ZHCSN12B December   2020  – October 2022 ADC3681 , ADC3682 , ADC3683

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information
    5. 6.5  Electrical Characteristics - Power Consumption
    6. 6.6  Electrical Characteristics - DC Specifications
    7. 6.7  Electrical Characteristics - AC Specifications
    8. 6.8  Timing Requirements
    9. 6.9  Typical Characteristics - ADC3681
    10. 6.10 Typical Characteristics - ADC3682
    11. 6.11 Typical Characteristics - ADC3683
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Analog Input
        1. 8.3.1.1 Analog Input Bandwidth
        2. 8.3.1.2 Analog Front End Design
          1. 8.3.1.2.1 Sampling Glitch Filter Design
          2. 8.3.1.2.2 Analog Input Termination and DC Bias
            1. 8.3.1.2.2.1 AC-Coupling
            2. 8.3.1.2.2.2 DC-Coupling
        3. 8.3.1.3 Auto-Zero Feature
      2. 8.3.2 Clock Input
        1. 8.3.2.1 Single Ended vs Differential Clock Input
        2. 8.3.2.2 Signal Acquisition Time Adjust
      3. 8.3.3 Voltage Reference
        1. 8.3.3.1 Internal voltage reference
        2. 8.3.3.2 External voltage reference (VREF)
        3. 8.3.3.3 External voltage reference with internal buffer (REFBUF)
      4. 8.3.4 Digital Down Converter
        1. 8.3.4.1 DDC MUX
        2. 8.3.4.2 Digital Filter Operation
        3. 8.3.4.3 FS/4 Mixing with Real Output
        4. 8.3.4.4 Numerically Controlled Oscillator (NCO) and Digital Mixer
        5. 8.3.4.5 Decimation Filter
        6. 8.3.4.6 SYNC
        7. 8.3.4.7 Output Formatting with Decimation
      5. 8.3.5 Digital Interface
        1. 8.3.5.1 Output Formatter
        2. 8.3.5.2 Output Scrambler
        3. 8.3.5.3 Output Bit Mapper
        4. 8.3.5.4 Output Interface/Mode Configuration
          1. 8.3.5.4.1 Configuration Example
        5. 8.3.5.5 Output Data Format
      6. 8.3.6 Test Pattern
    4. 8.4 Device Functional Modes
      1. 8.4.1 Normal Operation
      2. 8.4.2 Power Down Options
      3. 8.4.3 Digital Channel Averaging
    5. 8.5 Programming
      1. 8.5.1 Configuration using PINs only
      2. 8.5.2 Configuration using the SPI interface
        1. 8.5.2.1 Register Write
        2. 8.5.2.2 Register Read
    6. 8.6 Register Map
      1. 8.6.1 Detailed Register Description
  9. 9 Application Information Disclaimer
    1. 9.1 Typical Application
      1. 9.1.1 Design Requirements
      2. 9.1.2 Detailed Design Procedure
        1. 9.1.2.1 Input Signal Path
        2. 9.1.2.2 Sampling Clock
        3. 9.1.2.3 Voltage Reference
      3. 9.1.3 Application Curves
    2. 9.2 Initialization Set Up
      1. 9.2.1 Register Initialization During Operation
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 接收文档更新通知
    2. 10.2 支持资源
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 术语表
  11. 11Mechanical, Packaging, and Orderable Information

9.1.1 Design Requirements

Frequency domain applications cover a wide range of frequencies from low input frequencies at or near DC in the 1st Nyquist zone to undersampling in higher Nyquist zones. If very low input frequency is supported then the input has to be DC coupled and the ADC driven by a fully differential amplifier (FDA). If low frequency support is not needed then AC coupling and use of a balun may be more suitable.

The internal reference is used since DC precision is not needed. However the ADC AC performance is highly dependent on the quality of the external clock source. If in-band interferers can be present then the ADC SFDR performance will be a key care about as well. A higher ADC sampling rate is desirable in order to relax the external anti-aliasing filter – an internal decimation filter can be used to reduce the digital output rate afterwards.

Table 9-1 Design key care-abouts
FEATUREDESCRIPTION
Signal BandwidthDC to 20 MHz
Input DriverSingle ended to differential signal conversion and DC coupling
Clock SourceExternal clock with low jitter

When designing the amplifier/filter driving circuit, the ADC input full-scale voltage needs to be taken into consideration. For example, the ADC368x input full-scale is 3.2 Vpp. When factoring in ~ 1 dB for insertion loss of the filter, then the amplifier needs to deliver close to 3.6 Vpp. The amplifier distortion performance will degrade with a larger output swing and considering the ADC common mode input voltage the amplifier may not be able to deliver the full swing. The ADC368x provides an output common mode voltage of 0.95V and the THS4541 for example can only swing within 250 mV of its negative supply. A unipolar 3.3 V amplifier power supply will thus limit the maximum voltage swing to ~ 2.8 Vpp. Hence if a larger output swing is required (factoring in filter insertion loss) then a negative supply for the amplifier is needed in order to eliminate that limitation. Additionally input voltage protection diodes may be needed to protect the ADC from over-voltage events.

Table 9-2 Output voltage swing of THS4541 vs power supply
DEVICEMIN OUTPUT VOLTAGEMAX SWING WITH 3.3 V/ 0 V SUPPLYMAX SWING WITH 3.3 V/ -1.0 V SUPPLY
THS4541VS- + 250 mV2.8 Vpp6.8 Vpp
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