CN101629973B - High-precision current sampling circuit without operational amplifier for low voltage power supply - Google Patents
High-precision current sampling circuit without operational amplifier for low voltage power supply Download PDFInfo
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- CN101629973B CN101629973B CN2009100436414A CN200910043641A CN101629973B CN 101629973 B CN101629973 B CN 101629973B CN 2009100436414 A CN2009100436414 A CN 2009100436414A CN 200910043641 A CN200910043641 A CN 200910043641A CN 101629973 B CN101629973 B CN 101629973B
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Abstract
Current sampling circuits are widely applied in various integrated circuits taking current as a medium; along with the continuous improvement of the technical level of the integrated circuit, power supply voltage continuously lowers, and traditional current sampling structure is not suitable for application of integrated circuit for low voltage power supply. The invention discloses a high-precision current sampling circuit for switch power source control loops, adopts a current mirror structure to replace an operational amplifier, simplifies circuit structure, utilizes microampere-level fixed bias to improve the response speed of the current sampling circuit, and actively corrects sampling errors led in by the fixed bias and improves sampling precision. The circuit is composed of a main body structure, basic bias, current-voltage sampling output, fixed bias compensation, a current tube and sampling switch and an external load.
Description
Technical field
The invention belongs to the integrated circuit (IC) design field, be used for accurately sampling by transistorized electric current, be specifically related to a kind of suitable low voltage power supply occasion, not needs operational amplifier, high-precision current sampling circuit simple in structure.
Background technology
The current sample technology is the gordian technique in Controlled in Current Mode and Based loop and the current protecting circuit; utilizing electric current to form in the integrated circuit of closed-loop control; the current sample circuit ingredient that is absolutely necessary; especially in the Switching Power Supply adhesive integrated circuit of Current Feedback Control, the performance of current sampling circuit is directly connected to the performance of circuit integral body.
Modal in the method for current sample is to be sampled on the current path the directly sampling resistor of a little resistance of series connection, obtains electric current by the tube of current that is sampled from the pressure drop of resistance.This method is simple, but sampling resistor is connected on the main current path merchant, can consume a large amount of power, reduces the work efficiency of entire chip, and along with the reduction of output voltage, the proportion in the power consumption of the power that sampling resistor consumed in entire chip can further strengthen.
For fear of the influence of sampling resistor to the electric current output channel, the method that adopts current potential to duplicate usually.It among Fig. 1 a kind of current sample method that adopts the amplifier structure, this method is utilized the characteristic of operational amplifier input end " empty short ", the drain terminal voltage that is sampled tube of current MP1 " is duplicated " drain terminal of sampling pipe MP2, because it is identical with the channel length that is sampled tube of current MP1 to constitute the sampling pipe MP2 of current mirror, width is proportional to be dwindled, therefore MP2 can be accurately in proportion mirror image flow through the electric current of tube of current MP1, thereby realize current sample.The width ratio that might as well suppose MP1 and MP2 pipe is M, and basic bias current is Ib, and circuit is IL to the output current of load, and the induction current that sampling obtains is Isense, and the proportionate relationship according to the current mirror that is made of MP1 and MP2 can obtain equation (1) so.
I
L＝M×I
sense+(M-1)×I
b (1)
Polynomial first is desirable proportional current sampling relation in the equation (1), and second is sampling error, so the current sample precision of this circuit is equation (2).As seen there is intrinsic sampling error in this circuit, and this error constantly increases along with reducing of tube of current output current.In addition, owing to the existence of operational amplifier, strengthened the difficulty of circuit design, the gain of operational amplifier and response speed are directly connected to the precision and the response speed of whole-sample.And, in this circuit, from the power supply to ground, there is the transistor of 4 grades of series connection at most, this just makes in can not the working power voltage lower circuit of this circuit.
For fear of the sensing unit that uses the operational amplifier class, reduce design difficulty and circuit power consumption, Fig. 2 has provided a kind of current sampling circuit of common no amplifier structure.This circuit uses current-mirror structure to replace amplifier, utilizes the complete symmetry characteristic of current-mirror structure, the drain terminal voltage of accurate replica current efferent duct MP1, thus realize the precise current sampling.The advantage on the current sample point road that Fig. 2 provides is, owing to do not use operational amplifier, circuit structure is simple, and design realizes that difficulty is little, simultaneously because the 3 grades of transistors of at most only connecting between power supply and the ground make the operating voltage of this circuit further to reduce.But the weak point of this circuit also is apparent in view.At first equation (1) (2) is still set up for this circuit, so sampling precision is subject to the size of tube of current output current equally; In addition, because the control that sampling main body circuit is received the current switch signal, therefore in each sampling period, the main body circuit all will experience once from the process by the end of unlatching, and this will introduce more noise and error undoubtedly, and limit the response performance of circuit greatly.
