An Adjustable Ramp Voltage Circuit for a Large Array of Capacitive Loads

In current image sensor circuits, the traditional ramp circuit shows the problems of low precision of adjustable slope and insufficient driving ability when facing a large array. This paper proposes a high-precision and high-driving adjustable ramp voltage circuit for the image sensor, including a bandgap reference voltage source, a current mirror array, and a buffer driver. The reference current in the proposed adjustable ramp circuit adopts a high-precision bandgap design, and a buffer driver circuit is added to ensure the slope accuracy. Meanwhile, the output terminal adopts a push-pull structure. Simulation results in a 65 nm CMOS process show that the proposed adjustable ramp generation circuit can drive a large array of capacitive loads with a ramp voltage range from 1 V to 5 V and an adjustable slope range from 6 $\mu$s to 60 $\mu$s. The adjustable ramp circuit can achieve 1-10 dynamic adjustments, and a large array of capacitive loads can be driven when dynamic adjustment is achieved. Compared with the traditional resistance or capacitance adjustable circuit, the slope accuracy increases by 20%, and the driving ability of the proposed adjustable ramp circuit increases by 61.35%.