Ehsan Zia, Ebrahim Farshidi and Abdolnabi Kosarian
Pipelined analog-to-digital converters (ADCs) are widely used in electronic circuits. The purpose of this paper is to propose a new digital background calibration method to…
Abstract
Purpose
Pipelined analog-to-digital converters (ADCs) are widely used in electronic circuits. The purpose of this paper is to propose a new digital background calibration method to correct the capacitor mismatch, finite direct current (DC) gain and nonlinearity of residue amplifiers in pipelined ADCs.
Design/methodology/approach
The errors are corrected by defining new functions based on generalized Newton–Raphson algorithm. Although the functions have analytical solutions, an iterative procedure is used for calibration. To accelerate the calibration process, proper initialization for the errors is identified by using evaluation estimation block and solving inverse matrix.
Findings
Several behavioral simulations of a 12-bit 100MS/s pipelined ADC in MATLAB indicate that signal-to-(noise + distortion) ratio (SNDR) and spurious free dynamic range (SFDR) are improved from 30dB/33dB to 70dB/79dB after calibration. Calibration is achieved in approximately 2,000 clock cycles.
Practical implications
The digital part of the proposed method is implemented on field-programmable gate array to validate the performance of the pipelined ADC. The experimental result shows that the degradation of SNDR, SFDR, integral nonlinearity, differential nonlinearity and effective number of bits is negligible according to fixed-point operation vs floating-point in simulation results.
Originality/value
The novelty of this study is to use Newton–Raphson algorithm combined with appropriate initialization to reduce the number of divisions as well as calibration time, which is suitable in the recent nano-meter complementary metal oxide semiconductor technologies.
Details
Keywords
Seyed Ali Sadat Noori, Ebrahim Farshidi and Sirus Sadoughi
Digital Delta Sigma Modulator (DDSM) is used widely in electronic circuits including Radars, class-D power amplifiers and fractional frequency synthesizers. The purpose of this…
Abstract
Purpose
Digital Delta Sigma Modulator (DDSM) is used widely in electronic circuits including Radars, class-D power amplifiers and fractional frequency synthesizers. The purpose of this paper is to propose an implementation for MASH DDSMs named as Multi Modulus Reduced Complexity (MMRC) architecture.
Design/methodology/approach
This architecture will use a very simple pseudorandom Linear Feedback Shift Register (LFSR) dither signal with period N_d to randomize the digital MMRC modulator used for fractional frequency synthesizers. Using error masking methodology, the MMRC modulator can decrease the hardware consumption and increase accuracy of the fractional frequency synthesizer. Rules for selecting the appropriate word lengths of the constituent MMRC modulator are derived.
Findings
This paper contains three modulators. The first stage modulator is a variable modulus First Order Error Feedback Modulator and has a programmable modulus M1 that is not a power of two. The second and third stage modulators are the first order pseudorandom LFSR dithered MASH 1-1 and modified MASH 1-1-1, which have conventional modulo M2, M3, respectively. With optimum selection modulus M1, the new structure can synthesize the desired frequency exactly. Simulation results confirm the theoretical predictions. Also the results of circuit implementation proposed method reports 13 per cent reduction in hardware.
Originality/value
This paper for the first time proposes a nested sigma delta modulator with a pseudorandom shaped dither signal which reduced hardware complexity and increased the period of output signal. This modulator is exploited in the fractional frequency synthesizer to the output frequency can be set more accurately.