CN101629973B - High-precision current sampling circuit without operational amplifier for low voltage power supply - Google Patents

电流采样电路广泛应用于各种以电流为媒介的集成电路之中，随着集成电路工艺水平的不断提高，供电电压不断下降，传统的电流采样结构已经不再适用于低电压供电的集成电路类应用。本发明公开了一种用于开关电源控制回路的高精度电流采样电路，利用电流镜结构代替了运算放大器，简化了电路结构，利用微安级的固定偏置提高了电流采样电路的响应速度，并对由固定偏置引入的采样误差进行了主动修正，提高了采样精度。电路由主体结构、基本偏置、电流-电压采样输出、固定偏置补偿、电流管与采样开关和外部负载六个部分组成。

Current sampling circuits are widely used in various integrated circuits that use current as the medium. With the continuous improvement of integrated circuit technology, the supply voltage continues to drop, and the traditional current sampling structure is no longer suitable for low-voltage power supply integrated circuits. application. The invention discloses a high-precision current sampling circuit for a switching power supply control loop, which uses a current mirror structure instead of an operational amplifier, simplifies the circuit structure, and improves the response speed of the current sampling circuit by using a microampere-level fixed bias. And the sampling error introduced by the fixed offset is actively corrected to improve the sampling accuracy. The circuit consists of six parts: main structure, basic bias, current-voltage sampling output, fixed bias compensation, current tube and sampling switch, and external load.

适用于低电压供电的无运放高精度电流采样电路 High-precision current sampling circuit without operational amplifier for low-voltage power supply

技术领域technical field

本发明属于集成电路设计领域，用于对通过晶体管的电流进行精确采样，具体涉及一种适合低电压供电场合的、不需要运算放大器、结构简单的高精度电流采样电路。The invention belongs to the field of integrated circuit design and is used for accurately sampling the current passing through a transistor, in particular to a high-precision current sampling circuit suitable for low-voltage power supply occasions, which does not require an operational amplifier and has a simple structure.

背景技术Background technique

电流采样技术是电流模式控制环路和电流保护电路中的关键技术，在利用电流形成闭环控制的集成电路中，电流采样是必不可少的电路组成部分，尤其是在电流反馈控制的开关电源类集成电路中，电流采样电路的性能直接关系到电路整体的性能。Current sampling technology is the key technology in current mode control loop and current protection circuit. In integrated circuits that use current to form closed-loop control, current sampling is an essential circuit component, especially in switching power supplies that are controlled by current feedback. In an integrated circuit, the performance of the current sampling circuit is directly related to the overall performance of the circuit.

电流采样的方法中最常见的是在被采样电流通路上直接串联一个小阻值的采样电阻，从电阻的压降得到通过被采样的电流管的电流。这种方法简单易行，但是采样电阻串联在主电流通路商，会消耗大量的功率，降低整个芯片的工作效率，并且随着输出电压的降低，采样电阻所消耗的功率在整个芯片中的功耗中的比重会进一步加大。The most common method of current sampling is to directly connect a small-value sampling resistor in series with the sampled current path, and obtain the current passing through the sampled current tube from the voltage drop of the resistor. This method is simple and easy to implement, but the sampling resistor is connected in series with the main current path, which will consume a lot of power and reduce the working efficiency of the entire chip. The proportion of consumption will further increase.

为了避免采样电阻对电流输出通路的影响，通常采用电位复制的方法。图1中是一种采用运放结构的电流采样方法，这种方法利用运算放大器输入端“虚短”的特性，将被采样电流管MP1的漏端电压“复制”到采样管MP2的漏端，由于构成电流镜的采样管MP2与被采样电流管MP1的沟道长度相同，宽度成比例缩小，因此MP2可以精确的按比例镜像流过电流管MP1的电流，从而实现电流采样。不妨假设MP1与MP2管的宽度比例为M，基本偏置电流为Ib，电路对负载的输出电流为IL，采样得到的感应电流为Isense，那么根据由MP1和MP2构成的电流镜的比例关系可以得到等式(1)。In order to avoid the impact of the sampling resistor on the current output path, the method of potential replication is usually used. Figure 1 is a current sampling method using an operational amplifier structure. This method uses the "virtual short" characteristic of the input terminal of the operational amplifier to "copy" the drain terminal voltage of the sampled current tube MP1 to the drain terminal of the sampling tube MP2. , because the channel length of the sampling tube MP2 constituting the current mirror is the same as that of the sampled current tube MP1, and the width is proportionally reduced, so MP2 can accurately mirror the current flowing through the current tube MP1 in proportion to realize current sampling. It may be assumed that the width ratio of MP1 and MP2 is M, the basic bias current is Ib, the output current of the circuit to the load is IL, and the induced current obtained by sampling is Isense, then according to the proportional relationship of the current mirror formed by MP1 and MP2, it can be Equation (1) is obtained.

