A constant current source generating circuit for a common-cathode LED display driver chip

Abstract

The invention discloses a constant-current source generation circuit of a common-cathode LED display screen driving chip. The constant-current source generation circuit comprises a reference current module, a bias generation circuit, a current control circuit and a constant-current source output circuit which are connected in sequence, the reference current module generates reference current or voltage and generates reference current through trimming; the bias generation circuit inputs reference current to generate bias voltage VD and VGI required by the constant current source output channel;the bias voltage VGI and a current control signal S [0:M] are input into the current control circuit, and bias voltage VGO [0: M] is output by the current control circuit; the bias voltages VD and VGO [0: M] and an enable signal OE are input into the constant-current source output circuit, and when the enable signal OE is effective, the constant-current source output circuit outputs constant output current IOUT; the invention aims to provide the constant-current source generating circuit of the common-cathode LED display screen driving chip, an external resistor of the chip is not needed, thepower consumption is low, and the system cost is saved; and while the area of the chip is reduced, constant-current output with higher precision is realized.

Description

technical field [0001] The invention relates to a constant current source generating circuit, in particular to a constant current source generating circuit for a common-cathode LED display drive chip. Background technique [0002] figure 1 It is a commonly used constant current source drive generation circuit in the common cathode LED display constant current source drive chip. R_EXT in the figure is the external resistance of the drive chip; figure 2 It is a flow chart of the existing constant current source generating method. [0003] The gain of all amplifiers in the figure is infinite, and the principle of constant current source generation is as follows: [0004] 1. Generate the required reference potential VREF1 from Bandgap; [0005] 2. The source potential of the NMOS transistor NM0 is clamped to VREF1 by the amplifier AMP1, so the source-leakage current flowing through the PMOS transistor PM0 is: I0=VREF1 / R_EXT; [0006] 3. C[0:L] is a voltage selection signal ...

AI Technical Summary

Problems solved by technology

[0017] 1. The area is large;

[0018] 2. It is difficult to improve the current accuracy, because the current accuracy is proportional to the arithmetic square root of the device area, and due to the production process, when the area increases to a certain amount, the accuracy will not always improve

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