A high-resolution burst-mode laser transmitter with fast and accurate level monitoring for 1.25 Gb/s upstream GPONs

An innovative burst-mode laser transmitter (BM-TX) is presented for gigabit-capable passive optical network (GPON) upstream transmission at 1.25 Gb/s. The laser bias and modulation current each can reach 80 mA with a resolution of 0.1 mA providing a total drive current up to 160 mA. Both currents are generated by 10-bit current steering digital-to-analog converters (DACs), the architecture of which is specially adapted to yield a monotonic current setting at settling times below 12.8 ns. Tests show that fast automatic power control (APC) can stabilize and track the launched optical power with a tolerance of less than 1 dB over a wide temperature range for outdoor operation. The APC only requires a straightforward calibration of the "0" and the "1" level at room temperature. Optical level monitoring on strings of four consecutive "0" bytes and two consecutive "1" bytes at 1.25 Gb/s is demonstrated. APC based on such short strings of data has not been shown before. The circuits have been designed in a 0.35 /spl mu/m SiGe BiCMOS process. Experimental results show that this dc-coupled BM-TX meets the specifications of the recently approved ITU-T Recommendation G.984.2 supporting an intelligent power leveling mechanism (PLM).     

High-speed active-input cascode current mirror

A high-speed active-input cascode current mirror is presented. The proposed configuration combines a high output impedance with the high-frequency performance of a source- or emitter-driven active-input topology. Simulation results in a 0.35 /spl mu/m SiGe BiCMOS are presented to demonstrate the validation of the proposed current mirror. A much higher (about 30 to 40 times) output impedance is achieved, with no degradation in the high-frequency behaviour compared to conventional emitter-driven active-input current mirrors, without increasing the power consumption. The proposed configuration can be applied to both bipolar and CMOS technology.     

2.5 V passive CMOS mixer with 20 dBm P1 dB compression

A passive CMOS downconversion mixer with LO buffer is presented in 0.25 μm SiGe BiCMOS using a 2.5 V supply. With a 60 MHz RF signal input, measurements show that the conversion loss is 2.9 dB, the input-referred 1 dB compression point is 20 dBm and the inputreferred noise is 2146.8 dBm/Hz. Compared to conventional NMOS mixers, the 1 dB compression point is improved by 9.7 dB. The tradeoffs and the design of the LO buffer, which has a strong impact on the intermodulation distortion, are also presented.     

Development of GPON upstream physical-media-dependent prototypes

This paper presents three new gigabit-capable passive optical network (GPON) physical-media-dependent (PMD) prototypes: a burst-mode optical transmitter, an avalanche photodiode/transimpedance amplifier (APD-TIA), and a burst-mode optical receiver. With these, point-to-multipoint (P2MP) upstream transmission can be realized in a high-performance GPON at 1.25 Gb/s. Performance measurements on the new burst-mode upstream PMD modules comply with GPON uplink simulations. The laser transmitter can quickly set and stabilize the launched optical power level over a wide temperature range with better than 1-dB accuracy. A burst-mode receiver sensitivity of -32.8 dBm (BER=10/sup -10/) is measured, combined with a dynamic range of 23 dB at a fixed APD avalanche gain of 6. Full compliance is achieved with the recently approved ITU-T Recommendation G.984.2 supporting an innovative overall power-leveling mechanism.     

OSNR Penalty Imposed by Linear In-Band Crosstalk Caused by Interburst Residual Power in Multipoint-To-Point Networks

We present an analysis of linear in-band crosstalk in high split long reach wavelength/time-division-multiplexing passive optical networks (WDM-TDM PONs). In this letter, a mathematical model is deducted for the first time to calculate optical signal-to-noise ratio penalties due to in-band crosstalk in multipoint-to-point networks. The network performance can be perturbed by in-band crosstalk caused by power leakages from burst-mode optical network units (ONUs) in off-state. Our study results show that the leaked powers in upstream ONU transmitters can have an impact on the achievable split factor of WDM-TDM PONs. Furthermore, the performance limitations caused by aggregated interburst residual power are discussed.     