Summary of the invention
In order to reduce the operating voltage of sample circuit, avoid employing to the complicated sensitive circuit of operational amplifier class, and improve the sampling precision and the speed of circuit, the present invention proposes the structure of new current sampling circuit in conjunction with the advantage of the sample circuit of the described Fig. 1 of preamble and Fig. 2.
The basic point of departure of precise current sampling just is to duplicate accurately leakage, the source of the tube of current that is sampled, the current potential of grid in the sampling period, and passing ratio duplicates and forms sample rate current output.In order to realize this design object, need to solve several like this problems:
1. tube of current is formed scaled mirror;
2. in order to realize enough sampling response speeds, must keep the element task state of sample circuit, avoid occurring the switching of frequent ending-unlatching, therefore need the basic operating bias of design;
3. because the existence of basic biasing in order to compensate the influence of this biasing for sampling precision, must provide the bias compensation of special use, promptly eliminate second of the polynomial expression of equation (1);
4. for fear of using the complex calculations amplifier, utilize the form of current mirror and tail current source to constitute the voltage-tracing circuit, realize that current potential duplicates.
Concrete circuit structure as shown in Figure 3.
Tube of current MP1 is the target of current sample, needs in proportion replication stream through the electric current of MP1 pipe, the MP1 pipe by drain terminal to the external loading output current.Transistor MS1 is the sampling switch that is attempted by on the MP1 pipe, because the size of MP1 pipe is bigger, and the MS1 pipe is operated on off state, so the drain-source voltage of MS1 pipe is less, can ignore.The main effect of this structure is to obtain by the MS1 pipe drain terminal current potential of tube of current MP1.
Because sample enable signal Q is low in the sampling period, so MP2 manages and tube of current MP1 constitutes the current mirror relation, and the current replication ratio is 1/M, and because MP3 and MP2 manage the holosymmetric equal proportion current mirror relation of formation, so electric current I 2 equates with I3.And because automatic biasing current mirror that MP4 and MP5 pipe constitute and the existence of tail current limiting tube MN3 and MN4, the current potential that VA and VB are ordered equates.And because the automatic biasing current mirror that MP4 and MP5 pipe constitutes has strict proportionate relationship, so the part of having only size to equal bias current Ib in the electric current I 2 flows through current mirror MP4, equally also has only the electric current of Ib size to flow through current mirror MP5.Simultaneously because the existence of compensating current element IS2, make Isense electric current strictness equal the to flow through 1/M of electric current of tube of current MP1.
Basic offset generating circuit by current source IS1 and mirror image pipe MN2 constitute produces the bias current that size equals Ib, and is mirrored to the main body circuit by MN3 pipe and MN4 pipe.And, wherein having comprised the Ib part that produces by biasing equally because the electric current I 3 that mirror image produces equals I2, therefore size of current is set specially, and to equal Ib current source IS2 in parallel with the MP3 pipe, compensates the sampling error of being brought by biasing circuit.
According to top analysis, can obtain such equation:
I
L＝I
1+I
MS1 (4)
I
2＝I
b+I
MS1＝I
3＝I
sense (5)
The expression formula that can be got sampling precision by equation (3) (4) (5) is:
Because sample rate current and bias current all much smaller than the output current of tube of current, can make that bias current Ib is less by special design in addition, thereby can ignore in the equation (6) second fully, so sampling precision approaches field planting.
Advantage of the present invention is:
1. utilize symmetrical fully current-mirror structure to guarantee that the current potential that VA and VB are ordered accurately duplicates, avoided introducing the design complexities that operational amplifier brings.
2. utilize special bias current to make the sampling body current keep duty, avoid because of current mirror at the current over pulse that in opening transfer process, brings, improved response speed, reduced sampling error.
Specialized designs the error compensation electric current, in parallel with current mirror, offset the sampling error item that brings by fixed bias in the sampled result, improved sampling precision.
4. reduced transistorized piling up, the 3 layers of transistor of connecting at most between power supply and the ground make circuit to work under lower supply voltage.
