A 2GHz On-Chip-Oscilloscope with High Accuracy Pulse Width Detection for Auto-Peak-Power Controller & Peak-Current Detector in Voltage-Mode DToF Driver

This paper presents a high-speed and high-resolution On-Chip Oscilloscope (OCO) for Auto-Peak-Power Controller (APPC) and Peak-Current Detector in voltage mode Direct Time-of-Flight(DToF) driver. The OCO supports both optical input and electrical input, with front-end circuit of TIA and PGA respectively. The front-end circuit bandwidth is up to 2GHz to support 500ps pulse width detection. The optical input is for detecting VCSEL peak power, and feedback to the integrated Boost Converter to adjust VCSEL supply voltage to find the target peak optical power. The electrical input is for detecting the VCSEL peak current to avoid driver over-current, by preventing APPC from adapting to excessive peak current due to abnormal VCSEL or PD. The front-end circuit is followed by an 11-bit asynchronous logic SAR-ADC with up to 40MHz sampling rate. The OSC time accuracy is 6.6ps and detected pulse width is up to 12.8ns. The chip was fabricated in BCD180nm process. According to the test results, the measured waveform of OCO is comparable with commercial oscilloscope. By turning on the OCO-based APPC feature, the variation of optical power is controlled within 3% in the temperature range of 25-85°C.