SLYT836 March   2023 IWR6443 , IWR6843 , IWR6843AOP

 

  1. 1 Introduction
  2. 2 The importance of integration
  3. 3 FMCW
  4. 4 Chirps
  5. 5 Mixer
  6. 6 FFT and peak detection
  7. 7 Beamsteering, in the direction that you want to sense
  8. 8 Calibration
  9. 9 Conclusion
  10. 10Related Websites

4 Chirps

Chirps describe the modulation used in FMCW; the instantaneous frequency f(t) varies linearly with time, so this is a linear frequency chirp. The frequency difference between the transmitted chirp and the received chirp is directly proportional to the time of flight (the time to reach the target and come back), and thus the distance to the target.

Equation 1 expresses the transmitted wave amplitude as:

Equation 1. y T t = A T × sin ⁡ 2 π × f 0 + K × t × t

where K is the slope by which the transmitted frequency increases by unit of time (for the IWR6843, this value can be anything between 0 and 250 MHz/µs), AT is the amplitude at which the signal transmits (transmit power), and f0 is the lowest frequency transmitted at the beginning of the chirp (57 GHz or 60 GHz, depending on the selected VCO).

Equation 2 expresses the received wave amplitude as:

Equation 2. y R t = A R × s i n ( 2 × π × f 0 + K × t - δ × ( t - δ ) )

where, for δ = 2 × d v (which is twice the time of flight), d is the distance to the target, and v is the celerity of the light in the medium.