I_L＝M×I_sense+(M-1)×I_b                            (1)I _L ＝M×I _sense +(M-1)×I _b (1)

等式(1)中多项式的第一项为理想的比例电流采样关系，第二项为采样误差，因此该电路的电流采样精度为等式(2)。可见该电路存在固有的采样误差，并且这个误差随着电流管输出电流的减小而不断增大。此外，由于运算放大器的存在，加大了电路设计的难度，运算放大器的增益和响应速度直接关系到整体采样的精度和响应速度。并且，在该电路中，从电源到地，最多存在4级串联的晶体管，这就使得该电路不可能工作电源电压较低的电路中。The first term of the polynomial in Equation (1) is the ideal proportional current sampling relationship, and the second term is the sampling error, so the current sampling accuracy of this circuit is Equation (2). It can be seen that there is an inherent sampling error in this circuit, and this error increases continuously with the decrease of the output current of the current tube. In addition, due to the existence of the operational amplifier, the difficulty of circuit design is increased, and the gain and response speed of the operational amplifier are directly related to the accuracy and response speed of the overall sampling. Moreover, in this circuit, there are at most 4 stages of transistors connected in series from the power supply to the ground, which makes it impossible for the circuit to work in a circuit with a lower power supply voltage.

ηη == (( Mm -- 11 )) ×× II bb II LL ×× 100100 %% -- -- -- (( 22 ))

为了避免使用运算放大器类的敏感部件，降低设计难度和电路功耗，图2给出了一种常见的无运放结构的电流采样电路。该电路使用电流镜结构取代了运放，利用电流镜结构的完全对称特性，精确复制电流输出管MP1的漏端电压，从而实现精确的电流采样。图2给出的电流采样点路的优点在于，由于不使用运算放大器，电路结构简单，设计实现难度小，同时由于电源与地之间最多只串联3级晶体管，使得该电路的工作电压能够进一步降低。但是，该电路的不足之处也是比较明显的。首先等式(1)(2)对于该电路仍然成立，因此采样精度同样受限于电流管输出电流的大小；此外，由于采样主体电路收电流开关信号的控制，因此在每个采样周期内，主体电路都将经历一次从截止到开启的过程，这无疑将引入更多的噪声和误差，并大大限制了电路的响应性能。In order to avoid the use of sensitive components such as operational amplifiers and reduce design difficulty and circuit power consumption, Figure 2 shows a common current sampling circuit without an operational amplifier structure. The circuit uses a current mirror structure instead of an operational amplifier, and uses the complete symmetry of the current mirror structure to accurately replicate the drain voltage of the current output transistor MP1, thereby realizing accurate current sampling. The advantage of the current sampling point circuit shown in Figure 2 is that since no operational amplifier is used, the circuit structure is simple, and the design and implementation difficulty is small. reduce. However, the disadvantages of this circuit are also obvious. First of all, equations (1) and (2) are still valid for this circuit, so the sampling accuracy is also limited by the output current of the current tube; in addition, due to the control of the current switching signal of the sampling main circuit, in each sampling period, The main circuit will go through a process from cut-off to turn-on, which will undoubtedly introduce more noise and errors, and greatly limit the response performance of the circuit.

发明内容Contents of the invention

为了降低采样电路的工作电压，避免对运算放大器类复杂敏感电路的采用，并且提高电路的采样精度和速度，本发明结合前文所述图1和图2的采样电路的优点，提出新的电流采样电路的结构。In order to reduce the operating voltage of the sampling circuit, avoid the use of complex and sensitive circuits such as operational amplifiers, and improve the sampling accuracy and speed of the circuit, the present invention combines the advantages of the sampling circuits in Figure 1 and Figure 2 mentioned above to propose a new current sampling The structure of the circuit.

