A 28.4–30.5‐Gb/s Reference‐Less Full‐Rate Clock and Data Recovery With Current Mismatch Elimination in 28‐nm CMOS

A clock and data recovery (CDR) circuit for 10 Gb/s broadband communication using a CMOS process is presented. The circuit makes use of a novel adjustable K/sub pd/ phase detector. The phase detector can provide a binary characteristic or a linear characteristic under different control voltages. The CDR core circuit consists of a phase frequency detector, an integrator, a LC VCO and a low pass filter provided off-chip. Two more phase detectors, a bang-bang phase detector and a Hogge phase detector, are also built in the circuit for performance comparison.

In this brief, a half-rate (HR) bang-bang (BB) phase detector (PD) with multiple decision levels is proposed for clock and data recovery (CDR) circuits. The combination allows the oscillator to run at half the input data rate while providing information about the sign and magnitude of the phase shift between the PD inputs. This allows a finer control of the frequency of the oscillator in the phase-locked loop (PLL) of the CDR circuit, which results in up to 30% less output clock jitter than with a conventional two-levels HR BB PD. Thanks to this, the bit error rate can be decreased by up to $5\times $ in a 5-Gb/s CDR circuit. The proposed topology was implemented in a 28-nm FDSOI CMOS technology providing average power consumption below $76~\mu \text{W}$ with a supply voltage of 1 V. Although multilevel (ML) BB PDs have already been proposed in some PLL-based CDR with very interesting results, a specific design of the PD has to be implemented for an HR system. This brief provides the first ML-HR-BBPD.

Bang-bang clock and data recovery (BBCDR) circuits are severely nonlinear systems as a result of the binary phase detector's nonlinear behavior. The characteristic of the bang-bang phase detectors follows ideally the sign function, but in practice, it exhibits a finite slope across a narrow range of the input phase difference. In this brief, by considering an approximated practical model for the phase detector, the nonlinear differential equation of the system is obtained which shows that the BBCDR is a nonlinear system with memory and VOLTERRA series expansion is useful for such systems. As a result, the jitter generation of voltage-controlled-oscillator phase noise in BBCDR is specified. Behavioral simulation is used to validate the analytical results. The results show a good agreement between analytical equations and simulation results.

This paper provides an in-depth analysis of the third-order bang-bang clock and data recovery (BBCDR) circuit, which accurately predicts its operating characteristics, namely, the jitter transfer function (JTF), the jitter tolerance (JTOL), and the jitter generation (JGEN). By formulating the time-domain waveforms, we introduce a characterizing method and also derive the closed-form equations and their simplified versions under specific conditions, which are related with the second-order loop filter (LF). Our framework is consistent with the conclusions of the prior works. Also, we discuss through the time-domain behavior, the sinking area of the JTOL and other specific phenomenon appearing in the third-order BBCDR loop. We verify all above prediction by system-level simulations with the MATLAB/simulink model.

A clock and data recovery (CDR) circuit is one of the crucial blocks in high-speed serial link communication systems. The data received in these systems are asynchronous and noisy, requiring that a clock be extracted to allow synchronous operations. Furthermore, the data must be retimed so that the jitter accumulated during transmission is removed. This paper presents a novel architecture of CDR, which is very tolerant to long sequences of serial ones or zeros and also robust to occasional long absence of transitions. The design is based on the fact that a basic clock recovery having a clock recovery circuit (CRC) and a data decision circuit separately would generate a high jitter clock when the received non-return-to-zero (NRZ) data with long sequences of ones or zeros. To eliminate this drawback, the proposed architecture incorporates a data circuit decision circuit within the phase-locked loop (PLL) CRC. Other than this, a new phase detector (PD) is also proposed, which was easy to accomplish and robust at high speed. This PD is functional with a random input and automatically turns to disable during both the locked state and long absence of transitions. The voltage-controlled oscillator (VCO) is also designed delicately to suppress the jitter. Due to the high stability, the jitter is highly reduced when the loop is locked. The simulation results of such CDR working at 1.25Gb/s particularly for 1000BASE-X Gigabit Ethernet by using TSMC 0.25μm technology are presented to prove the feasibility of this architecture. One more CDR based on edge detection architecture is also built in the circuit for performance comparisons.

