Analysis of noise immunity at common circuits of the front end parts of high-speed transceivers S.V. Kondratenko NRNU MEPhI ICPPA-2016,

The proposed system of parameters of drivers noise immunity Comparing of different drivers types at noise immunity The simulation results of test examples Conclusions Plan ICPPA-2016,

Investigated objects Alternative names of analog (A) blocks of the transceivers:... interface (or front end) parts... peripheral parts... i/o buffers. Next, use the term “analog”. The focus is on the analog parts of the transmitters (drivers) due to large pulse current in their output stages, and increased sensitivity to the parasitic inductance in the common circuits (power and ground circuits). 3 ICPPA-2016,

The problem of noise immunity in the drivers VML driver The stylized eye diagrams for DTX = TXP-TXN output considering the influence of noises at common circuits Opened keys are connected to the outputs of noisy power and ground buses, leading to a collapse of the eye. Internal noises U n.int are correlated with the transmitted signal unlike interference received from the digital part of the transmitter U n.ext. The blur of eye diagrams increases due to the influence of parasitic RLC elements of package pins and parasitic capacitors C P on the outputs. Through current i THR is grounded in different ways on HF, in general, the noises on common circuits are not in phase and are not suppressed completely in the load. ICPPA-2016,

The proposed system of noise immunity parameters of the drivers Input nodes Output nodes Z 11 - K 13 K 14 K 1,3-4 Input impedance neglecting influence TC for a single signal TC for a differ. signal 2 - Z 22 K 23 K 24 K 2,3-4 neglecting influence input impedance TC for a single signal TC for a differ. signal TC –transfer coefficient Standard for OpAmp parameter PSRR (Power Supply Rejection Ratio) is analogous to the K 1,3-4 coefficient, but in general the proposed system of parameters describes the noise immunity of drivers for different values of parasitic elements more fully and accurately. You can directly compare the parameters Z ii, K ij for different drivers to assess their general noise immunity at common circuits. Model parameters are calculated and analyzed in the frequency domain (ac), which simplifies findings and speeds up calculations. ICPPA-2016,

Compared types of drivers Principle of operation: switching to the load reference... currentvoltage Conditions of the equivalence: general identical dimensions of the transistors at outputs (for LVDS-driver - after scaling) the same load resistance R L = 100 ohms the same own output impedance of 100 ohms... and private (for numerical simulation) 0.18 micron CMOS technology target 800 mV swing of differential output signal (for drivers operating in voltage mode sweep vdd/2) the same parasitic elements (C P = 5 pF, L = nH at common circuits). VMLnVML Pseudo-LVDS (simplified) CML ICPPA-2016,

Calculated values of the parameters of noise immunity for compared drivers Input nodes Output nodes Ohm-0,490,300, Ohm0,700,510,21 Pseudo-LVDS at vin={1,0}, changes at vin={0,1} Input nodes Output nodes ,2 kOhm-0,010,030, Ohm0,340,810,47 nVML Input nodes Output nodes Ohm-0,790,450, Ohm0,190,540,35 CML Input nodes Output nodes Ohm-0,700,230, Ohm0,280,780,50 VML 7 ICPPA-2016,

Findings of the analysis and calculations of the drivers  According circuitry - only LVDS-driver output signal levels are not adhered to one or both of the common buses, which increases noise immunity.  According output impedance - CML-driver has the lowest impedance (43 ohms in this case), which should increase the impact of noise on general circuits due to the prevailing inductive reaction of the impedance of power and ground pins.  According transfer coefficients - the smallest differential noise transfer coefficient has LVDS-driver, the greatest - VML-driver.  The tabulated values of the asymptotic impedances and transfer coefficients in fact depends on the frequency (decrease on HF), which may change the comparison results. ICPPA-2016,

Simulated circuit of the TX-RX path and conditions of the simulation Conditions of the simulation: - at the input - a random 8b10b encoded signal at a rate of 1.25 Gbps (1X) - normal conditions PVT - for the CML, VML and nVML drivers the same type of receivers are used, for the pseudo-LVDS driver - differed receiver with the power supply 2.5 V for input stage. 9 ICPPA-2016,

Eye diagrams: 1,25 Gbps, TQFP-208 package RX inputs RX outputs All TX-RX pairs are successfully working, but pseudo-LVDS driver is better ICPPA-2016,

Eye diagrams: 2,5 Gbps, TQFP-208 package Drivers sequence in order of preference: VML (worst) nVML CML Pseudo-LVDS (best) This is consistent with previous findings on the basis of parameters of noise immunity. 11 ICPPA-2016,

CONCLUSION 1.In the early stages of designing high-speed transceiver in serial channels it is advisable to take into account the effect of parasitic constructive elements in order to choose among alternative realizations of analog parts of the transmitter and receiver. 2.To evaluate the noise immunity of the analog parts on common circuits (power and ground) the system of parameters proposed including impedances of interested nodes and transmission coefficients on their driver outputs. This system includes a standard parameter PSRR, but in general it describes the noise immunity of drivers for different values ​​ of parasitic elements more fully and accurately. 3.Comparison of parameters of noise immunity for the four types of drivers showed the advantage of pseudo-LVDS drivers. This was confirmed in the simulation transmitter-receiver path, designed in 0.18 micron CMOS technology with regard parasitic package parameters such as TQFP-208 and running at speeds up to 2,5 Gbps. 4.Used system of noise immunity parameters forms a specialized macro model of the drivers to analyze their noise immunity on common circuits. In contrast to the IBIS-model parameters proposed linearized macro models are determined by calculation or analysis in the frequency domain, less labor-intensive than calculations or analysis in the time domain. ICPPA-2016,

Thank you for attention! ICPPA-2016,