精确的电流采样的基本出发点，就在于能够在采样周期内精确的复制被采样的电流管的漏、源、栅的电位，并通过比例复制形成采样电流输出。为了实现这个设计目标，需要解决这样几个问题：The basic starting point of accurate current sampling is to be able to accurately replicate the potential of the drain, source, and gate of the current tube being sampled within the sampling period, and to form a sampled current output through proportional replication. In order to achieve this design goal, several problems need to be solved:

1.对电流管形成比例镜像；1. Form a proportional mirror image for the current tube;

2.为了实现足够的采样响应速度，必须保持采样电路的基础工作状态，避免出现频繁的截止-开启的切换，因此需要设计基本的工作偏置；2. In order to achieve sufficient sampling response speed, the basic working state of the sampling circuit must be maintained to avoid frequent cut-off-on switching, so it is necessary to design a basic working bias;

3.由于基本偏置的存在，为了补偿该偏置对于采样精度的影响，必须提供专用的偏置补偿，即消除等式(1)的多项式第二项；3. Due to the existence of the basic offset, in order to compensate the impact of the offset on the sampling accuracy, a dedicated offset compensation must be provided, that is, to eliminate the second term of the polynomial in equation (1);

4.为了避免使用复杂的运算放大器，利用电流镜与尾电流源的形式构成电压跟踪电路，实现电位复制。4. In order to avoid the use of complex operational amplifiers, a voltage tracking circuit is formed in the form of a current mirror and a tail current source to realize potential replication.

具体的电路结构如图3所示。The specific circuit structure is shown in Fig. 3 .

电流管MP1为电流采样的目标，需要按比例复制流经MP1管的电流，MP1管通过漏端对外部负载输出电流。晶体管MS1为并接在MP1管上的采样开关，由于MP1管的尺寸较大，并且MS1管工作在开关状态，因此MS1管的漏源电压较小，可以忽略。这个结构的主要作用在于通过MS1管取得电流管MP1的漏端电位。The current tube MP1 is the target of current sampling, and the current flowing through the MP1 tube needs to be copied in proportion, and the MP1 tube outputs current to the external load through the drain terminal. The transistor MS1 is a sampling switch connected in parallel to the MP1 tube. Since the size of the MP1 tube is large, and the MS1 tube works in a switching state, the drain-source voltage of the MS1 tube is small and can be ignored. The main function of this structure is to obtain the drain terminal potential of the current tube MP1 through the MS1 tube.

由于在采样周期内采样使能信号Q为低，因此MP2管与电流管MP1构成电流镜关系，电流复制比例为1/M，而由于MP3和MP2管构成全对称的等比例电流镜关系，因此电流I2和I3相等。并且由于MP4和MP5管构成的自偏置电流镜和尾限流管MN3和MN4的存在，VA和VB点的电位相等。而由于MP4和MP5管构成的自偏置电流镜具有严格的比例关系，因此电流I2中只有大小等于偏置电流Ib的部分流过电流镜MP4，同样也只有Ib大小的电流流过电流镜MP5。同时由于补偿电流源IS2的存在，使得Isense电流严格等于流经电流管MP1的电流的1/M。Since the sampling enable signal Q is low during the sampling period, the MP2 tube and the current tube MP1 form a current mirror relationship, and the current replication ratio is 1/M, and because the MP3 and MP2 tubes form a fully symmetrical equal-proportion current mirror relationship, so Currents I2 and I3 are equal. And because of the self-bias current mirror formed by MP4 and MP5 tubes and the existence of tail current limiting tubes MN3 and MN4, the potentials of VA and VB points are equal. Since the self-bias current mirror formed by MP4 and MP5 has a strict proportional relationship, only the part of the current I2 equal to the bias current Ib flows through the current mirror MP4, and only the current of Ib flows through the current mirror MP5. . At the same time, due to the existence of the compensation current source IS2, the Isense current is strictly equal to 1/M of the current flowing through the current tube MP1.

由电流源IS1和镜像管MN2构成的基本偏置产生电路，产生大小等于Ib的偏置电流，并通过MN3管和MN4管镜像到主体电路。而由于镜像产生的电流I3等于I2，其中同样包含了由偏置产生的Ib部分，因此专门设置电流大小等于Ib电流源IS2与MP3管并联，补偿由偏置电路带来的采样误差。The basic bias generating circuit composed of the current source IS1 and the mirror tube MN2 generates a bias current equal to Ib, and mirrors it to the main circuit through the MN3 tube and the MN4 tube. Since the current I3 generated by the mirror image is equal to I2, which also includes the Ib part generated by the bias, the current size is specially set to be equal to Ib. The current source IS2 is connected in parallel with the MP3 tube to compensate the sampling error caused by the bias circuit.

