrumentation amplifier 43 serves as an output terminal of the load detection circuit 4.
As shown in fig. 4, according to another embodiment, the load detection circuit 4 of the present invention includes a sampling resistor 41 and a load 42, one end of the sampling resistor 41 is grounded, the other end of the sampling resistor 41 is electrically connected to the load 42, one end of the sampling resistor 41 connected to the load 42 serves as an output end of the load detection circuit 4, and an output end of the V/I conversion circuit 3 is electrically connected to the load 42.
It is noted that in this embodiment, the load 42 is a shim coil.
It should be noted that, in the present invention, the resistance of the sampling resistor 41 included in all the load detection circuits may be different or the same, and the resistance of the load 42 is also the same.
In the present invention, the resistance of the first resistor 32 included in all the V/I conversion circuits may be different or the same, as well as the second resistor 33 and the third resistor 34.
In the present embodiment, the resistance value of the first resistor 32 is 20K Ω;
the resistance value of the second resistor 33 is greater than or equal to 1.28 MOmega;
the resistance of the third resistor 34 is 1K Ω;
the resistance value of the sampling resistor 41 ranges from 0.1 Ω to 10 Ω;
the resistance of load 42 ranges from 1 Ω to 300 Ω.
The controller 1 controls each output voltage of the multi-channel DAC2 according to the current setting value of each current source, and further drives each V/I conversion circuit to output a current which is in direct proportion or inverse proportion to the current setting value to the load 42.
Specifically, the current output by the ith V/I conversion circuit is:
in the formula: k is a radical of1＝R1/R0，k2＝R2/R0Wherein R is0Represents the resistance value, R, of the third resistor 341Represents the resistance value, R, of the first resistor 322Represents the resistance value, R, of the second resistor 33sRepresents the resistance value, V, of the sampling resistor 411The voltage is output by the first path of the multi-channel DAC 2; v2The voltage output by the second path of the multi-channel DAC 2.
Wherein k is1≥26·k2The purpose of this is to make the multi-channel DAC2 output the voltage control current I in the second pathiThe first output voltage of the multi-channel DAC2 controls the current IiIs high in precision by at least m bits (i.e. 2)mMultiple).
It should be noted that, in the present invention, the precision of the multi-channel DAC2 is 16 bits, and the resolution when the first output voltage of the multi-channel DAC2 controls the current source output current is:
Ires1＝Imax/216
the resolution ratio when the second path of output voltage of the multi-channel DAC2 controls the current source to output current is as follows:
Ires2＝Imax/216+m
wherein, ImaxThe current output by the V/I conversion circuit when the first output voltage of the DAC2 is maximum is obtained. The current precision of the current source output controlled by the first output voltage of the DAC2 and the second output voltage of the DAC2 is 16+ m bits (including the direction control bit).
In this embodiment, m is 6, and the current precision of the current source output is 22 bits.
The multi-channel ADC 5 is configured to collect the voltage output by each load detection circuit 4, perform analog-to-digital conversion on the voltage, and transmit the voltage conversion result to the controller 1, where the controller 1 compares the voltage conversion result with the current setting value, adjusts the voltage output by the multi-channel DAC2, further adjusts the current output by the current source (which is based on the above formula), collects the voltage conversion result output by each load detection circuit 4 again, compares the voltage conversion result with the current setting value again, and … repeatedly executes the process until the final voltage conversion result is equal to the current setting value (or the error between the voltage conversion result and the current setting value is smaller than the threshold).
The temperature sensor 6 is used for monitoring the working temperature t of the whole multichannel high-precision current source and sending the monitored working temperature t to the controller 1, the controller 1 queries a preset temperature coefficient correction table of each current source according to the working temperature to obtain a temperature correction coefficient corresponding to the working temperature t, and calculates a current setting value of each current source by using the temperature correction coefficient, and the current setting value is further used for adjusting the output current of each current source (which is based on the formula), so that the temperature drift of the output current of each current source is corrected.
In the present embodiment, the temperature coefficient correction table is created according to the following procedure:
(1) setting the output of each current source as a fixed current output;
(2) placing each current source in a stable and adjustable temperature environment;
(3) recording an environment temperature value and an output current value of each current source;
(4) changing the environment temperature, and recording a new environment temperature value and a current value output by each current source until the environment temperature covers all working temperature ranges;
(5) and making a linear fitting curve between the output current of each current source and the ambient temperature, and recording a proportionality coefficient a and an offset coefficient b in a fitting formula as a temperature correction coefficient table of the current source.
