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Renesas Electronics and Hitachi Develop High-Speed Converter Circuit

RenesasRenesas Electronics Corporation and Hitachi have recently announced a technology collaboration to enable continuous-time digital calibration of a delta-sigma (ΔΣ) modulator and an analog-to-digital (A/D) converter circuit.

Designed to boost the performance of ΔΣ A/D converters for stable performance under the harsh conditions required for automotive semiconductor devices, the new technology comprises (1) enhanced precision by using a least mean square (LMS) algorithm to measure and calibrate the transfer function of a continuous-time ΔΣ modulator, and (2) the world’s first multi-rate LMS search algorithm, which lowers the order and operating frequency of the coefficient search circuit and FIR digital filter to reduce power consumption. The 28 nm process was used to implement a multi-stage ΔΣ A/D converter employing sequential integrators operating at high speed.

Previously, digital calibration circuits were required to operate at an oversampling frequency of A/D converters, but the new circuit reduces the operating frequency to one-fourth the previous frequency. As a result, high-speed, high-precision operation with a signal bandwidth of 15 MHz and dynamic range of 74.3 dB is achieved when operating at an oversampling frequency of 480MHz.

By reducing the digital calibration circuit operating frequency to 120MHz, low-power operation is also achieved, with 37mW power consumption (analog:19mW, digital:18mW). In addition, the new technology has been confirmed to provide stable performance over a wide temperature range, proving that it is highly robust and capable of stable operation under punishing conditions.

The results of this joint effort with Hitachi were presented by Renesas on February 18 at the International Solid-State Circuits Conference (ISSCC) 2020.

In recent years, as advanced driver assistance systems (ADAS) and self-driving vehicles come closer to becoming a reality, there has been an increasing need for automobiles to incorporate a variety of sensors, such as millimeter wave radar, LiDAR, and ultrasonic wave sensors, in order to detect objects and people, and to provide an awareness of the vehicle’s surroundings. A/D converters used to convert analog signals from such sensors into digital signals must operate at a high speed and with high precision.

However, the harsh conditions specific to automotive vehicles have made obtaining stable performance an important issue. In response, Renesas and Hitachi developed the new continuous-time digital calibration technology to make high-speed, high-precision ΔΣ A/D converters capable of withstanding punishing conditions a reality. The new A/D converter circuit technology developed jointly by Renesas and Hitachi is described below.

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Nitisha Dubey

I am a Journalist with a post graduate degree in Journalism & Mass Communication. I love reading non-fiction books, exploring different destinations and varieties of cuisines. Biographies and historical movies are few favourites.

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