SBAS932 March   2024 DAC39RF10-SEP , DAC39RF10-SP , DAC39RFS10-SEP , DAC39RFS10-SP

PRODMIX  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 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 - DC Specifications
    6. 6.6  Electrical Characteristics - AC Specifications
    7. 6.7  Electrical Characteristics - Power Consumption
    8. 6.8  Timing Requirements
    9. 6.9  Switching Characteristics
    10. 6.10 SPI and FRI Timing Diagrams
    11. 6.11 Typical Characteristics: Bandwidth and DC Linearity
    12. 6.12 Typical Characteristics: Single Tone Spectra
    13. 6.13 Typical Characteristics: Dual Tone Spectra
    14. 6.14 Typical Characteristics: Noise Spectral Density
    15. 6.15 Typical Characteristics: Power Dissipation and Supply Currents
    16. 6.16 Typical Characteristics: Linearity Sweeps
    17. 6.17 Typical Characteristics: Modulated Waveforms
    18. 6.18 Typical Characteristics: Phase and Amplitude Noise
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagrams
    3. 7.3 Feature Description
      1. 7.3.1 DAC Output Modes
        1. 7.3.1.1 NRZ Mode
        2. 7.3.1.2 RTZ Mode
        3. 7.3.1.3 RF Mode
        4. 7.3.1.4 DES Mode
      2. 7.3.2 DAC Core
        1. 7.3.2.1 DAC Output Structure
        2. 7.3.2.2 Full-Scale Current Adjustment
      3. 7.3.3 DEM and Dither
      4. 7.3.4 Offset Adjustment
      5. 7.3.5 Clocking Subsystem
        1. 7.3.5.1 SYSREF Frequency Requirements
        2. 7.3.5.2 SYSREF Position Detector and Sampling Position Selection (SYSREF Windowing)
      6. 7.3.6 Digital Signal Processing Blocks
        1. 7.3.6.1 Digital Upconverter (DUC)
          1. 7.3.6.1.1 Interpolation Filters
          2. 7.3.6.1.2 Numerically Controlled Oscillator (NCO)
            1. 7.3.6.1.2.1 Phase-Continuous NCO Update Mode
            2. 7.3.6.1.2.2 Phase-coherent NCO Update Mode
            3. 7.3.6.1.2.3 Phase-sync NCO Update Mode
            4. 7.3.6.1.2.4 NCO Synchronization
              1. 7.3.6.1.2.4.1 JESD204C LSB Synchonization
            5. 7.3.6.1.2.5 NCO Mode Programming
          3. 7.3.6.1.3 Mixer Scaling
        2. 7.3.6.2 Channel Bonder
        3. 7.3.6.3 DES Interpolator
      7. 7.3.7 JESD204C Interface
        1. 7.3.7.1  Deviation from JESD204C Standard
        2. 7.3.7.2  Transport Layer
        3. 7.3.7.3  Scrambler and Descrambler
        4. 7.3.7.4  Link Layer
        5. 7.3.7.5  Physical Layer
        6. 7.3.7.6  Serdes PLL Control
        7. 7.3.7.7  Serdes Crossbar
        8. 7.3.7.8  Multi-Device Synchronization and Deterministic Latency
          1. 7.3.7.8.1 Programming RBD
        9. 7.3.7.9  Operation in Subclass 0 Systems
        10. 7.3.7.10 Link Reset
      8. 7.3.8 Alarm Generation
    4. 7.4 Device Functional Modes
      1. 7.4.1 DUC and DDS Modes
      2. 7.4.2 JESD204C Interface Modes
        1. 7.4.2.1 JESD204C Interface Modes
        2. 7.4.2.2 JESD204C Format Diagrams
          1. 7.4.2.2.1 16-bit Formats
          2. 7.4.2.2.2 12-bit Formats
          3. 7.4.2.2.3 8-bit Formats
      3. 7.4.3 NCO Synchronization Latency
      4. 7.4.4 Data Path Latency
    5. 7.5 Programming
      1. 7.5.1 Using the Standard SPI Interface
        1. 7.5.1.1 SCS
        2. 7.5.1.2 SCLK
        3. 7.5.1.3 SDI
        4. 7.5.1.4 SDO
        5. 7.5.1.5 Serial Interface Protocol
        6. 7.5.1.6 Streaming Mode
      2. 7.5.2 Using the Fast Reconfiguration Interface
      3. 7.5.3 SPI Register Map
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Startup Procedure for DUC/Bypass Mode
      2. 8.1.2 Startup Procedure for DDS Mode
      3. 8.1.3 Understanding Dual Edge Sampling Modes
      4. 8.1.4 Eye Scan Procedure
      5. 8.1.5 Pre/Post Cursor Analysis Procedure
      6. 8.1.6 Sleep and Disable Modes
      7. 8.1.7 Radiation Environment Recommendations
        1. 8.1.7.1 SPI Programming
        2. 8.1.7.2 JESD204C Reliability
        3. 8.1.7.3 NCO Reliability
          1. 8.1.7.3.1 NCO Frequency and Phase Correction (Strategy #1)
          2. 8.1.7.3.2 NCO Frequency Correction (Strategy No. 2)
    2. 8.2 Typical Application
      1. 8.2.1 S-Band Radar Transmitter
      2. 8.2.2 Design Requirements
      3. 8.2.3 Detailed Design Procedure
      4. 8.2.4 Detailed Clocking Subsystem Design Procedure
        1. 8.2.4.1 Example 1: SWAP-C Optimized
        2. 8.2.4.2 Example 2: Improved Phase Noise LMX2820 with External VCO
        3. 8.2.4.3 Example 3: Discrete Analog PLL for Best DAC Performance
        4. 8.2.4.4 10GHz Clock Generation
      5. 8.2.5 Application Curves
    3. 8.3 Power Supply Recommendations
      1. 8.3.1 Power Up and Down Sequence
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines and Example
  10. 9 Device and Documentation Support
    1. 9.1 Receiving Notification of Documentation Updates
    2. 9.2 Support Resources
    3. 9.3 Trademarks
    4. 9.4 Electrostatic Discharge Caution
    5. 9.5 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.4.1 Example 1: SWAP-C Optimized