As shown in fig. 5, the present invention further provides a working method of the multi-channel high-precision current source, which comprises the following steps:
(1) the controller sets the counter cnt1 to 1;
(2) the controller sets the counter cnt2 to 1;
(3) the controller controls the temperature sensor to monitor the working temperature t of the whole multichannel high-precision current source, and temperature correction coefficients a and b corresponding to the working temperature t of a cnt 1-th current source are searched in a pre-established temperature coefficient correction table;
(4) the controller calculates an output current target value of the cnt 1-th current source according to the temperature correction coefficients a and b obtained in the step (3):
D′seh＝a·Dset+b
wherein DsetIndicates a preset output current configuration value, D, of the cnt1 th current sourcesetThe binary digit number of the ADC is the same as the digital resolution of the multi-channel ADC;
in this embodiment, DsetThe number of binary digits of (a) is 32 bits.
(5) The controller calculates a voltage configuration value D output by the (2 x cnt1-1) th path of the multi-channel DAC according to the output current target value of the cnt1 th path current source1And the voltage configuration value D output by the 2 nd-cnt 1 th path of the multi-channel DAC2：
D1＝Int(D′set/215)
D2＝[D′set-Int(D′set/215)]×2m
Wherein Int represents a down-rounding operation, and m is a number of bits where the precision of the voltage control current output from the 2 nd cnt1 th path of the multi-channel DAC is higher than that of the voltage control current output from the (2 nd cnt1-1) th path of the multi-channel DAC, and in the embodiment, m is 6;
(6) the controller determines the voltage configuration value D2Whether or not the absolute value of (A) is greater than 215If yes, entering the step (7), otherwise, entering the step (8);
(7) the controller outputs a voltage configuration value D to the (2 x cnt1-1) th path of the multi-channel DAC obtained in the step (5)1And the voltage configuration value D output by the 2 nd-cnt 1 th path of the multi-channel DAC2Performing self-updating operation:
D1＝D1+Int(D2/215)
D2not less than 0 then D2＝D2-215
D2<0 then D2＝D2+215
(8) The controller sets the voltage of the (2 x cnt1-1) th path output of the multi-channel DAC to be a voltage configuration value D1And setting the voltage output by the 2 × cnt1 path of the multi-channel DAC as the voltage configuration value D2；
It should be noted that if the step (7) is skipped to the step (8), the voltage configuration value D is set1Is the voltage configuration value D after self-updating in the step (7)1Voltage configuration value D2Is the voltage configuration value D after self-updating in the step (7)2。
(9) The controller controls the multichannel ADC to acquire the voltage output by the cnt1 th load detection circuit, performs analog-to-digital conversion on the voltage, and judges an analog-to-digital conversion result DoutAnd an output current target value D'setWhether the absolute value of the difference value is smaller than a preset threshold value or not, if so, entering a step (12), and if not, entering a step (10);
specifically, the preset threshold is less than 2048 (2)11) Preferably 1024.
(10) The controller sets cnt2 to cnt2+1, and judges whether cnt2 is smaller than a preset iteration threshold, if so, the step (11) is carried out, otherwise, the step (12) is carried out;
specifically, the iteration threshold value in this step is an integer ranging from 1 to 10, preferably 10.
(11) The voltage configuration value D output by the controller to the 2 nd-cnt 1 path of the multi-channel DAC2Carrying out updating operation and returning to the step (6):
D2＝D2+Dir×(Dout-D′set)
in the formula, Dir is a preset direction control value of error feedback, and the value is 1 or-1.
(12) The controller sets cnt1 to cnt1+1 and determines whether cnt1 is greater than the total number n of load sense circuits, if so, the process ends, otherwise returns to step (2).
