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

4.2 Design Considerations

Important metrics when evaluating the performance of a repeater include isolation, selectivity, ac performance degradation, maximum gain and latency. Selectivity is easily one of the most important metrics when it comes to defining overall repeater system performance. The idea is to eliminate unwanted signals from being transmitted within the desired signals pass band of the repeater. This is crucial to reducing interference to operators in other bands. Antenna isolation is also very important because the output signal at the donor antenna can easily feedback to the service antenna, ultimately interfering with the input signal. The isolation between the donor antenna and the service antenna must be at least 30 dB. Repeaters introduce delay due to digital processing and filtering. The time for an input signal to travel from RX input to TX output is referred to as input-to-output group delay, and is usually denoted in terms of microseconds. Ideal repeaters are 100% transparent to the overall communication system, so latency must be as low as possible. Typical latency can range from 2 µs to 6 µs, depending on the architecture. Ideally, the repeated signal is an exact, amplified replica of the input signal. Poor ACPR performance, poor antenna isolation, and poor selectivity in a repeater can undesirably distort the input signal before the signal reaches the final destination. Therefore, a good repeater introduces minimum performance degradation at the input signal.