Description of drawings
The current sampling circuit of the existing employing operational amplifier of Fig. 1 structure;
The low-voltage current sample circuit of the existing no amplifier structure of Fig. 2;
The current sampling circuit of the no amplifier structure of Fig. 3 suitable low voltage power supply disclosed by the invention;
The sampling precision curve of Fig. 4 current sampling circuit disclosed by the invention when different size of current;
The sampling precision curve of Fig. 5 current sampling circuit disclosed by the invention when different temperatures.
Embodiment
Below in conjunction with accompanying drawing, describe the structure and the course of work of current sampling circuit of the no amplifier structure of suitable low voltage power supply disclosed by the invention in detail.
Figure 3 shows that the current sampling circuit of the no amplifier structure of suitable low voltage power supply disclosed by the invention.
Body current is made up of the current-mirror structure of cascade, the tail current path that MN3 pipe and MN4 pipe constitute, and source ground, the grid parallel connection is connected to the grid and the drain electrode of MN2 pipe in the basic biasing circuit simultaneously, and mirror image comes from the electric current of MN2 pipe in the biasing circuit; MP4 pipe and MP5 pipe constitute auto bias circuit, and the formation current-mirror structure, wherein the grid of MP4 pipe, leakage level link to each other, and are connected to the drain electrode of the grid and the tail current pipe MN3 of MP5 pipe, the drain electrode of MP5 pipe connects the drain electrode of MN4 pipe, and is connected to the grid of MR pipe in output current-voltage conversion circuit; MP3 and MP2 pipe constitute full symmetrical configuration, and mirror image is from the electric current of tube of current MP1, wherein the source electrode of MP2 pipe meets power vd D, grounded-grid, drain electrode connects the source electrode of MP4 pipe and the drain electrode of sampling switch pipe MS1, the source electrode of MP3 pipe meets power vd D, grounded-grid, and drain electrode connects the source electrode of MP5 pipe and outputs to the drain electrode of MR pipe in the current-voltage conversion circuit; MR pipe and sensitive resistance R constitute current-voltage conversion circuit, wherein the source electrode of MR pipe connects the drain electrode of tube of current MP3, grid connects the drain electrode of tail current pipe MN4, source electrode connecting resistance R and as the output of final sampled voltage, the other end ground connection of resistance R, the drain electrode of MR pipe is also connected to the output of fixed bias compensating circuit; The fixed bias compensating circuit is made of current source IS2, and current source is in parallel with the MP3 pipe, and its input meets power vd D, and output connects the drain electrode of MP3 pipe; Basic biasing circuit is made of current source IS1 and tube of current MN2 series connection, and wherein the input of current source IS1 meets power vd D, and its output connects the drain and gate of tube of current MN2, and is connected to the grid of MN3 pipe and MN4 pipe, the source ground of MN2 pipe; Sampling switch is made of the switching tube MS1 that is connected on the tube of current MP1, wherein tube of current MP1 is as the tube of current that is sampled, its source electrode meets power vd D, grid links to each other with the grid of switching tube MS1 and accepts the control of switching signal Q, the drain electrode of MP1 connects external loading and is connected to the source electrode of switching tube MS1, and the drain electrode of MS1 is connected to the drain electrode of tube of current MP2; External loading is made up of energy storage inductor L, filter capacitor C, actual loading RL and continued flow tube MN1, wherein an end of inductance L is connected to the drain electrode of tube of current MP1 and the drain electrode of continued flow tube MN1, the other end is connected to the end of filter capacitor C and a section of actual loading RL, filter capacitor C and actual loading RL parallel connection, other end ground connection, the source ground of continued flow tube MN1, grid meet switch controlling signal Q.
Outside the sampling period, sampling switch Q is a noble potential, and Q is an electronegative potential, and tube of current MP1 ends, and does not provide electric current to external loading, external loading constitute the loop by energy storage inductor L and continued flow tube MN1, and keep working current.At this moment, because MP2, MP3 and MP1 do not constitute mirror, so the main body circuit relies on basic bias current Ib to keep work, because MP2 and MP3 are symmetries fully, relational expression arranged at this moment:
I
2＝I
3＝I
b (7)
The bias potential that provided by MN4 this moment makes the MR pipe open, because the existence of bias compensation circuit IS2, therefore the electric current that flows through on the sampling resistor R is Ib, so sampling and outputting voltage is:
V
sense＝I
b×R (8)
In the sampling period, sampling switch Q is an electronegative potential, and Q is a noble potential, opens tube of current MP1 to the external loading output current, and continued flow tube MN1 ends, and sampling switch MS1 pipe is opened simultaneously.Because MS1 pipe size is less, and works in the saturation region, so the drain-source voltage of MS1 falls and can ignore.This moment, the MP2/MP3 pipe constituted current mirror with tube of current MP1, because the existence of automatic biasing current mirroring circuit MP4 and MP5 and tail current pipe MN3 and MN4, at VA and VB point, can only distinguish left and outflow to the right by the electric current that the MP2/MP3 mirror image produces, the part that flows out imports load current to the right, because this part electric current is the microampere rank, influence to load current can be ignored, and the electric current that flows out left is through after the fixed bias compensation, form accurate replica current and flow through sensitive resistance R, form sampled voltage output.The bias potential that is provided by the MN4 pipe has guaranteed the smooth unlatching of MR pipe.
