Spurious-free Dynamic Range Improvement Research Articles

Calibration of gain and timing mismatch for TI-ADCs with signals in all Nyquist zones using adaptive noise canceller

This paper presents a novel all-digital background calibration technique for general Time-Interleaved Analog-to-Digital Converters (TIADCs). Calibration of gain and timing mismatch of TIADCs using the estimation technique is designed based on the principle of the Adaptive Noise Canceller (ANC). In this ANC, there are two stages in gain, timing mismatch estimation in which a cascade structure of the correction and estimation is proposed to guarantee that our calibration achieves high performance. Besides the first Nyquit zone, the input signal at different Nyquist zones is also experimented. It is shown through the result that our calibration performs excellently on all chosen Nyquist zones. It achieves the SNDR (Signal to Noise Ratio) and SFDR (Spurious Free Dynamic Range) improvement of 19dB and 49dB, respectively. Moreover, the synthesized design with hardware co-simulation carried on the Xilinx Kintex-7 field-programmable gate array (FPGA) platform consumes only 7.36 % of the hardware resources of the FPGA chip and reduces the mismatch tone level to -87 dB. In addition, our convergence speed of SNDR during calibration is approximately 1/3 others.

An improved Random Swapping Thermometer Coding (RSTC) Dynamic Element Matching (DEM) method

ABSTRACT An improved Random Swapping Thermometer Coding (RSTC) Dynamic Element Matching (DEM) method is presented for Nyquist-rate Digital to Analog converters (DACs). In contrast to the RSTC DEM method, the presented method prevents the Spurious-free dynamic range (SFDR) reduction in DACs in low signal frequencies. Also, while ”RSTC with the restricted jumping technique” method is unable to prevent the SFDR reduction in low frequencies for non-full-scale sinusoidal signals, this new method prevents the SFDR reduction in low frequencies for both full-scale and non-full-scale sinusoidal signals. The Fast fourier transform (FFT) analysis for a behavioural model of a 6-Bit thermometer coded DAC at ( is the signal frequency and is the sample rate) shows 2.1 dB SFDR improvement in comparison to ”RSTC with the restricted jumping technique” method. In addition, the presented method achieves a reasonable trade-off between SFDR and Switching activity in comparison to other DEM methods.

Microwave Photonic Link With Improved SFDR Using Two Parallel MZMs and a Polarization Beam Combiner

This article presents a linearized microwave photonic link by means of two parallel Mach-Zehnder modulators (MZMs) and a polarization beam combiner (PBC). The proposed link exhibits significant suppression in third-order nonlinearity, which results in fifth order limited performance. Experiments are conducted and measured results demonstrate 17-dB improvement in spurious-free dynamic range (SFDR), resulting in a fifth order limited SFDR of 124 dB/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4/5</sup> . An Erbium Doped Fiber Amplifier (EDFA) and a high-power Modified Uni-Traveling Carrier (MUTC) photodiode are used to realize a link gain of 6 dB at 60 mA photocurrent for operation at 1 GHz. LTE signals with various instantaneous bandwidths centered at 1 GHz are delivered by the linearized link where spectral regrowth is dramatically suppressed.

A fully CMOS RF down-converter with 81.88 dB SFDR for IEEE 802.15.4 based wireless systems

In this paper, the challenges of dense integration, low power, low-cost, low-noise and high spurious free dynamic range (SFDR) required by the RF front-end (RFE) circuits for low-rate wireless personal area networks are addressed. The proposed RF down-converter circuit utilizes a low-noise transconductance amplifier stage to improve the noise performance of the highly noisy switching stage of the down-converter. The nonlinearity of the low-noise stage is compensated by employing post-distortion based harmonic cancellation for dynamic range improvement of the RF front-end circuit. The proposed RFE is designed and realised in UMC 180 nm CMOS process technology. The post-layout characterization of the circuit shows an third-order intercept point with reference to the input (IIP3) of 11.83 dBm, double-sideband noise figure of 5.9 dB, conversion gain of 17.87 dB and offers a SFDR of 81.88 dB while consuming 5 mA current from 1.8 V. The proposed circuit consumes an area of 0.1 mm2. The proposed RF down-converter boasts a 17 dB improvement in SFDR over the recently proposed RFE in the literature. The proposed RFE is also correlated with the other existing state-of-art RFE circuits recorded in the literature for Zigbee applications.