根据上面的分析，可以得到这样的等式：According to the above analysis, the following equation can be obtained:

II 33 == II 22 == 11 Mm ×× II 11 -- -- -- (( 33 ))

I_L＝I₁+I_MS1                                (4)I _L =I ₁ +I _MS1 (4)

I₂＝I_b+I_MS1＝I₃＝I_sense                    (5)I ₂ ＝I _b +I _MS1 ＝I ₃ ＝I _sense (5)

由等式(3)(4)(5)可得采样精度的表达式为：The expression of sampling accuracy obtained from equations (3)(4)(5) is:

ηη == II sensesense -- II bb II LL ×× 100100 %% -- -- -- (( 66 ))

由于采样电流和偏置电流均远小于电流管的输出电流，此外还可以通过专门的设计，使得偏置电流Ib较小，从而完全可以忽略等式(6)中的第二项，因此采样精度接近于定植。Since both the sampling current and the bias current are much smaller than the output current of the current tube, in addition, the bias current Ib can be made smaller through a special design, so that the second term in equation (6) can be completely ignored, so the sampling accuracy close to colonization.

本发明的优势在于：The advantages of the present invention are:

1.利用完全对称的电流镜结构保证了VA和VB点的电位精确复制，避免了引入运算放大器带来的设计复杂度。1. The use of a fully symmetrical current mirror structure ensures accurate replication of the potentials of VA and VB points, avoiding the design complexity brought by the introduction of operational amplifiers.

2.利用专门的偏置电流使得采样主体电流保持工作状态，避免因电流镜在截止到开启转换过程中带来的电流过冲，提高了响应速度，减小了采样误差。2. Use a special bias current to keep the current of the sampling main body in working state, avoid the current overshoot caused by the current mirror during the transition from cut-off to turn-on, improve the response speed, and reduce the sampling error.

3.专门设计了误差补偿电流，与电流镜并联，抵消了采样结果中由固定偏置带来的采样误差项，提高了采样精度。3. The error compensation current is specially designed and connected in parallel with the current mirror, which offsets the sampling error term caused by the fixed bias in the sampling result and improves the sampling accuracy.

4.减小了晶体管的堆叠，电源与地之间最多串联3层晶体管，使得电路能够在较低的供电电压下工作。4. The stacking of transistors is reduced, and at most 3 layers of transistors are connected in series between the power supply and the ground, so that the circuit can work at a lower power supply voltage.

附图说明Description of drawings

图1已有的采用运算放大器结构的电流采样电路；Fig. 1 existing current sampling circuit adopting operational amplifier structure;

图2已有的无运放结构的低电压电流采样电路；Fig. 2 is an existing low-voltage current sampling circuit without an op-amp structure;

图3本发明公开的适合低电压供电的无运放结构的电流采样电路；Fig. 3 is a current sampling circuit without an operational amplifier structure suitable for low-voltage power supply disclosed by the present invention;

图4本发明公开的电流采样电路在不同电流大小时的采样精度曲线；Fig. 4 is the sampling accuracy curve of the current sampling circuit disclosed by the present invention at different current sizes;

图5本发明公开的电流采样电路在不同温度时的采样精度曲线。Fig. 5 is the sampling accuracy curve of the current sampling circuit disclosed in the present invention at different temperatures.

具体实施方式Detailed ways

以下结合附图，详细说明本发明公开的适合低电压供电的无运放结构的电流采样电路的结构和工作过程。The structure and working process of the current sampling circuit with no operational amplifier structure suitable for low-voltage power supply disclosed by the present invention will be described in detail below in conjunction with the accompanying drawings.

图3所示为本发明公开的适合低电压供电的无运放结构的电流采样电路。FIG. 3 shows a current sampling circuit without an op-amp structure suitable for low-voltage power supply disclosed by the present invention.