The best SWAP-C sub-system leverages the high levels of integration offered by modern PLL+VCO devices, such as the LMX2820. Figure 8-7 shows a block diagram of the clocking sub-system. An external reference clock feeds the LMX2820 input, which is then used to lock the internal PLL+VCO before being fed to the output buffers. Only external passives are required to construct the loop filter and complete the sub-system system.

GUID-20230306-SS0I-CBNV-JHM1-4FT11LW67FM5-low.svg Figure 8-7 LMX2820 with Internal VCO

The LMX2820 is a flexible device and configuration can be overwhelming. For example, deciding how to decipher configure dividers, set loop filter components, and so on. A few high-level guidelines can be taken into consideration to optimize phase noise.

First,always operate the LMX2820 in integer mode when possible, as opposed to fractional mode. This implies that relationship between reference clock and output clock follows the general form:

Equation 5. FOUT = (FREF/NREF) x NDIV/NOUT

where NREF, NDIV and NOUT are the reference, feedback and output dividers respectively. FREF is the input reference frequency and FOUT is the output frequency used as the DAC clock. If this ratio cannot be found, then fractional mode must be used at the expense of degraded overall phase noise.

Second, the best in-band phase noise is achieved when the phase detector frequency is maximized and the feedback divider is minimized. The LMX2820 has a maximum phase detector frequency of 400MHz and an optional reference doubler is available for reference inputs up to 200MHz. For the same output frequency, each doubling of phase detector frequency (while halving the feedback divider) results in 3dB of in band phase noise reduction.

For an 8GHz output, use the maximum phase detector frequency of 400MHz. Set NREF = 1, NDIV = 20, and NOUT = 1 (divider bypass). For a slight degradation in in-band noise, the input can be set to 200MHz and the reference doubler is used.

Third, note that any noise on the reference input impacts close in phase noise before the in-band noise begins to dominate. In-band noise is a combination of PLL noise (phase detector, charge pump and dividers) and VCO noise, while wideband noise is limited by the noise floor of the output buffers. Close in noise is limited by the device flicker, which is independent of phase detector frequency and scales 20 x LOGbase10 with output frequency.

Finally, when operating the LMX2820 above 11GHz, the integrated output doubler must be used and this results in a sub-harmonic (that is, output frequency divided by 2) that possibly requires external filtering using either a high-pass or bandpass filter (depending on system requirements). Following the LMX2820 output with a narrow bandpass filter can also be used to suppress wideband noise.

The PLLatinumSim software is available from TI to design the external loop filter passive values.