Compensation of dispersion-induced power fading with adjustment-free operation

A scheme for compensation of dispersion-induced power fading is proposed and experimentally demonstrated. The system transmits two modulated laser lights via a wavelength division multiplexer and a wavelength division demultiplexer. By optimizing the power ratio and the phase difference between the two modulated signals, the dispersion-induced power fading can be adequately compensated. A key significance of our approach is that no adjustments are required when the input radio frequency signal scans over a broad bandwidth of 1 to 12 GHz. We successfully demonstrate the compensation of the power fading for both 20- and 30-km fiber links. An improvement of spurious-free dynamic range is also achieved.

High Dynamic Performance Current-Steering DAC Design With Nested-Segment Structure

Dynamic performance of the current-steering digital-to-analog converter (DAC) is mainly affected by the mismatch-induced nonlinearity. Dynamic-element-matching (DEM) method has been widely employed to effectively improve the amplitude and timing mismatches. However, the maximum performance improvement is constrained by the conventional separate-segment structure for the current source array. In this brief, a DEM DAC with nested-segment structure is proposed to improve the mismatch performance. Compared with the best spurious-free dynamic range (SFDR) values obtained by the conventional DEM DACs, Monte Carlo simulations demonstrate that the proposed DAC achieves higher performance improvement with the same MSB bit width. The largest improvement occurs at MSB bit width of 3 with the 6.95- and 4.68-dB gain over two conventional designs, respectively. In terms of the digital complexity, the proposed architecture employs at least $2.7\times$ fewer multiplexers compared with the reported DEM DACs, while achieving comparable dynamic performance. Fabricated in 130-nm CMOS process, the proposed 12-bit 100-MS/s DAC occupies 0.21 mm2. Measurement results show that $1.9\times$ integral nonlinearity reduction ratio and 15.5-dB SFDR improvement from 46.6 to 62.1 dB at near Nyquist frequency are achieved.

Dual-wavelength linearization of analog photonic link based on PM–IM conversion

A novel method for linearization of phase-modulated analog photonic link is proposed in this paper. Heterodyne carrier source (HCS) is obtained by polarization multiplexing of two different-wavelength optical carriers. A Z-cut phase modulator (PM) which exhibits different electro-optic modulation indexes in orthogonal polarization states is used to modulate radio frequency signal onto the heterodyne optical carriers. Two channels of a WDM are used to filter out the positive or negative optical sidebands respectively and thus implement PM–IM conversion. The third-order intermodulation distortions (IMD3s) of the two different WDM channels are opposite in phase. IMD3 can be suppressed by combining signals from the two different WDM channels and adjusting the power ratio of the two optical carriers. Apart from the obvious improvement of SFDR, no need for bias control and easy adjusting of the power ratio make the method easy to implement. Experimental results show that the spurious free dynamic range (SFDR) of the system is improved by 14.54 dB.

A 14-bit 500-MS/s DAC with 211-MHz 70 dB SFDR bandwidth using TRI-DEMRZ

Time-relaxed interleaving dynamic element matching return-to-zero (TRI-DEMRZ) is proposed and verified in this paper to improve the spurious-free dynamic range (SFDR) of current-steering digital-to-analog converters (DACs). It incorporates time-relaxed interleaving (TRI), return-to-zero, and the dynamic-element-matching techniques, in a way that fosters the strength of each technique. As analyzed in this paper, merits beyond the combination of these techniques could be achieved. Firstly, TRI-DEMRZ provides a new dimension in the space domain, rather than the time domain, to explore the methods of mitigating nonlinear switching distortions. Secondly, this paper proves that, the image tone caused by typical channel mismatches between interleaved sub-DACs can be randomized into noise with TRI-DEMRZ. Circuit simulations and analysis are provided. An experimental 14-bit 500-MS/s current-steering DAC in 65 nm CMOS has been fabricated and measured, showing 81 dB SFDR at 5.5 MHz and more than 70 dB SFDR up to 211 MHz bandwidth. The SFDR improvement achieved by TRI-DEMRZ is more than 10 dB, which further verifies the effectiveness of TRI-DEMRZ.

Microwave Photonic Frequency Up-Convertor With Frequency Doubling and Compensation of Chromatic-Dispersion-Induced Power Fading

A novel photonic frequency-doubling up-convertor with compensation of chromatic-dispersion-induced power fading is proposed and experimentally demonstrated based on the cascaded structure of a Mach–Zehnder modulator (MZM) and a dual-parallel Mach–Zehnder modulator (DPMZM). The MZM is driven by a local oscillator signal biased at the null point for carrier-suppressed double-sideband modulation. The DPMZM is single-port driven by the intermediate-frequency signal and the other port is matched with a 50-Ω resistance. By adjusting the dc biases of the DPMZM, the power fading induced by chromatic dispersion can be compensated at any frequency. Experimentally, comparing with the conventional up-conversion radio-over-fiber link with cascaded MZMs, the power fading in 60 and 80 km fiber links can be successfully compensated and a 26.7 dB improvement in spurious-free dynamic range at 21.7 GHz for a link of 60 km can be achieved by using the proposed scheme.

