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10GEPON Burst Receiver Ad-hoc

This ad-hoc aims to resolve issues such as TIA gain, guard time, and architectural preferences, emphasizing the importance of variable TIA gain for optimal performance in both 1G and 10G bursts. It delves into TIA parameters, noise considerations, and AGC loop timing, highlighting the impact on receiver sensitivity and noise levels. Discussions on AC vs. DC coupling, CID length, and AGC response dynamics further enhance understanding of optimizing 10GEPON burst receivers.

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10GEPON Burst Receiver Ad-hoc

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  1. 10GEPON Burst Receiver Ad-hoc

  2. Goals • The goals of this ad-hoc are to resolve the following issues: • TIA Gain • Is different gain for 1G and 10G required? • 10GEPON Burst Receiver architecture • AC Coupled? or DC Coupled? • Guard Time • Is different Guard Time between Bursts of different data rate required?

  3. Outline • Optical Receiver – Basic • TIA Parameters • LIA - AC vs. DC Coupled • Preamble Length

  4. Clock CDR LIA TIA Data Offset Compensation AGC V(t) t i(t) V(t) t t Optical Receiver Architecture

  5. 10GEPON TIA

  6. RFB -A Vout Iin CT TIA Parameters • The primary function of the TIA is to convert the small current, from the photodiode, into a voltage while adding as little noise as possible to the output signal APD TIA optimized for 10G Source 1: 1.25Gbps 8B10B Coding 1.25Gbps LIA Source 2: 10.3125Gbps 64B66B Coding 10.3125Gbps LIA ? • TIA is characterized by several parameters: • Transimpedance Gain • Input Referred Noise • Bandwidth • One of the main “problems” of the TIA is the trade-off between Gain, Noise and Bandwidth

  7. TIA – Bandwidth, Gain, and Noise • All 3 parameters of the TIA are function of the RFB • Bandwidth: The Transimpedance gain is equal to the RFB, while the Bandwidth is determined by the RC time constant. • Gain: Transimpedance gain of the TIA is the ratio of the output voltage to the input current. • Noise: Noise contribution of the TIA is characterized by the input referred noise current • The input referred noise current is related to the output noise voltage by the following equation:

  8. TIA Gain Burst Parameter - Different for 1G and 10G? • In order to optimize the performance of the TIA in both 1G and 10G we need to support Variable TIA Gain • Gain can be varied between 1G and 10G bursts by changing the feedback resistor • In order to analyze the impact on TIA performance in 1G, we need to calculate the SNR of the TIA

  9. TIA – Input Referred Noise • The ultimate limitation on the Optical Receiver sensitivity is the Noise • The noise includes the Photodiode’s Shot Noise and the noise added by the TIA • The major noise sources are the Feedback Resistor and Voltage Amplifier di²Rf Rf Rout di²AMP di²eq,in gm Cout Cin CDiode

  10. Preamble length – function of maximum CID (Consecutive Identical Digits) • The data signal has a sequence of consecutive high and low bits in the middle of the sequence • The DC level during the consecutive bits begins to droop • Long sequence of consecutive bits can significantly change the DC level of the data and the optimum threshold voltage • A poor low frequency cut-off vertically closes the eye diagram and can reduce the sensitivity of the system • In order to achieve a lower low frequency cut-off, we need to extend the number of preamble bits • For example, in GPON, the CID is 72 bits

  11. TIA – AGC Loop Timing Peak Detector output Noise • TIA AGC initialization time parameter needs to be much longer than the CID bit time • During “0” CID, the AGC loop should remain constant and not “running” to infinite gain • In between Bursts, the AGC needs long preamble, greater than AGC_τto enable AGC to “learn” new peak value idiode TIA_Gain Amplified Noise TIA_Output

  12. TIA – AGC Response Delay V 1.2 1.0 0.8 0.6 0.4 0.2 0 t -120 -80 -40 0 40 80 120 τagc • Practical AGC has delayed response to signal-level change

  13. 10GEPON LIA

  14. The Problem – AC or DC Coupled APD TIA optimized for 10G Source 1: 1.25Gbps 8B10B Coding 1.25Gbps LIA Source 2: 10.3125Gbps 64B66B Coding 10.3125Gbps LIA ? ?

  15. 10G LIA – AC Coupled • 10G LIA is simulated by the following Transfer Function • The lower cut-off pole (f1) determine the CID length, while the higher cut-off pole (f2) determine the Bandwidth • For the lower frequency, 3MHz was simulated • For the higher frequency, 7GHz was simulated • In order to maintains minimum DC droop from the baseline, we need at least factor 4 over the τ 3dB 3MHz 7GHz

  16. 10G LIA – DC Coupled • In DC-coupled the RC (τ) is determined by internal capacitors • One capacitor for “fast” acquisition during preamble - and the second for CID support • During reception of the preamble, the threshold acquisition done by the “high” frequency cut-off pole, then switching to the “low” frequency cut-off pole to support CID

  17. Transfer Function 3dB A: forward gain. K: feedback gain. WL: lowpass pole frequency (in feedback loop). WH: highpass pole frequency (in forward path). f1 = 3MHz f2 = 80MHz • f1 and f2 determine how much DC droop we are allowed from the baseline • During preamble we use f1_high then after “short” time we switch to f1_low to support CID

  18. An example: CID = 64 X = 0.1 (10%) N = -4 * 64 = 2430bits ln(1 - 0.1) Preamble Length - A Formula • Assuming that 4 time constants is needed Where: = Number of CID = Required Preamble length [bits] = Deviation of baseline permitted during CID Just to the LIA For 5% droop -4 * 64 N = = 5000bits ln(1 - 0.05)

  19. Open Questions • AC or DC Coupled? • In AC Coupled • What should be the Maximum overhead? • In DC coupled • What should be the Minimum overhead? • Different Guard time between different Bursts?

  20. Back up

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