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EECS 270C

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EECS 270C

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    1. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 1 Electrical-to-Optical Interfaces (1)

    2. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 2 Electrical-to-Optical Interfaces (2)

    3. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 3 Electrical-to-Optical Interfaces (3) Since were not modulating the signal itself, but the phase shift, much faster bit rates are possible.Since were not modulating the signal itself, but the phase shift, much faster bit rates are possible.

    4. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 4 Electrical-to-Optical Interfaces (4)

    5. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 5 Electrical-to-Optical Interfaces (5) IB is servod so that LD bias current IB = Vref/RIB is servod so that LD bias current IB = Vref/R

    6. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 6 Optical Receiver Block Diagram Optical signal can have varying amplitude; gain of O-E converter is fixed. Thus limiting amplifier is required to deliver constant amplitude to input of EQ/CDR. EQ often required to compensate for distortion from the channel. (Will discuss shortly.)Optical signal can have varying amplitude; gain of O-E converter is fixed. Thus limiting amplifier is required to deliver constant amplitude to input of EQ/CDR. EQ often required to compensate for distortion from the channel. (Will discuss shortly.)

    7. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 7 Optical-to-Electrical Interfaces (1)

    8. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 8 Optical-to-Electrical Interfaces (2)

    9. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 9 Transimpedance Amplifier (TIA)

    10. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 10 Transimpedance Amplifier (2) Cg is input capacitance of op-amp. Would prefer to have feedback pole as high as possible.Cg is input capacitance of op-amp. Would prefer to have feedback pole as high as possible.

    11. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 11 Transimpedance Amplifier (3) All of the above sensitivity requirements All of the above sensitivity requirements

    12. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 12 Transimpedance Amplifier (4) (Pause here.)(Pause here.)

    13. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 13 Limiting Amplifiers

    14. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 14 7-Stage Limiting Amplifier Example (1)

    15. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 15 7-Stage Limiting Amplifier Example (2)

    16. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 16 7-Stage Limiting Amplifier Example (3)

    17. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 17 Limiting Amplifier Offset Compensation

    18. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 18 Equalization/Compensation of Transmission Media

    19. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 19 Copper Cable Model Draw impulse response on the board. Emphasize that energy needs to be added mainly up to 5GHz to restore the signal.Draw impulse response on the board. Emphasize that energy needs to be added mainly up to 5GHz to restore the signal.

    20. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 20 Effect of Copper on Broadband Data

    21. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 21 Adaptive Analog Equalizer for Copper Will demonstrate a case studyWill demonstrate a case study

    22. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 22 Equalizer Block Diagram 5GHz peaked amplifier will restore high frequencies near baud rate that are lost in copper cable. (Assuming monotonically decreasing cable characteristic) With more equalization required, 5 GHz is more emphasized. 5GHz peaked amplifier will restore high frequencies near baud rate that are lost in copper cable. (Assuming monotonically decreasing cable characteristic) With more equalization required, 5 GHz is more emphasized.

    23. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 23 Analog Equalizer Concept (1)

    24. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 24 Analog Equalizer Concept (2) Note V1 has widely varying pulse width (down to 0), but not the case for V2. Weighted sum will give some dc component as well as increase pulse width.Note V1 has widely varying pulse width (down to 0), but not the case for V2. Weighted sum will give some dc component as well as increase pulse width.

    25. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 25 Analog Equalizer Concept (3)

    26. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 26 Feedforward Path

    27. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 27 Equalizer Frequency Response This figure shows the simulated ac response for 3 different values of Vcontrol. The upper curve coresponds to a lower Vcontrol. We have noted that the equalization setting primarily affects the low frequency gainThis figure shows the simulated ac response for 3 different values of Vcontrol. The upper curve coresponds to a lower Vcontrol. We have noted that the equalization setting primarily affects the low frequency gain

    28. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 28 ISI & Transition Time This confirms the theoretical study shown earlier.This confirms the theoretical study shown earlier.

    29. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 29 Slicer This slicer is implemented by two cascaded CML buffers. The first buffer ehibits fast transition time and corrects the signal amplitude. This limiting is critical because the equalizer output exhibits large over shoots even when the ISI is minimized. The second buffer produces an output with a fixed transition time that optimize the output ISI. This optimal transition time is achieved when the obseved output exhibits the lowest ISI. Possible questions: how did you find the optimal rise fall time? How can you tell for difference cable?This slicer is implemented by two cascaded CML buffers. The first buffer ehibits fast transition time and corrects the signal amplitude. This limiting is critical because the equalizer output exhibits large over shoots even when the ISI is minimized. The second buffer produces an output with a fixed transition time that optimize the output ISI. This optimal transition time is achieved when the obseved output exhibits the lowest ISI. Possible questions: how did you find the optimal rise fall time? How can you tell for difference cable?

    30. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 30 Feedback Path The feedback path is shown here where you can see the two detectors are designed to give an output pulse whose engergy is proportional to the input transition time. The pulses are then applied to the differential inputs of an integrator. The integrator output resonds to the difference of the transition time between the detector inputs. When the adaptive loop reaches steady state, v control will be set such that the equalizer output will exhibit the same transition time as the slicer output. The feedback path is shown here where you can see the two detectors are designed to give an output pulse whose engergy is proportional to the input transition time. The pulses are then applied to the differential inputs of an integrator. The integrator output resonds to the difference of the transition time between the detector inputs. When the adaptive loop reaches steady state, v control will be set such that the equalizer output will exhibit the same transition time as the slicer output.