A Single Channel Split ADC Structure for Digital Background Calibration in Pipelined ADCs

A digital background calibration technique based on the concept of split analog-to-digital converter (ADC) structure is proposed for pipelined ADCs to correct the gain error induced by the capacitors mismatch and finite dc gain of the residue amplifiers and nonlinearity of the residue amplifiers. In the proposed technique, one of the channels in split ADC structure is virtually implemented by using two extra comparators in each ADC’s stage and an interpolation filter to eliminate the mismatch between channels. Several circuit-level simulation results in the context of a 12-bit 100-MS/s pipelined ADC are provided to verify the usefulness of the proposed calibration technique. The simulation results show 51-dB signal-to-noise and distortion ratio and 65-dB spurious free dynamic range improvement, respectively, in comparison with the noncalibrated ADC.

A Linearized Tunable Single Bandpass Microwave Photonic Filter

In this letter, a tunable single bandpass microwave photonic filter (MPF) with an improved spurious free dynamic range (SFDR) based on a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. A phase-modulated double-sideband (DSB) signal is sent to a PS-FBG; when one of the sidebands falls in the notch of the reflection band of the PS-FBG, the reflected signal is converted to an intensity-modulated single-sideband (SSB) signal which leads to a single passband of the MPF. By tuning the wavelength of the optical carrier, the center frequency of the passband can be tuned correspondingly. The SFDR is improved by employing polarization mixing technique in a LiNbO3 phase modulator and a polarization diversity receiver. Experimental results show that the passband width and the frequency-tunable range of the single bandpass MPF are 80 MHz and 5.5 GHz, respectively. An SFDR improvement of 13.1 dB is successfully achieved.

A Novel High-Linearity Microwave Photonic Link Based on the Strategy of Adding a Compensation Path Using a Bidirectional Phase Modulator

A novel phase-modulation direct-demodulation microwave photonic link for improving the spurious-free dynamic range (SFDR) is proposed and experimentally demonstrated. In the proposed system, two different C-band optical wavelengths are modulated by a phase modulator in opposite directions. After combining the wavelengths, a fiber Bragg grating (FBG) is used to remove the optical spectrum between the two wavelengths. Because of the natural and wideband $\pi$ phase difference between the up and low optical sidebands after the phase modulation, third-order intermodulation distortion (IMD3) can be counteracted by subtly designing the optical power and modulation depth relationships between the two wavelengths. The experimental results show that IMD3 is reduced by 28.6 dB, achieving an SFDR improvement of 20 dB compared to a traditional single sideband phase-modulation microwave photonic link.

Dynamic Range Improvement for an Analog Photonic Link Using an Integrated Electro-Optic Dual-Polarization Modulator

A novel analog photonic link with enhanced spurious-free dynamic range (SFDR) based on an integrated electro-optic dual-polarization modulator is presented and demonstrated. The dual-polarization modulator, which consists of a polarization beam splitter, a polarization beam combiner, and two z-cut LiNbO 3 MZMs, can achieve complementary intensity modulation along the orthogonal polarization directions with different modulation indexes. By properly adjusting the power relationship of the orthogonal polarization directions, two third-order intermodulation distortions (IMD3) have equal intensity and opposite phase and cancel each other out. Combined with a low-biasing technique to reduce the noise power, the SFDR of the link can be further improved. A theoretical analysis is presented and validated by a simulation. The IMD3 can be suppressed by 30.6 dB, giving an improvement in SFDR of about 22 dB compared with a conventional optical double-sideband modulation link.

Power photodiodes for high dynamic range photonic links

High-power photodiode applications for multioctave high dynamic range links are presented. A review of modulator and photodiode distortion analysis is given as well as an introduction to polarization-dependent loss distortion as it pertains to such systems. A new analysis of the photodiode distortion contributed degradation of spurious free dynamic range (SFDR) is developed. Experimental data covers high-power photodiodes for zero-bias high dynamic range links, showing significant improvement in SFDR. A link is presented showing the degradation of link performance when polarization-dependent loss is added into the system. A summary of state-of-the-art device performance is covered as well as the outlook on future applications for power photodiodes in analog photonic links requiring high SFDR.