主体电流由级联的电流镜结构组成，MN3管和MN4管构成的尾电流通路，源极接地，栅极并联，同时连接到基本偏置电路中MN2管的栅极和漏极，镜像来自于偏置电路中MN2管的电流；MP4管和MP5管构成自偏置电路，并形成电流镜结构，其中MP4管的栅、漏级相连，并连接到到MP5管的栅极和尾电流管MN3的漏极，MP5管的漏极连接MN4管的漏极，并连接到输出电流-电压转换电路中MR管的栅极；MP3和MP2管构成全对称结构，并镜像来自电流管MP1的电流，其中MP2管的源极接电源VDD，栅极接地，漏极连接MP4管的源极以及采样开关管MS1的漏极，MP3管的源极接电源VDD，栅极接地，漏极连接MP5管的源极并输出到电流-电压转换电路中MR管的漏极；MR管和敏感电阻R构成电流-电压转换电路，其中MR管的源极连接电流管MP3的漏极，栅极连接尾电流管MN4的漏极，源极接电阻R并作为最终的采样电压输出，电阻R的另一端接地，MR管的漏极还连接到固定偏置补偿电路的输出；固定偏置补偿电路由电流源IS2构成，电流源与MP3管并联，其输入接电源VDD，输出连接MP3管的漏极；基本偏置电路由电流源IS1和电流管MN2串联构成，其中电流源IS1的输入接电源VDD，其输出连接电流管MN2的漏极和栅极，并连接到MN3管和MN4管的栅极，MN2管的源极接地；采样开关由串联在电流管MP1上的开关管MS1构成，其中电流管MP1作为被采样的电流管，其源极接电源VDD，栅极与开关管MS1的栅极相连并接受开关信号Q的控制，MP1的漏极连接外部负载并连接到开关管MS1的源极，MS1的漏极连接到电流管MP2的漏极；外部负载由储能电感L、滤波电容C、实际负载RL和续流管MN1组成，其中电感L的一端连接到电流管MP1的漏极和续流管MN1的漏极，另一端连接到滤波电容C的一端和实际负载RL的一段，滤波电容C和实际负载RL并联，另一端接地，续流管MN1的源极接地，栅极接开关控制信号Q。The main current is composed of a cascaded current mirror structure, the tail current path formed by MN3 tube and MN4 tube, the source is grounded, the gate is connected in parallel, and connected to the gate and drain of the MN2 tube in the basic bias circuit at the same time, the mirror image comes from The current of the MN2 tube in the bias circuit; the MP4 tube and the MP5 tube form a self-bias circuit and form a current mirror structure, where the gate and drain of the MP4 tube are connected, and connected to the grid of the MP5 tube and the tail current tube MN3 The drain of the MP5 tube is connected to the drain of the MN4 tube and connected to the gate of the MR tube in the output current-voltage conversion circuit; the MP3 and MP2 tubes form a fully symmetrical structure and mirror the current from the current tube MP1, The source of the MP2 tube is connected to the power supply VDD, the gate is grounded, the drain is connected to the source of the MP4 tube and the drain of the sampling switch MS1, the source of the MP3 tube is connected to the power supply VDD, the gate is grounded, and the drain is connected to the MP5 tube. The source is output to the drain of the MR tube in the current-voltage conversion circuit; the MR tube and the sensitive resistor R form a current-voltage conversion circuit, in which the source of the MR tube is connected to the drain of the current tube MP3, and the gate is connected to the tail current tube The drain and source of MN4 are connected to the resistor R and output as the final sampling voltage, the other end of the resistor R is grounded, and the drain of the MR tube is also connected to the output of the fixed bias compensation circuit; the fixed bias compensation circuit is composed of a current source IS2 Composition, the current source is connected in parallel with the MP3 tube, its input is connected to the power supply VDD, and the output is connected to the drain of the MP3 tube; the basic bias circuit is composed of the current source IS1 and the current tube MN2 connected in series, where the input of the current source IS1 is connected to the power supply VDD, and its output Connect the drain and gate of the current tube MN2, and connect to the gates of the MN3 tube and the MN4 tube, the source of the MN2 tube is grounded; the sampling switch is composed of a switch tube MS1 connected in series with the current tube MP1, and the current tube MP1 is used as The source of the sampled current tube is connected to the power supply VDD, the gate is connected to the gate of the switch tube MS1 and is controlled by the switch signal Q, the drain of MP1 is connected to an external load and connected to the source of the switch tube MS1, and the gate of MS1 The drain is connected to the drain of the current tube MP2; the external load is composed of the energy storage inductor L, the filter capacitor C, the actual load RL and the freewheeling tube MN1, wherein one end of the inductor L is connected to the drain of the current tube MP1 and the freewheeling tube The drain of MN1, the other end is connected to one end of the filter capacitor C and a section of the actual load RL, the filter capacitor C and the actual load RL are connected in parallel, the other end is grounded, the source of the freewheeling tube MN1 is grounded, and the gate is connected to the switch control signal Q .

