Passive bandpass Delta-Sigma modulator based on time-interleaved SAR (Synthetic Aperture Radar) ADC (Analog-to-Digital Converter)

Abstract

The invention belongs to the technical field of integrated circuits, in particular to a passive bandpass Delta-Sigma modulator based on a time-interleaved SAR (Synthetic Aperture Radar) ADC (Analog-to-Digital Converter). The passive bandpass Delta-Sigma modulator comprises a two-path time-interleaved SAR ADC; the overall structure of the passive bandpass Delta-Sigma modulator is a two-channel modulator structure; each path of structure includes a pair of differential noise shaping modules; a DAC (Digital-to-Analog Converter) array in each path of SAR ADC is an MOM capacitor which consists of 511 unit capacitors with 9-bit output accuracy; and the SAR ADC in each path of channel also includes a four-input comparator and a successive approximation logic circuit. Through adoption of the modulator disclosed by the invention, the passband is transferred from low frequency to quarter sampling frequency. In the analog-to-digital conversion of an application requiring a specific frequency band, the speed and power expenditure of a circuit are greatly reduced through adoption of the basic structure of SAR ADC and a passive filter structure.

Description

technical field [0001] The invention belongs to the technical field of integrated circuits, in particular to a passive band-pass Delta-Sigma modulator based on time-interleaved SAR ADC. Background technique [0002] High precision, low power consumption, high speed analog-to-digital converter (Analog-to-Digital Converter, ADC) plays an irreplaceable role in the application of a large number of electronic systems. In the field of ultrasound imaging where the effective number of digits is more than 12 and the center frequency is tens of megabits, noise shaping ADCs, such as Delta-Sigma ADCs, are often selected. In recent years, due to technological progress, the noise-shaping successive approximation analog-to-digital converter SAR ADC can also achieve a sampling rate of hundreds of megabytes, but its accuracy is affected by factors such as reference voltage jitter and comparator noise, and it is difficult to achieve 12-bit Therefore, the combination of SAR ADC and passive fi...

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Problems solved by technology

[0004] Take the more common bandpass modulator that shifts the passband from low frequency to around a quarter of the sampling rate as an example. Compared with the traditional low-pass structure, the passband will be located in a higher spectral region, which can be modified by modifying the sampling rate Within a certain range (the sampling rate is below the limit speed of the circuit), the passband of the modulator covers the required frequency range of the application, that is, as long as the sampling rate meets four times the center frequency point, the best modulation effect can be achieved, while For the low-pass structure, if it is required to achieve the same sampling rate and cover the frequency band required by the band-pass structure, its oversampling rate must be less than twice, and the modulation effect is obviously not ideal.

[0005] However, the current low-power bandpass modulator design is still lacking, because of the particularity of the form of the bandpass transfer function, the typical design uses an active delta-sigma modulator structure, such as V.Sarma, N.A.Jacob, "A 250-MHz pipelined ADC-based fS / 4noise-shaping bandpass ADC," proposed by B.D.Sahoo, V.Narayanaswamy and V.Choudhary, IEEE Transactions on Circuits and Systems I: Regular Papers, vol.PP, pp.1-10 ,2017, although it achieves a high-precision band-pass noise shaping effect, its high power consumption is difficult to adapt to the application of ultrasound imaging

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