Automatic shift current mirror

Abstract

The invention relates to a current mirror with automatic shift, composed of a current sensitive circuit serially connected with a current mirror with multistage adjustable magnification, wherein the circuit detects the input current of the current mirror at one stage to be compared with a preset convert point, when the compared result meets switch condition, the circuit outputs a switch signal to the current mirror of each stage to adjust the magnification of each stage, thereby improving bias current and improve the uniformity of output current.

Description

technical field [0001] The invention relates to a current mirror, in particular to a current mirror which can automatically switch bias current and magnification to reduce errors. Background technique [0002] For a conventional current mirror composed of MOS devices (Metal Oxide Semiconductor Field Effect Transistor), the accuracy between the bias current and the output current will vary with the bias current. [0003] The MOS components in the current mirror usually operate in the saturation region, and the MOS source current in the simple saturation region (I ds ) relative to the gate voltage (V gs ) can be expressed by the following equation: [0004] I ds =[μC ox (W / L)(V gs -V th ) 2 ] / 2 [0005] Due to the process relationship, for different MOS components, μ and C in the above formula ox , W, L, V th And other parameters are difficult to be exactly the same and there are some errors. In the same current mirror, μC ox (W / L) will not change much under differ...

AI Technical Summary

Problems solved by technology

However, the smaller the bias current, the larger the error still exists

[0007] In applications that require high current accuracy, the aforementioned error problem is very critical. For example, the LED / OLED drive circuit provides multiple output currents. Under low current operation, the error between the input current and the output current and the multi-channel output The current uniformity (skew) is obviously worse than that of high current operation, which also leads to the limitation of the adjustment range of the output current, because the maximum bias current has its upper limit according to the specifications of the MOS components. If the bias current is too much lower than the upper limit, It will lead to a rapid increase in the amount of error and cannot meet the needs of users, resulting in bottlenecks in research and development and application

Images