This article reports a single-loop full-rate bang-bang clock and data recovery (BBCDR) circuit supporting a four-level pulse amplitude modulation (PAM-4) pattern. We eliminate both the reference and the separate frequency detector (FD) by deliberately adding two fixed strobe points in the bang-bang phase detector (BBPD) curve via a clock-selection scheme. As such, we can achieve a wide frequency-capture range in a single-sided FD polarity. The BBPD also incorporates a hybrid control circuit to automate the frequency acquisition over a wide frequency range. Prototyped in a 28-nm CMOS, the proposed BBCDR occupies a tiny area of 0.0285 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and exhibits a 23-to-29-Gb/s capture range. The acquisition speed [8.2 Gb/s/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> ] and energy efficiency (0.68 pJ/bit) compare favorably with the state of the art.

This paper presents a technique to extend the frequency acquisition range for bang-bang phase-detector-based clock and data recovery (CDR) circuits without an additional frequency acquisition loop or lock detection circuit. The per-manent modulation of the offset current in the CDR's integral branch enhances the acquisition range by nearly 4 times, covering the entire tuning range of the voltage controlled oscillator. The increase in power dissipation and the chip area are negligible. This technique was implemented and measured in a 28 Gbps NRZ bang-bang CDR chip to confirm the working principle. In addition to the increased acquisition range, the CDR also surpasses jitter related specifications from the OIF CEI-28G-VSR standard.

This paper reports a reference-less single-loop bang-bang clock and data recovery (BBCDR) circuit featuring fast and robust frequency acquisition without identifying the frequency error polarity. The key idea is a deliberately-current-mismatch charge-pump pair, which avoids the need of a complex high-speed data path or clock path during frequency acquisition. Prototyped in 28nm CMOS, our BBCDR covers a 47.6-to-58.8Gb/s PAM-4 input automatically. The achieved energy efficiency (≤0.25pJ/bit) and acquisition speed <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$[9.8(\text{Gb}/\mathrm{s})/\mu\mathrm{s}]$</tex> compare favorably with the prior art. Keywords—CMOS, reference less, single loop, half-rate, bang-bang clock and data recovery (BBCDR), frequency detector (FD), charge pump (CP), 4-level pulse amplitude modulation (PAM-4), zero (ZNC), positive (PNC), and negative (NNC) net current.

Purpose – Bang-bang clock and data recovery (BBCDR) circuits are hard nonlinear systems due to the nonlinearity introduced by the binary phase detector (BPD). The specification of the CDR frequency response is determined by jitter tolerance and jitter transfer. In this paper, jitter transfer and jitter tolerance of the BBCDR are characterized. The paper aims to discuss these issues. Design/methodology/approach – The presented method is general enough to be used for designing the BBCDR loop parameters to meet SONET jitter transfer requirements (loop bandwidth and jitter peaking). Findings – In this paper, jitter transfer and jitter tolerance of the BBCDR are characterized by formulating the time domain waveforms. As a result, a new equation is presented to obtain angular frequency. Also, the jitter tolerance is expressed in closed form as a function of loop parameters. The validity of the resulted equations is verified through HSPICE simulations using TSMC 0.18-μm CMOS process. Simulation results show that good conformance between analytical equations and simulation results. Originality/value – The proposed approach offers two advantages compared to conventional designing methods. First, this approach does not consider any value restriction to the capacitor. Second, a new condition has been presented to guarantee that the value of jitter peaking is approximately zero. The presented method is general enough to be used for designing the BBCDR.

In dual-loops clock and data recovery (CDR) circuit design, lock detector is crucial in controlling the switching within CDR loop. The setting of the frequency accuracy of lock detector is a tough task as large ppm will leads to a longer lock time for phase tracking loop and small ppm will leads to more switching time between the loops. A novel lock detector with hysteresis property is proposed in this paper. It provides two different ppms in both different conditions; a smaller ppm for in-lock condition and a larger ppm for out-of-lock condition. This paper also provides a detailed analysis of the proposed lock detector at different conditions. The proposed lock detector is simulated in 0.18-um technology and it consumes 1.1-mW at a 1.8V supply voltage.