Because the MP2/MP3 pipe is of a size of the 1/M of MP1, so equation (3) is set up.In addition, can obtain equation (4) and (5) by Kirchhoff's current law (KCL).The process simple transformation can obtain the sampling error of current sampling circuit disclosed by the invention, represents as equation (6).
In equation (6),, therefore can keep quite high sampling precision because Isense and Ib are other Weak current of microampere order.Fig. 4 and Fig. 5 have provided the sampling precision curve of current sampling circuit disclosed by the invention under different output current and different temperatures respectively, and visible this circuit has a very high sampling precision among the figure.
Claims (1)
1. circuit structure comprises:
Demand at high-precision current sampling in the low voltage power supply system, utilize the accurate replication capacity of electric current of current mirror, the leakage of device will be sampled, the source, the current potential of grid accurately copies on the sampling pipe, the ratio-voltage of electric current to be measured is picked up in the pressure drop that the passing ratio electric current produces on fixed resistance, the sampling of realization precise current, it is characterized in that: sampling switch is made of the switching tube MS1 that is articulated on the tube of current MP1, the source electrode of tube of current MP1 meets power vd D, the source electrode of drain electrode link switching tube MS1, and be connected to external loading, the grid of switching tube MS1 connects the grid of tube of current MP1, and accepts the control of switching signal Q; External loading is made up of inductance L, continued flow tube MN1, capacitor C and actual loading RL, the source ground of continued flow tube MN1 wherein, and grid connects control signal
, drain electrode connects the electric current input of tube of current MP1, and is connected to an end of inductance L, and the other end of inductance connects an end of capacitor C and the input end of actual loading RL, the other end ground connection of capacitor C and actual loading RL; Basic biasing circuit is made up of current source IS1 and tube of current MN2, the input termination power of current source IS1, and output terminal links to each other with the drain and gate of tube of current MN2, the source ground of tube of current MN2, the grid of tube of current MN2 is as the output of basic bias potential; The main body circuit structure is by tail current limliting offset MN3 and MN4, full mirror-image structure MP4 and MP5, current sample pipe MP2 and MP3 form, wherein MN3 and MN4 respectively with basic biasing circuit in MN2 pipe constitute current mirror, the source ground of MN3 pipe, grid connects the grid of MN2 pipe and the grid of MN4 pipe, drain electrode connects the grid of MP4, the grid of drain electrode and MP5, the source ground of MN4 pipe, drain electrode connects the drain electrode of MP5, the source electrode of current sample pipe MP2 meets power vd D, grounded-grid, the drain electrode of source electrode and the current switch pipe MS1 of MP4 is received in drain electrode, the source electrode of current sample pipe MP3 meets power vd D, grounded-grid, the source electrode of MP5 is received in drain electrode, and as the output of sample rate current; The fixed bias compensation is made of current source IS2, and its input meets power vd D, and output connects the sample rate current output of main body circuit and the input of current-voltage sampling output circuit; Current-voltage sampling output circuit is made up of load pipe MR and sampling resistor R, wherein the drain electrode of load pipe MR connects the sample rate current output of main body circuit, grid connects the drain electrode of MP5, and source electrode meets sampling resistor R and exports the other end ground connection of sampling resistor R as final sampled voltage.
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|---|---|---|---|
| CN2009100436414A CN101629973B (en) | 2009-06-09 | 2009-06-09 | High-precision current sampling circuit without operational amplifier for low voltage power supply |
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|---|---|---|---|
| CN2009100436414A CN101629973B (en) | 2009-06-09 | 2009-06-09 | High-precision current sampling circuit without operational amplifier for low voltage power supply |
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| CN101629973B true CN101629973B (en) | 2011-04-20 |
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