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. A working method of a multi-channel high-precision current source comprises a controller, a multi-channel DAC, a plurality of V/I conversion circuits, a plurality of load detection circuits, a multi-channel ADC and a temperature sensor, wherein the controller is electrically connected with the multi-channel DAC, two paths of outputs of the multi-channel DAC are electrically connected with the V/I conversion circuits, the ith V/I conversion circuit is electrically connected with the ith load detection circuit, the number n of the load detection circuits is equal to the number of the V/I conversion circuits, n is any natural number and belongs to [1, n ], each load detection circuit is electrically connected with one path of input of the multi-channel ADC, the multi-channel ADC is electrically connected with the controller, the temperature sensor is electrically connected with the controller, and each path of V/I conversion circuit and one path of corresponding load detection circuit form one path of current source, the input of the current source is two-way output of the multi-channel DAC, and the detection output of the current source is connected to one-way input of the multi-channel ADC, and the working method is characterized by comprising the following steps:
(1) the controller sets the counter cnt1 to 1;
(2) the controller sets the counter cnt2 to 1;
(3) the controller controls the temperature sensor to monitor the working temperature t of the whole multichannel high-precision current source, and temperature correction coefficients a and b corresponding to the working temperature t of a cnt 1-th current source are searched in a pre-established temperature coefficient correction table;
(4) the controller calculates an output current target value of the cnt 1-th current source according to the temperature correction coefficients a and b obtained in the step (3):
D′set＝a·Dset+b
wherein DsetIndicates a preset output current configuration value, D, of the cnt1 th current sourcesetThe binary digit number of the ADC is the same as the digital resolution of the multi-channel ADC;
(5) the controller calculates a voltage configuration value D output by the (2 x cnt1-1) th path of the multi-channel DAC according to the output current target value of the cnt1 th path current source1And voltage configuration value D output by 2 × cntl path of multi-channel DAC2：
D1＝Int(D′set/215)
D2＝[D′set-Int(D′set/215)]×2m
Wherein Int represents a down-rounding operation, and m is the number of bits of precision of the voltage control current output by the 2 nd × cnt1 th path of the multi-channel DAC, which is higher than that of the voltage control current output by the (2 nd × cnt1-1) th path of the multi-channel DAC;
(6) the controller determines the voltage configuration value D2Whether or not the absolute value of (A) is greater than 215If yes, entering the step (7), otherwise, entering the step (8);
(7) the controller outputs a voltage configuration value D to the (2 x cnt1-1) th path of the multi-channel DAC obtained in the step (5)1And the voltage configuration value D output by the 2 nd-cnt 1 th path of the multi-channel DAC2Performing self-updating operation:
D1＝D1+Int(D2/215)
D2not less than 0 then D2＝D2-215
D2< 0 then D2＝D2+215
(8) The controller will have moreThe voltage output by the (2 x cnt1-1) th path of the channel DAC is set as a voltage configuration value D1And setting the voltage output by the 2 × cnt1 path of the multi-channel DAC as the voltage configuration value D2；
(9) The controller controls the multichannel ADC to acquire the voltage output by the cnt1 th load detection circuit, performs analog-to-digital conversion on the voltage, and judges an analog-to-digital conversion result DoutAnd an output current target value D'setWhether the absolute value of the difference value is smaller than a preset threshold value or not, if so, entering a step (12), and if not, entering a step (10);
(10) the controller sets cnt2 to cnt2+1, and judges whether cnt2 is smaller than a preset iteration threshold, if so, the step (11) is carried out, otherwise, the step (12) is carried out;
(11) the controller outputs a voltage configuration value D to a 2 × cntl path of the multi-channel DAC2Carrying out updating operation and returning to the step (6):
D2＝D2+Dir×(Dout-D′set)
in the formula, Dir is a preset direction control value of error feedback, and the value is 1 or-1;
(12) the controller sets cnt1+1 to cnt1 and determines whether it is greater than the total number n of load detection circuits, if so, the process ends, otherwise, it returns to step (2).
2. The method of operating a multi-channel high precision current source according to claim 1,
the multi-channel DAC is one or more 16-bit DACs, each DAC is independently connected with the controller, and the multi-channel DAC has 2n paths of outputs in total;
the multichannel ADC can be one or more ADC, the total input path number of the multichannel ADC is more than or equal to the current source path number n, each ADC is independently connected with the controller 1, and the digital resolution of each ADC is more than the target resolution of the current source.
