A Sigma-Delta ADC for Signal Conditioning IC of Automotive Piezo-Resistive Pressure Sensors with over 80 dB SNR

Abstract

This paper presents a second-order discrete-time Sigma-Delta (SD) Analog-to-Digital Converter (ADC) with over 80 dB Signal to Noise Ratio (SNR), which is applied in a signal conditioning IC for automotive piezo-resistive pressure sensors. To reduce the flicker noise of the structure, choppers are used in every stage of the high gain amplifiers. Besides, to reduce the required area and power, only the CIC filter structure is adopted as a decimation filter. This filter has a configurable structure that can be applied to different data rates and input signal bandwidths. The proposed ADC was fabricated and measured in a 0.18-µm CMOS process. Due to the application of only a CIC filter, the total active area of the SD-ADC and reference generator is 0.49 mm2 where the area of the decimation filter is only 0.075 mm2. For the input signal bandwidth of 1.22 kHz, it achieved over 80 dB SNR in a 2.5 MHz sampling frequency while consuming 646 µW power.

Keywords

• Sigma-Delta ADC
• flicker noise
• pressure sensor
• chopper
• decimation filter