A 10 bit_100 MHz CMOS Analog-to-Digital Converter by ert554898


									A 10 bit,100 MHz CMOS Analog-
       to-Digital Converter

High Speed A/D Converter Architectures
Proposed A/D Converter Architecture
Circuit Design and Simulations
Prototype Chip Test Results
Research Plan
    Applications of High Speed High
      Resolution A/D Converter

High frequency digital data communication
Waveform acquisition instruments
Medical Imaging
Video Signal Processing
Increasing DSP complexity in
  communications systems
High Resolution High Speed CMOS
         A/D Converters
Fully Parallel(Flash) A/D Converter
               Conceptually most straightforward
                 1. Highest possible speed
                2. Resolution: 8-10bits
               Disadvantages
                 1. 2 comparators requires
                   So, Hardware complexity grows
                   exponentially with resolution
                2. Large power dissipation and
                   input capacitance
         Two-Step A/D Converter

 Less hardware complexity than Flash type
 Digital error correction is possible
 Disadvantages:
    Requires inter-stage amplifier
     (longer conversion time)
    Requires multiple clocks per conversion
Multi-Stage Pipeline A/D Converter

   Well-suited to CMOS, as residue amplifier has built-in S/H
   May repeat same blocks in cascade
   Approximately linear hardware cost with resolution
   Limitations:
    1. Residue amplifier settling is speed bottleneck
    2. Linearity determined by input S/H and residue formation
      Parallel Pipelined A/D Converter

 Conversion rate increases with the number of channels
 Input S/H must acquire singal at full Nyquist bandwidth
 Performance ultimately limited by:
  1. Timing skews and jitter between channels
  2. Mismatch in gain, offset and full scale between channels
Effect of Sampling Timing Offset in Parallel
          Pipelined A/D Converter
SNR with gain mismatch 2 channel
         pipeline ADC
              Design Specification
   10 bit resolution
   100 MHz conversion rate
   Fully Differential Implementation
   1.0V input full scale
   1.0m n-well CMOS technology with linear capacitance option
   1.0 W power dissipation
   2-channel 3-stage pipelined architecture
   4 bit/stage conversion
   Parallel Pipeline Switch Cap. Residue Amplifier
   Resistor Ladder DAC
   On-chip clock buffer
Detail Block Diagram of
Timing Diagram of S/H, 4-bit
      ADDA, and RA
    Schematic of Non-resetting S/H

 Equivalent to two resetting S/H
 Following stage can obtain the valid data for full period(10ns)
 Disadvantage:
    Ch and Cd increase a time constant
Simulated Dynamic Performance
            of S/H
4-bit AD-DA Block Diagram
               Residue Amplifier

 Gain of 2 Residue Amplifier:
   Generate a residue (subtract DAC output from S/H output)
   Reduce inter-channel offect  Offset Cancellation Scheme
 Gain of 4 Residue Amplifier:
   Reduce inter-channel offset  Offset Cancellation Scheme
   Compensation capacitor added ot stabilized loop when
Digital Circuit in ADC
Clock Generation Circuit
Measured SNDR,THD,and SFDR at
         500 KHz input
Measured Signal / (Noise+Distortion)
 at 4, 50 & 95 MHz Sampling rate
Power Dissipation

         Total power dissipation
         = 1.1W @ 95MS/s
Floor Plan of A/D Converter

                 Layout Design Issues:
                   Clock distribution
                   Reduce the Offset in
                     Residue Amplifier
Summary of A/D Characteristics

10-bit resolution
95MS/s conversion rate
1m n-well CMOS technology with linear capacitor
Spurious tones are less -65db after simple on chip
 offset cancellation
1.2W power dissipation @ single 5V
Digital error correction
First 10-bit, 100MS/s CMOS ADC
                 Research Plan

Investigate further effects of architecture on SFDR
Hope to design 14bit linear input S/H capable of
 2.5MHz or higher clock rate
   Nonlinearity in interstage of ADC
    (For example: Offset, Gain, Carpacitor and
     Resistor mismatch, Timing mismatch ..)

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