Dynamic Range Improvement of IM-DD Optical Link using Dual-Wavelength Dual-Parallel Modulation

In this paper, we present an incoherent dual-parallel modulation linearized optical link employing two different optical wavelengths. Comparing with previous dual-parallel modulation, this linearization method prevents the recreation of distortion products and can be readily implemented. Furthermore, a dual-wavelength dual-parallel modulation linearized optical link constructed with the commercially available devices is experimentally demonstrated with a spurious-free dynamic range of <TEX>$122.5dB.Hz^{4/5}$</TEX>. More than 25 dB suppression of the intermodulation distortion, 15.6 dB improvement of spurious-free dynamic range and 1.5 dB improvement of compression dynamic range are achieved after linearization.

Spurious-free dynamic range improvement in a photonic time-stretched analog-to-digital converter based on third-order predistortion

Spurious-free dynamic range (SFDR) limited by intermodulation distortions is a usually accepted measure for dynamic performance of a photonic time-stretched analog-to-digital converter (ADC). In this paper, SFDR improvement in a photonic time-stretched ADC based on third-order predistortion is proposed. The third-order predistortion is achieved optically within an integrated dual-parallel Mach–Zehnder modulator (DPMZM). The mechanism of SFDR improvement with third-order predistortion in the DPMZM is theoretically analyzed. Compared with a conventional scheme without predistortion, the experimental results show that the SFDR improvement of ∼26 dB in the proposed scheme is proved. [Publisher's Note: This paper is part of the Microwave Photonics special issue published in Photonics Research, Vol. 2, No. 4. It was mistakenly published in Issue No. 5.]

Improved linearity in down-converted analog photonic link by polarization manipulation

A method to improve the linearity of the down-converted analog photonic link is proposed and experimentally demonstrated, consisting of two phase modulators, a polarizer, and an optical filter. Down-conversion of a 10-GHz microwave signal to 100-MHz intermediate frequency is successfully achieved. By carefully optimizing the angles between the transverse-electric and transverse-magnetic modes, the third-order inter-modulation distortion (IMD3) is suppressed. The linearization method leads to a suppression of the IMD3 by more than 14 and 13 dB improvement of spurious-free dynamic range.

A high-speed offset cancelling distributed sample-and-hold architecture for flash A/D converters

A 6-bit high-speed analog-to-digital converter was implemented utilizing a novel distributed sample-and-hold architecture capable of sampling and subtracting the input preamplifier's offset. This architecture offers substantial improvement in the high-speed operation of the converter. Compared to the prior-art, the effective number of bits improves 0.8bit. The spurious free dynamic range improvement is over 12dB. In addition the implemented technique uses half the number of capacitors compared to similar designs. The converter achieves over 5.2bit resolution up to the Nyquist input signal frequency. A simple but effective design methodology is also presented.

Dynamic range improvement of a microwave photonic link based on bi-directional use of a polarization modulator in a Sagnac loop

A novel microwave photonic link (MPL) with an improved spurious-free dynamic range (SFDR) based on a bidirectional use of a polarization modulator (PolM) in a Sagnac loop is proposed and demonstrated. The PolM in the loop functions, in conjunction with a polarization controller and a polarization beam combiner, as a Mach Zehnder modulator (MZM), which only modulates the incident light wave along the clockwise direction, leaving the counter-clockwise light wave unmodulated due to the velocity mismatch. Two clockwise intensity-modulated signals along two paths (Path 1 and Path 2) are generated, with one (Path 2) combined with the non-modulated light wave from the counter-clockwise direction to suppress part of the optical carrier. By controlling the power relationship between the two paths, the third-order intermodulation distortion (IMD3) can be fully suppressed, and thus an MPL with improved dynamic range is achieved. A theoretical analysis is presented, which is validated by an experiment. The IMD3 can be suppressed by 50 dB, giving an improvement in SFDR of 16 dB.

RF up/down-conversion based on optically injection-locked VCSEL

All-optical radio frequency conversion is proposed by directly modulated optically injection-locked vertical-cavity surface-emitting lasers. The enhancement effect of second order products of RF signals by OIL technique is analyzed based on reflection-mode OIL model. Simulation results show that high injection ratio and large wavelength detuning of OIL condition lead to a high RF conversion gain. Compared with free running condition, more than 20 dB RF conversion gain enhancement is achieved in the simulation. The experimental results of the RF conversion gain improvement (+ 18 dB) by OIL show excellent agreement with our simulation results. The spurious free dynamic range improvement (+ 15 dB) of conversion signals by OIL is also experimentally demonstrated.