Fig. 1.
Receiver architecture for multi-mode multi-band standard.
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Chenluan Wang, Shengxi Diao, Fujiang Lin. A low-power time-domain VCO-based ADC in 65 nm CMOS[J]. Journal of Semiconductors, 2014, 35(10): 105009. doi: 10.1088/1674-4926/35/10/105009
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C L Wang, S X Diao, F J Lin. A low-power time-domain VCO-based ADC in 65 nm CMOS[J]. J. Semicond., 2014, 35(10): 105009. doi: 10.1088/1674-4926/35/10/105009.
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A low-power time-domain VCO-based ADC in 65 nm CMOS
DOI: 10.1088/1674-4926/35/10/105009
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Abstract
A low-power, high-FoM (figure of merit), time-domain VCO (voltage controlled oscillator)-based ADC (analog-to-digital converter) in 65 nm CMOS technology is proposed. An asynchronous sigma-delta modulator (ASDM) is used to convert the voltage input signal to a square wave time signal, where the information is contained in its pulse-width. A time-domain quantizer, which uses VCO to convert voltage to frequency, is adopted, while the XOR (exclusive-OR) gate circuits convert the frequency information to digital representatives. The ASDM does not need an external clock, so there is no quantization noise. At the same time, the ASDM applies a harmonic-distortion-cancellation technique to its transconductance stage, which increases the SNDR (signal to noise and distortion ratio) performance of the ASDM. Since the output of the ASDM is a two-level voltage signal, the VCO's V-F(voltage to frequency) conversion curve is always linear. The XOR phase quantizer has an inherent feature of first-order noise-shaping. It puts the ADC's low-frequency output noise to high-frequency which is further filtered out by a low-pass filter. The proposed ADC achieves an SNR/SNDR of 54. dB/54.3 dB in the 8 MHz bandwidth, while consuming 2.8 mW. The FoM of the proposed ADC is a 334 fJ/conv-step.-
Keywords:
- VCO,
- ADC,
- ASDM,
- PWM (pulse width modulation),
- nonlinearity,
- low-power
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References
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