SBASAP4 April   2025 ADC3664-EP , ADC3664-SEP

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics - Power Consumption
    6. 5.6 Electrical Characteristics - DC Specifications
    7. 5.7 Electrical Characteristics - AC Specifications
    8. 5.8 Timing Requirements
    9. 5.9 Typical Characteristics
  7. 6 Parameter Measurement Information
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Analog Input
        1. 7.3.1.1 Analog Input Bandwidth
        2. 7.3.1.2 Analog Front End Design
          1. 7.3.1.2.1 Sampling Glitch Filter Design
          2. 7.3.1.2.2 Analog Input Termination and DC Bias
            1. 7.3.1.2.2.1 AC-Coupling
            2. 7.3.1.2.2.2 DC-Coupling
      2. 7.3.2 Clock Input
        1. 7.3.2.1 Single Ended vs Differential Clock Input
      3. 7.3.3 Voltage Reference
        1. 7.3.3.1 Internal voltage reference
        2. 7.3.3.2 External voltage reference (VREF)
        3. 7.3.3.3 External voltage reference with internal buffer (REFBUF/CTRL)
      4. 7.3.4 Digital Down Converter
        1. 7.3.4.1 DDC MUX
        2. 7.3.4.2 Digital Filter Operation
        3. 7.3.4.3 FS/4 Mixing with Real Output
        4. 7.3.4.4 Numerically Controlled Oscillator (NCO) and Digital Mixer
        5. 7.3.4.5 Decimation Filter
        6. 7.3.4.6 SYNC
        7. 7.3.4.7 Output Formatting with Decimation
      5. 7.3.5 Digital Interface
        1. 7.3.5.1 Output Formatter
        2. 7.3.5.2 Output Bit Mapper
          1. 7.3.5.2.1 2-Wire Mode
          2. 7.3.5.2.2 1-Wire Mode
          3. 7.3.5.2.3 ½-Wire Mode
        3. 7.3.5.3 Output Interface and Mode Configuration
          1. 7.3.5.3.1 Configuration Example
        4. 7.3.5.4 Output Data Format
      6. 7.3.6 Test Pattern
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal operation
      2. 7.4.2 Power Down Options
    5. 7.5 Programming
      1. 7.5.1 Configuration using PINs only
      2. 7.5.2 Configuration using the SPI interface
        1. 7.5.2.1 Register Write
        2. 7.5.2.2 Register Read
  9. 8 Application Information Disclaimer
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Input Signal Path
        2. 8.2.2.2 Sampling Clock
        3. 8.2.2.3 Voltage Reference
      3. 8.2.3 Application Curves
    3. 8.3 Initialization Set Up
      1. 8.3.1 Register Initialization During Operation
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
      2. 8.5.2 Layout Example
  10. 9 Register Maps
    1. 9.1 Detailed Register Description
  11. 10Device and Documentation Support
    1. 10.1 Receiving Notification of Documentation Updates
    2. 10.2 Support Resources
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information
    1. 12.1 Mechanical Data

7.3.4.4 Numerically Controlled Oscillator (NCO) and Digital Mixer

The decimation block is equipped with a 32-bit NCO and a digital mixer to fine tune the frequency placement prior to the digital filtering. The oscillator generates a complex exponential sequence of:

ejωn (default) or e–jωn

where: frequency (ω) is specified as a signed number by the 32-bit register setting

The complex exponential sequence is multiplied with the real input from the ADC to mix the desired carrier to a frequency equal to fIN + fNCO. The NCO frequency is tuned from –FS/2 to +FS/2 and is processed as a signed, 2s complement number. After programming a new NCO frequency, the MIXER RESTART register bit or SYNC pin has to be toggled for the new frequency to get active. Additionally, the ADC3664-xEP provides the option via SPI to invert the mixer phase.

The NCO frequency setting is set by the 32-bit register value given and calculated as:

Equation 1. NCO frequency = 0 to + FS/2: NCO = fNCO × 232 / FS
Equation 2. NCO frequency = -FS/2 to 0: NCO = (fNCO + FS) × 232 / FS

where:

  • NCO = NCO register setting (decimal value)
  • fNCO = Desired NCO frequency (MHz)
  • FS = ADC sampling rate (MSPS)

The NCO programming is further illustrated with this example:

  • ADC sampling rate FS = 125MSPS
  • Input signal fIN = 10MHz
  • Desired output frequency fOUT = 0MHz

For this example, there are actually four ways to program the NCO and achieve the desired output frequency as shown in Table 7-1.

Table 7-1 NCO value calculations example
Alias or negative imagefNCONCO ValueMixer PhaseFrequency translation for fOUT
fIN = –10MHzfNCO = 10MHz343597384as isfOUT = fIN + fNCO = –10MHz +10MHz = 0MHz
fIN = 10MHzfNCO = –10MHz4638564680fOUT = fIN + fNCO = 10MHz + (–10MHz) = 0MHz
fIN = 10MHzfNCO = 10MHz343597384invertedfOUT = fIN– fNCO = 10MHz – 10MHz = 0MHz
fIN = –10MHzfNCO = –10MHz4638564680fOUT = fIN– fNCO = –10MHz – (–10MHz) = 0MHz