在采样周期之外，采样开关Q为高电位，Q为低电位，电流管MP1截止，不对外部负载提供电流，外部负载的由储能电感L和续流管MN1构成回路，并维持工作电流。此时，由于MP2、MP3与MP1不构成镜像关系，因此主体电路依靠基本偏置电流Ib维持工作，由于MP2和MP3是完全对称的，此时有关系式：Outside the sampling period, the sampling switch Q is at high potential, Q is at low potential, the current tube MP1 is cut off, and no current is supplied to the external load. The external load is composed of the energy storage inductor L and the freewheeling tube MN1 to form a loop and maintain the working current. At this time, since MP2, MP3 and MP1 do not form a mirror image relationship, the main circuit relies on the basic bias current Ib to maintain work. Since MP2 and MP3 are completely symmetrical, there is a relationship at this time:

I₂＝I₃＝I_b                            (7)I ₂ =I ₃ =I _b (7)

此时由MN4提供的偏置电位使得MR管开启，由于偏置补偿电路IS2的存在，因此流过采样电阻R上的电流为Ib，因此采样输出电压为：At this time, the bias potential provided by MN4 makes the MR tube turn on. Due to the existence of the bias compensation circuit IS2, the current flowing through the sampling resistor R is Ib, so the sampling output voltage is:

V_sense＝I_b×R                         (8)V _sense =I _b ×R (8)

在采样周期内，采样开关Q为低电位，Q为高电位，打开电流管MP1对外部负载输出电流，续流管MN1截止，同时采样开关MS1管打开。由于MS1管尺寸较小，并且工作于饱和区，因此MS1的漏源电压降可以忽略。此时MP2/MP3管与电流管MP1构成电流镜，由于自偏置电流镜电路MP4和MP5以及尾电流管MN3和MN4的存在，在VA和VB点，由MP2/MP3镜像产生的电流只能分别向左和向右流出，向右流出的部分汇入负载电流，由于这部分电流为微安级别，对负载电流的影响可以忽略，而向左流出的电流经过固定偏置补偿之后，形成精确的复制电流流过敏感电阻R，形成采样电压输出。由MN4管提供的偏置电位保证了MR管的顺利开启。During the sampling period, the sampling switch Q is at low potential and Q is at high potential, the current tube MP1 is turned on to output current to the external load, the freewheeling tube MN1 is cut off, and the sampling switch MS1 is turned on at the same time. Since the MS1 tube is small in size and works in the saturation region, the drain-source voltage drop of MS1 can be ignored. At this time, the MP2/MP3 tube and the current tube MP1 form a current mirror. Due to the existence of the self-bias current mirror circuits MP4 and MP5 and the tail current tubes MN3 and MN4, at points VA and VB, the current generated by the mirror image of MP2/MP3 can only be Flow out to the left and right respectively, and the part that flows out to the right is absorbed into the load current. Since this part of the current is in the microampere level, the impact on the load current can be ignored, and the current that flows out to the left is formed after a fixed bias compensation. The replica current flows through the sensitive resistor R to form a sampled voltage output. The bias potential provided by the MN4 tube ensures the smooth opening of the MR tube.

由于MP2/MP3管的尺寸为MP1的1/M，因此等式(3)成立。此外，由基尔霍夫电流定律可以得到等式(4)和(5)。经过简单变换即可得到本发明公开的电流采样电路的采样误差，如等式(6)表示。Since the size of the MP2/MP3 pipe is 1/M of MP1, equation (3) holds. Furthermore, equations (4) and (5) can be obtained from Kirchhoff's current law. The sampling error of the current sampling circuit disclosed in the present invention can be obtained through simple transformation, as expressed by equation (6).

在等式(6)中，由于Isense和Ib均为微安级别的微小电流，因此可以保持相当高的采样精度。图4和图5分别给出了本发明公开的电流采样电路在不同输出电流和不同温度下的采样精度曲线，图中可见该电路的具有很高的采样精度。In equation (6), since both Isense and Ib are tiny currents of the microampere level, a fairly high sampling accuracy can be maintained. Fig. 4 and Fig. 5 respectively show the sampling precision curves of the current sampling circuit disclosed in the present invention under different output currents and different temperatures, and it can be seen from the figure that the circuit has very high sampling precision.

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.