3. Method of operating a multi-channel high precision current source according to claim 1 or 2,
each V/I conversion circuit comprises a multi-channel power operational amplifier, a first resistor, a second resistor and a third resistor;
two paths of outputs of the multi-channel DAC are respectively and electrically connected with one ends of a first resistor and a second resistor, one end of a third resistor and the other ends of the first resistor and the second resistor are electrically connected with the input end of the multi-channel power operational amplifier;
the multi-channel power operational amplifier is electrically connected with the other end of the third load resistor through the load detection circuit;
the load detection circuit is also electrically connected with one input of the multi-channel ADC;
the multi-channel power operational amplifier comprises a plurality of power operational amplifiers which are arranged independently;
each V/I conversion circuit uses one power operational amplifier in the multi-channel power operational amplifier, namely the multi-channel power operational amplifier is shared by a plurality of current sources.
4. The method of operating a multi-channel high precision current source according to claim 3,
the load detection circuit comprises a sampling resistor, a load and an instrument amplifier;
the output end of the load is grounded;
the output end of the V/I conversion circuit is electrically connected with the input end of the load through a sampling resistor;
one end of the sampling resistor connected with the load is electrically connected with the cathode of the instrument amplifier;
one end of the sampling resistor connected with the V/I conversion circuit is electrically connected with the anode of the instrument amplifier;
the output end of the instrument amplifier is used as the output end of the load detection circuit.
5. The method of operating a multi-channel high precision current source according to claim 3,
the load detection circuit comprises a sampling resistor and a load;
one end of the sampling resistor is grounded, and the other end of the sampling resistor is electrically connected with the load;
one end of the sampling resistor connected with the load is used as the output end of the load detection circuit;
the output end of the V/I conversion circuit is electrically connected with a load.
6. The operating method of the multi-channel high-precision current source according to claim 4 or 5, wherein the controller is configured to control each output voltage of the multi-channel DAC according to the current setting value of each current source, and further drive each V/I converting circuit to output a current proportional or inverse proportional to the current setting value to the load, where the current output by the ith V/I converting circuit is:
wherein k is1＝R1/R0，k2＝R2/R0，R0Representing the resistance of the third resistor, R1Representing the resistance of the first resistor, R2Representing the resistance of the second resistor, RsRepresenting the resistance, V, of the sampling resistor1The voltage is output by the first path of the multi-channel DAC; v2A voltage output for the second path of the multi-channel DAC and having k1≥26·k2。
7. The method of operating a multi-channel high precision current source according to claim 6,
the precision of the multi-channel DAC is 16 bits, and the resolution ratio when the first output voltage of the multi-channel DAC controls the current source to output current is as follows:
Ires1＝Imax/216
the resolution ratio when the second output voltage of the multi-channel DAC controls the current source to output current is as follows:
IreS2＝Imax/216+m
wherein, ImaxM is the number of bits of the voltage control current output by the 2 nd x cnt1 path of the multi-channel DAC, which is the current output by the V/I conversion circuit when the voltage output by the first path of DAC2 is maximum, and is higher than the precision of the voltage control current output by the (2 x cnt1-1) path of the multi-channel DAC.
8. The method of operating a multi-channel high precision current source according to claim 7,
the multichannel ADC is used for collecting the voltage output by each load detection circuit, performing analog-to-digital conversion on the voltage and transmitting the voltage conversion result to the controller;
the controller is also used for comparing the voltage conversion result with a current setting value, adjusting the voltage output by the multi-channel DAC, further adjusting the current output by the current source, acquiring the voltage conversion result output by each load detection circuit again, comparing the voltage conversion result with the current setting value again, and repeatedly executing the process until the final voltage conversion result is equal to the current setting value.
9. The method of operating a multi-channel high precision current source according to claim 7,
the temperature sensor is used for monitoring the working temperature t of the whole multi-channel high-precision current source and sending the monitored working temperature t to the controller;
the controller is further used for inquiring a preset temperature coefficient correction table of each current source according to the working temperature to obtain a temperature correction coefficient corresponding to the working temperature t, and calculating a current setting value of each current source by using the temperature correction coefficient, wherein the current setting value is further used for adjusting the output current of each current source, so that the temperature drift of the output current of each current source is corrected.
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Denomination of invention: A multi-channel high-precision current source and its working method Granted publication date: 20220301 Pledgee: Qingshan Branch of Wuhan Rural Commercial Bank Co.,Ltd. Pledgor: WUHAN ZHONGKE NIUJIN WAVE SPECTRUM TECHNOLOGY CO.,LTD. Registration number: Y2024980037072 |