SLAA871 January   2019 AFE7422 , AFE7444

 

  1.   AFE74xx as a single-chip wideband repeater using loopback mode
    1.     Trademarks
    2. 1 Introduction
    3. 2 Repeater Mode (RX-TX Loopback With SerDes Bypassed)
      1. 2.1 Overview of the AFE74xx Repeater Mode
      2. 2.2 Configuration of the AFE74xx as a Repeater
      3. 2.3 Programming the Repeater Mode
        1. 2.3.1 Hardware Setup
        2. 2.3.2 Software Setup and GUI Configuration
    4. 3 130-MHz Digital Repeater System Overview
      1. 3.1 Key System Specifications
    5. 4 System Overview
      1. 4.1 Block Diagram
      2. 4.2 Design Considerations
      3. 4.3 Highlighted Products
        1. 4.3.1 LMK04828
      4. 4.4 System Design Theory
    6. 5 Hardware and Testing
      1. 5.1 Measured Latency and Gain
        1. 5.1.1 Hardware
        2. 5.1.2 Test Setup and Results
      2. 5.2 Measured Linearity Performance
        1. 5.2.1 Hardware and Test Setup
        2. 5.2.2 Test Results
      3. 5.3 Measured Selectivity (Out-of-Band Jammer)
        1. 5.3.1 Hardware and Test Setup
        2. 5.3.2 Test Results
    7. 6 Terminology

2.3.2 Software Setup and GUI Configuration

Programming the AFE74xx EVM in repeater mode is simple. After the AFE74xxEVM is programmed normally in a desired mode, a configuration file containing a specific sequence of register writes required to enable repeater mode must then be loaded to the device through the Low Level View tab in the AFE74xx GUI. The mode used to program the AFE74xx must have the same LMFSK values for both RX and TX. Table 1 shows the sequence of register writes that must be loaded to the AFE74xx EVM in order to enable repeater mode (RX-TX loopback mode).

NOTE

The configuration file containing the following register writes is provided in the AFE7444 product folder. Save the file titled loopback_mode_enable.cfg.

Table 1. Register Sequence for Repeater Mode (RX-TX Loopback)

Process
(W for Write)		 Address
(Hex)		 Register Value
(Hex)		 Comment
W 0x10 0x55 Open txducp0 page for all TX
W 0x7E 0x1F Set RBD register (0x7E) to hex value of 64 / F – 1.
For example:
LMFSHd = 44210, F= 2, RBD value is 64 / 2 – 1 = 31.
Hex value for 31 = 0x1F.
Therefore, register 0x7E is programmed to 0x1F.
W 0x10 0x00 Close txducp0 page for all TX
W 0x11 0x8 Select TRAFFICCNTL page
W 0xC5 0x5 RX-TX loop-back enabled for both 2T2R_TOPs
W 0xCF 0x1 Loopback FIFO init_state set
W 0x11 0x0 Close TRAFFICCNTL page
W 0x17 0x0 Select SerDes_JESD_TX page
W 0x45 0xC0 RX init_state clear
W 0x45 0x80 FB init_state clear
W 0x45 0x0 FIFO inti_state clear
W 0x26 0x0 RX jesd_clear_data clear
W 0x17 0x0 Close SerDes_JESD_TX page
W 0x11 0x3 Select TXDIG_P0 page
W 0x20 0x0 TX init_state clear for both TX_TOPs
W 0x11 0x0 Close TXDIG_P0 page
W 0x11 0x8 Select TRAFFICCNTL page
W 0x1A0 0xFC Gate SYSREF
W 0x11 0x0 Close TRAFFICCNTL page
If sync out is not looped back to sync in, use the following SPI programming to establish SYNC
W 0x17 0xC Select SerDes_JESD_TX page
W 0x72 0xFF Override STX output with K28.5
Delay 100 ms
W 0x72 0xF0 Override STX output with K28.5
W 0x17 0x0 Close SerDes_JESD_TX page

The following steps show how to bring up the AFE74xx EVM and then enable repeater mode. In this example, the AFE74xx is programmed in mode 4 and then a config file enabling repeater is loaded in the Low Level View tab. For more details on how to bring up the AFE74xx EVM, reference the AFE74xxEVM user's guide. After the AFE74xx is powered up, launch the AFE74xx GUI, and then reference the following steps:

  1. Click the EVM Selection button, and verify that the proper EVM is selected, as shown in Figure 2.
    2. slaa871-evm-selection.gifFigure 2. EVM Selection
  2. Click the Clock Selection button, and select Internal PLL, as shown in Figure 3.
    3. slaa871-clock-selection.gifFigure 3. Clock Selection
  3. Click the DAC Frequency Selection button, and select a DAC clock frequency of 8847.36 MHz, as shown in Figure 4.
    4. slaa871-dac-frequency-selection.gifFigure 4. DAC Frequency Selection
  4. Click the ADC Frequency Selection button, and choose a DIV factor of 3 to program the ADC clock to 2949.12 MHz, as shown in Figure 5.
    5. slaa871-adc-frequency-selection.gifFigure 5. ADC Frequency Selection
  5. As shown in Figure 6, click the AFE Mode Selection button, and select Mode 4.
  6. Click Set Mode.
  7. Click Run Complete Startup Sequence to program the AFE.
    8. slaa871-mode-selection-and-program.gifFigure 6. AFE Mode Selection
  8. Select the Advanced tab, and click on the SYSREF continuous mode (SYSREF Cont. M) button shown in a red box in Figure 7.
    9. slaa871-continuous-sysref.gifFigure 7. Advanced Tab
  9. In the Low Level View tab, click on the open folder icon, as shown in Figure 8.
  10. Load the loopback_mode_enable.cfg config file that was saved previously.
    11. slaa871-low-level-view.gifFigure 8. Low Level View Tab
  11. At this point, the input signal should be visible on the DAC A output. If the output is not visible, verify that register 0x7E is set to the correct RBD value for your configuration. The RBD value depends on the F value in the AFE74xx JESD configuration mode. The RBD should be set RBD register (0x7E) to a hex value of 64 / F – 1. For example, in mode 4, LMFSHd = 44210. where F= 2. Therefore, the RBD value is 64 / 2 – 1 = 31. The hex value for 31 = 0x1F. Therefore, register 0x7E is programmed to 0x1F.
  12. After the looped back input tone is verified, go back to the Advanced tab and adjust the RX and TX NCO values as desired, as shown in the red box of Figure 9. After the desired NCO frequency is entered, click the RX NCO Update or TX NCO Update button. The RX NCO downconverts the input signal to a digital baseband frequency. The baseband signal is upconverted to the frequency set by the TX RF NCO value. For example, the current RX NCO and TX NCO values are both set to 1700 MHz. If the input signal applied to the AFE74xxEVM is 1750 MHz, then the RX NCO downconverts the signal to a baseband frequency of 50 MHz. Then, the TX NCO upconverts the baseband signal to 1750 MHz.
    13. slaa871-rx-tx-nco-values.gifFigure 9. Adust RX and TX NCO Values to Desired Frequencies