    31. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 31 Transition Time Detector

    32. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 32 Integrator The integraor , designed using standard CMOS techniques, gives an output control voltage Vcontrol that is proportional to the energy in the pulsesat the output of the detectors. This voltage is the fed back to the equalizer. A common mode feedback is designed to improve the stability. The transfer function of the integrator can be approximated as: where. The integraor , designed using standard CMOS techniques, gives an output control voltage Vcontrol that is proportional to the energy in the pulsesat the output of the detectors. This voltage is the fed back to the equalizer. A common mode feedback is designed to improve the stability. The transfer function of the integrator can be approximated as: where.

    33. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 33 Detector + Integrator

    34. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 34 System Analysis This analyzes the overall dynamics of the adaptation loop. It depends on the characteristic of each component.This analyzes the overall dynamics of the adaptation loop. It depends on the characteristic of each component.

    35. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 35 Measurement Setup

    36. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 36 Measured Eye Diagrams

    37. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 37 Summary of Measured Performance This table is the summary of measured performance. (read the table) This table is the summary of measured performance. (read the table)

    38. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 38 Equalization vs. Compensation The previous example showed an analog equalizer. This is used for only well-behaved channel characteristics. Well now consider methods for Electronic Dispersion Compensation (EDC), which works on a bigger set of channel characteristics. (Will use term equalization even in compensation systems.)The previous example showed an analog equalizer. This is used for only well-behaved channel characteristics. Well now consider methods for Electronic Dispersion Compensation (EDC), which works on a bigger set of channel characteristics. (Will use term equalization even in compensation systems.)

    39. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 39 Pre-Cursor/Post-Cursor ISI For this exercise well consider a single-ended pulse (baseline at 0).For this exercise well consider a single-ended pulse (baseline at 0).

    40. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 40 Feedforward Equalization (FFE) To cancel other pre- or post-cursor ISI, we can have more delays and subtractions. In general, we need the same number of weighted sums as there are sampling points to make zero.To cancel other pre- or post-cursor ISI, we can have more delays and subtractions. In general, we need the same number of weighted sums as there are sampling points to make zero.

    41. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 41 Feedforward Equalization (2) This is consistent with intuition that such an equalizer would be HPF. Note low-frequency gain < 1.This is consistent with intuition that such an equalizer would be HPF. Note low-frequency gain < 1.

    42. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 42 Feedforward Equalization (3) Post-cursor distortion can be cancelled by setting cursor in the middle instead of far left.Post-cursor distortion can be cancelled by setting cursor in the middle instead of far left.

    43. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 43 Feedforward Equalization (4) For well-behaved channels, coefficients usually alternate in sign. If not, we would need a more elaborate structure. Delay elements are set by CML circuit with unity gain and set delay. (Will show example later.)For well-behaved channels, coefficients usually alternate in sign. If not, we would need a more elaborate structure. Delay elements are set by CML circuit with unity gain and set delay. (Will show example later.)

    44. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 44 Feedforward Equalization (5) Equalization at higher frequencies can be accomplished with fractional spacing -- that is, delays that are less than 1UI. Result is sharper rise & fall times. Eye diagram correspond to LPF channel + FFE.Equalization at higher frequencies can be accomplished with fractional spacing -- that is, delays that are less than 1UI. Result is sharper rise & fall times. Eye diagram correspond to LPF channel + FFE.

    45. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 45 Adaptation (1) Will talk about how error is generated shortly. Dout_hat corresponds to an appropriate delay that comes from the channel and assignment of which tap is the cursor.Will talk about how error is generated shortly. Dout_hat corresponds to an appropriate delay that comes from the channel and assignment of which tap is the cursor.

    46. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 46 Adaptation (2) In LMS we instead use the immediate value of e rather than its average. For sufficiently small step size, on average, the correction should move in the correct direction of decreasing e^2. In the realization of LMS, each tap requires a multiplication and summation (or integration).In LMS we instead use the immediate value of e rather than its average. For sufficiently small step size, on average, the correction should move in the correct direction of decreasing e^2.In the realization of LMS, each tap requires a multiplication and summation (or integration).

    47. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 47 Adaptation (3) Blind adaptation is preferable, especially considering slowly varying changes in channel characteristic. This was already shown in the analog equalizer example earlier.Blind adaptation is preferable, especially considering slowly varying changes in channel characteristic. This was already shown in the analog equalizer example earlier.

    48. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 48 Adaptation (4)

    49. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 49 Decision Feedback Equalization (DFE) Resembles the FFE but flipped horizontally and vertically. Resembles the FFE but flipped horizontally and vertically.

    50. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 50 Decision Feedback Equalization (2)

    51. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 51 Decision Feedback Equalization (3)

    52. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 52 FFE + DFE

    53. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 53 Front-End Circuits for DSP-Based Receivers

    54. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 54 PGA Design

    55. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 55 PGA Example (1)

    56. EECS 270C / Spring 2008 Prof. M. Green / UC Irvine 56 PGA Example (2)

    57. Track & Hold Circuit

    58. Simulation Results

    59. High-speed Comparator

    60. Comparator/Latch Results (1)

    61. Metastable Behavior (1)

    62. Metastable Behavior (2)

    63. Metastable Behavior (3)

    64. Metastable Behavior (4)

    65. Reducing Metastability Errors

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