A 1.25-gb/s burst-mode receiver for GPON applications

This paper presents a 1.25-Gb/s burst-mode receiver (BMRx) for upstream transmission over gigabit passive optical networks (G-PONs). The dc-coupled receiver uses a unique arrangement of three limiting amplifiers to convert the bursty input signal to a current mode logic output signal while rejecting the dc offset from a preceding transimpedance amplifier. Peak detectors extract a decision threshold from a sequence of 12 successive nonreturn-to-zero (NRZ) 1's and 12 successive NRZ 0's received at the beginning of each packet. Automatic compensation of the remaining offsets of the BMRx is performed digitally via digital-to-analog converters. The chip was designed in a 0.35-/spl mu/m SiGe BiCMOS process. The receiver contains an APD with a gain of 6 and a transimpedance amplifier and shows a sensitivity of -32.8 dBm and a dynamic range of 23.8 dB. A sensitivity penalty of 2.2 dB is incurred when a packet with average optical power of -9 dBm precedes the packet under consideration, the guard time between the packets being 25.6 ns. The BMRx includes activity detection circuitry, capable of quickly detecting average optical levels as low as -35.5 dBm. The performed measurements prove that the receiver meets the G-PON physical media dependent layer specification defined in ITU-T Recommendation G.984.2.     

Simulations and Experiments on the Effective Optical Gain of FEC in a GPON Uplink

This letter studies the effective optical gain of Reed-Solomon (RS) forward-error correction (FEC) in a burst-mode gigabit passive optical network (GPON) uplink. Numerical simulations are made of the performance of an RS (255, 239) FEC code. For the first time, FEC performance is measured in a 1.25-Gb/s burst-mode GPON uplink in the presence of mode partition noise (MPN). Measurements show that the effective optical gain of RS (255, 239) can be considerably higher than 2.7 dB when MPN dominates     

2.5 V 35 dBm IIP3 75 MHz sixth-order active RC filter

A differential sixth-order Butterworth Sallen-Key lowpass filter in 0.25 mum SiGe BiCMOS, using a 2.5 V supply, is presented. The filter has a 75 MHz cutoff frequency and an attenuation of more than 20 dB at a stopband frequency of 148 MHz. The third-order intercept point (IIP3) is 35 dBm, providing excellent linearity.     

A digitally controlled on-chip monotonic reference current generator with low LSB current for fast and accurate optical level monitoring

This paper describes a digitally controlled on-chip monotonic Reference Current Generator (RCG) with 8-bit resolution and a LSB (Least Significant Bit) current as low as 100 nA. It was designed as a building block of a generic DC-coupled Burst Mode Laser Diode Driver (BM-LDD) for GPON (Gigabit Passive Optical Network) applications and acts as an on-chip RCG with a settling time of 18 ns for fast and accurate optical level monitoring with guaranteed monotony. The proposed architecture of the on-chip RCG is based on an 8-bit segmented current-steering Digital-to-Analog Converter (IDAC) and a bandgap voltage reference. The (3 + 5) segmented architecture of the 8-bit IDAC is an optimum combination of a 3-bit MSBs (Most Significant Bits) unit-element sub-DAC and a 5-bit LSBs binary-weighted sub-DAC offering good DNL (Differential Nonlinearity) performance. The bandgap voltage reference deviates only 0.6% of the nominal value over temperature and power supply variations. A cascade current mirror with a super beta helper circuit is used to guarantee monotony and high accuracy. The linearity errors caused by systematic influences and random variations are reduced by the proposed 2-D double centroid symmetrical architecture. Experiments confirm a DNL of ±0.5 LSB for the proposed RCG. The tested performance of optical level monitoring and APC (Automatic Power Control) algorithm is compliant to ITU-T GPON standards. The design was realized in a 0.35 μm SiGe BiCMOS technology with 3.3 V power supply. The technology choice was made by heavy requirements of the innovative DC-coupled 1.25 Gbit/s BM-LDD chip. Although the proposed structure was designed as a building block for a BM-LDD chip, the design concept can be applied for developing other high linearity on-chip RCG for a wide junction temperature range (?40 to 110°C).     

BiCMOS variable gain transimpedance amplifier for automotive applications

A new BiCMOS variable gain transimpedance amplifier with a large area integrated photodiode for automotive applications is presented. Through careful control of the input pole position and the frequency response of the core amplifier, the bandwidth of the transimpedance amplifier varies from 112 to 300 MHz when its gain changes from 14.2 kOmega to 400 Omega. The proposed circuit configuration maintains a high voltage across a common anode photodiode, and its bandwidth in highest gain varies from 121 to 102 MHz over a temperature range of -40 to +140degC. Simulation results in a 0.6 mum Si BiCMOS technology are given. The amplifier consumes 16 mW from a 3.3 V supply.