A High-Performance Audio ∑-△ Digital-to-Analog Converter

In 2006's "The development outline of long-term national science and technology (2006-2020)" which determines the next 15 years striving to achieve a major breakthrough in the 16 special science and technology programs,the first is the key electronic devices,high-end general chips and basic software.High performance Digital-to-analog converters(DAC) are just high-end general chips,which are very important for electronic products to gain market competitiveness.This paper focuses on audio digital-to-analog conversion technology.For high-resolution digital-to-analog conversion,oversampling∑-△is the best choice.∑-△digital-to-analog converter is composed of interpolation low-pass filter,digital∑-△modulator and analog back-end circuit.The technology demands fairly deep unstanding of digital IC design and analog IC design,so it is the most difficult system-level IC in all kinds of DACs.How to realize good linearity and low noise is crucial.Here a multi-bit quantizer∑-△DAC is proposed,which adopts direct current transfer technique to realize digital-to-analog conversion,reducing power consumption. Compared to single-bit internal DAC topology,the new circuit has the advantages of less analog part area and less power disspation.The chip is fabricated on SMIC 0.18μm process,with the core area of 1.86 mm2. The dynamic range is 96 dB,and the maximum signal-to-noise ratio is 88 dB.All the circuit modules reach the design specifications,proving feasibility of the design,and a high performance audio DAC is realized.The main work and innovation of the paper includes:1.With analysing the principle of∑-△modulator,a deep understanding of stability and topology is obtained.Besides,in order to save hardware resourse and reduce IC power,CSD code is chosen to implement multipliers in digital interpolation filter.2.With adopting multi-bit truncator in∑-△converter and direct-current-transfer SC DAC,power dissapation is reduced.Comparing to single-bit internal DAC,the topology has much advantage in chip area and power.3.It is hard to directly get high linearity with multi-bit switched-capacitor DAC.In the design,a mismatch error shaping algorithm is introduced to convert mismatch error in to noise and "push" it to high-frequency part,which is out of signal band, reducing noise greatly.4.A substrate noise active cancellation methode is proposed.Through simulation,it found the method can lower the substrate noise largely.This gives another choice for mixed-signal IC layout design.5.The test result is very good,with 96 dB dynamic range,and 88 dB signal-to-nosie ratio.Compared to test results of domestic audio DACs in recent years,the design has reached the leading level in China.The paper gives a deep research on∑-△DACs,and designs a high performance 18-bit DAC chip,which is comparable to foreign like products.Through the chip design,and a complete mixed-signal IC design procedure is verified,from system-level design,circuit design,and layout design,to test verification.And the most important of all is that we get the proprietary intellectual property right of a high performacne audio DAC chip.