Successive approximation type a/d converter circuit

Abstract

In an A / D converter circuit having a chopper comparator, only a small number of elements are additionally provided to impart a hysteresis characteristic to the comparator, thereby reducing the conversion errors caused by noise. In a successive approximation type A / D converter circuit having a chopper comparator, one or more amplifier stages are provided to the comparator circuit (CMP), and a feedback capacitor (Cf), which is connected to the input terminal of one of the amplifier stages, is also provided to the comparator circuit (CMP). In the A / D converter circuit, during a first interval, an input analog voltage is taken in, and during a second interval, a voltage, which is in accordance with a potential difference between the input analog voltage and the comparison voltage, is inputted and the input potential is amplified by the amplifier stages. When the output of the comparator circuit changes, a positive feedback is applied through the feedback capacitor to the input terminal of the corresponding amplifier stage, thereby providing a hysteresis of 1 LSB or less.

Description

technical field [0001] The present invention relates to a technique for imparting hysteresis characteristics to a comparator in a successive approximation type AD conversion circuit, and particularly relates to a technique suitable for use in an AD conversion circuit including a chopping type comparator. Background technique [0002] Portable electronic devices such as mobile phones, PDAs (Personal Digital Assistants), and digital cameras are equipped with microprocessors for controlling systems inside the devices, and the microprocessors monitor temperature and battery voltage for control. Therefore, in many cases, sensors for detecting temperature, battery voltage, and the like are provided in the device, and an A / D conversion circuit that converts analog signals from these sensors into digital signals is incorporated in the microprocessor. [0003] In addition, it is desired that an A / D conversion circuit built in a microprocessor or the like has a small circuit scale. A...

AI Technical Summary

Problems solved by technology

[0004] At present, in order to prevent malfunction caused by noise contained in the input signal, the comparator has a hysteresis characteristic.

However, in the A / D conversion circuit, if the comparator has a hysteresis characteristic, it becomes an AD conversion error, especially in an A / D conversion circuit with a large number of input bits (bit) or high resolution, due to the hysteresis The minimum resolution is embedded in the LSB (Least Significant Bit: Least Significant Bit), so it generally does not have hysteresis characteristics

[0005] On the other hand, the chopper-type comparator amplifies the potential difference between the input analog signal Vin and the comparison voltage Vref through the CMOS inverter, so when Vin becomes approximately equal to Vref, due to slight fluctuations in the input potential , causing the erratic action of switching the output to high / low

Furthermore, there is a problem that a current change occurs in the CMOS inverter at the time of this switching, which becomes power supply noise, swings the reference voltage of the comparator, and lowers the conversion accuracy.

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