We present a 40-Gbit/s-class clock and data recovery (CDR) circuit with a new lock detector. The lock detector operates robustly with a linear-type phase detector. The CDR IC was fabricated using InP/InGaAs HBTs. Error-free operation and wide eye opening were confirmed for 40, 43, and 45-Gbit/s PRBS with a length of 2/sup 31/-1. By attaching a frequency search and phase control (FSPC) circuit to the chip, the CDR circuit pulls in throughout a 39-45 Gbit/s range. The fabricated IC dissipates 1.89 W at a supply voltage of -4.5V.

This paper reports a reference-less frequency-detector-less single-loop bang-bang clock and data recovery (BBCDR) circuit featuring wide frequency acquisition. We use a current-starved ring oscillator controlled by a 5-bit resistive digital-to-analog converter to maintain quarter-rate operation, supporting a capture range of 110.4%. By the virtue of a deliberate-current-mismatch charge pump pair, we form the single-sided capture scheme in the frequency detection characteristic, eliminating the power-hungry circuits in the high-speed clock and data paths. Employing a hybrid control circuit, the proposed BBCDR automates frequency acquisition and phase tracking in the overall 32 bands. Prototyped in a 65-nm CMOS, the BBCDR covers a wide data rate from 10.8 to 37.4 Gb/s, achieving an acquisition speed of 4.63 (Gb/s)/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula> s and an energy efficiency of 1.3 pJ/bit.

Continuous-rate referenceless clock and data recovery (CDR) circuits are capable of operating over a wide range of data rates in multiple standards. To achieve wide-range operation without an external reference clock, several frequency detection techniques are presented [1]–[5]. However, most of the previous techniques require considerable hardware and power overhead to obtain information for frequency detection. It leads to a performance tradeoff between capture range, lock time, and power consumption. As well as the performance aspects, they rarely address significant concerns such as compatibility with the conventional CDR architecture, transition from phase locking to frequency locking, and harmonic locking. In this work, a referenceless CDR employing a stochastic phase-frequency detection technique is proposed. While the proposed CDR architecture is almost similar to the conventional bang-bang CDR, it achieves an unlimited frequency detection capability by adopting a machine learning (ML)-inspired design procedure. The design procedure finds optimal weights for both phase and frequency detection utilizing the same information as the bang-bang phase detector (BBPD). As a result, the proposed technique achieves low-power, wide-range operation with minimal hardware overhead while overcoming the conventional logical approaches. Moreover, a robust operation without the transition and harmonic locking issues is obtained.

We describe a 40-Gbit/s-class clock and data recovery (CDR) circuit with an extremely wide pull-in range. A Darlington-type voltage-controlled oscillator (VCO) is newly designed to cover the STM-256/OC-768 full-rate-clock frequencies with a wide frequency margin. We also describe a new lock detector using an exclusive-NOR gate. The CDR IC was fabricated using InP/InGaAs HBTs. Error-free operation and wide eye opening were confirmed for 40-, 43-, and 45-Gbit/s PRBS with a word length of 2/sup 31/ - 1. We attached a frequency search and phase control (FSPC) circuit to the chip as a new frequency acquisition aid, and this allows the CDR circuit to pull in throughout a 39-45-Gbit/s range. The peak-to-peak and rms jitter of the recovered clock were 3.6 and 0.48 ps, respectively.

The CDR (Clock and Data Recovery) using PLL with Bang-Bang PD (Phase Detector), CP (Charge Pump), and RC (Resistor and Capacitor) filter is widely used in Serdes circuits. This paper provides a detailed analysis to Bang-Bang CDR's dynamic behaviors and jitter tolerance. Then the slewing conditions, locking condition, and jitter tolerance curve, which are verified by a model implemented in Simulink, are proposed for choosing the filter parameters when designing the circuits.