Synchronization in fmcw radar systems

Abstract

The disclosure provides a radar apparatus for estimating a position and a velocity of the plurality of obstacles. The radar apparatus includes a local oscillator that generates a first signal. A first transmit unit receives the first signal from the local oscillator and generates a first transmit signal. A frequency shifter receives the first signal from the local oscillator and generates a second signal. A second transmit unit receives the second signal and generates a second transmit signal. The frequency shifter provides a frequency offset to the first signal based on a routing delay mismatch to generate the second signal such that the first transmit signal is phase coherent with the second transmit signal.

What is claimed is: 
     
         1 . A radar apparatus comprising
 a local oscillator configured to generate a first signal;   a first transmit unit configured to receive the first signal from the local oscillator and configured to generate a first transmit signal,   a frequency shifter configured to receive the first signal from the local oscillator and configured to generate a second signal; and   a second transmit unit configured to receive the second signal and configured to generate a second transmit signal, wherein the frequency shifter is configured to provide a frequency offset to the first signal based on a routing delay mismatch to generate the second signal such that the first transmit signal is phase coherent with the second transmit signal.   
     
     
         2 . The radar apparatus of  claim 1 , wherein the frequency shifter comprises:
 a function generator configured to receive a frequency offset value and generates a digital signal;   a digital to analog converter (DAC) coupled to the function generator and configured to generate an analog signal corresponding to the digital signal, and   a mixer configured to multiply the analog signal and the first signal to generate the second signal.   
     
     
         3 . The radar apparatus of  claim 1 , wherein the first transmit unit comprises:
 a first power amplifier coupled to the local oscillator and configured to amplify the first signal to generate the first transmit signal; and   a first transmit antenna unit coupled to the first power amplifier and configured to transmit the first transmit signal received from the first power amplifier.   
     
     
         4 . The radar apparatus of  claim 1 , wherein the second transmit unit comprises:
 a second power amplifier coupled to the frequency shifter and configured to amplify the second signal to generate the second transmit signal; and   a second transmit antenna unit coupled to the second power amplifier and configured to transmit the second transmit signal received from the second power amplifier.   
     
     
         5 . The radar apparatus of  claim 1 , wherein the routing delay mismatch is estimated from a routing delay from the local oscillator to the first transmit antenna unit, and from a routing delay from the local oscillator to the second transmit antenna unit. 
     
     
         6 . The radar apparatus of  claim 1 , wherein the first transmit signal and the second transmit signal are scattered by a plurality of obstacles to generate a scattered signal. 
     
     
         7 . The radar apparatus of  claim 1  further comprising a receive unit, the receive unit comprising:
 a receive antenna unit configured to receive the scattered signal; 
 a low-noise amplifier (LNA) coupled to the receive antenna unit and configured to amplify the scattered signal to generate an amplified scattered signal; 
 a mixer coupled to the LNA and the local oscillator, the mixer configured to mix the amplified scattered signal and the first signal to generate an IF (intermediate frequency) signal; 
 an ADC (analog to digital converter) coupled to the mixer and configured to sample the IF signal to generate a sampled data; and 
 a processor coupled to the ADC and configured to estimate a position and a velocity of the plurality of obstacles from the sampled data. 
 
     
     
         8 . The radar apparatus of  claim 1 , wherein the first signal is a ramp segment having a start frequency and a fixed slope. 
     
     
         9 . The radar apparatus of  claim 8 , wherein the frequency offset is estimated from at least one of the routing delay mismatch and the fixed slope. 
     
     
         10 . A method comprising:
 generating a first signal;   generating a first transmit signal from a first signal;   provide a frequency offset to the first signal based on a routing delay mismatch to generate a second signal; and   generating a second transmit signal from the second signal, wherein the first transmit signal is phase coherent with the second transmit signal.   
     
     
         11 . The method of  claim 10  further comprising estimating the routing delay mismatch from a time difference between a time instant when the first signal is generated and a time instant when the first transmit signal is transmitted, and from a time difference between the time instant when the first signal is generated and a time instant when the second transmit signal is transmitted. 
     
     
         12 . The method of  claim 10  further comprising amplifying the first signal to generate the first transmit signal, and amplifying the second signal to generate the second transmit signal. 
     
     
         13 . The method of  claim 10  further comprising scattering of the first transmit signal and the second transmit signal by a plurality of obstacles to generate a scattered signal. 
     
     
         14 . The method of  claim 10  further comprising:
 amplifying the scattered signal to generate an amplified scattered signal; 
 mixing the amplified scattered signal and the first signal to generate an IF (intermediate frequency) signal; 
 sampling the IF signal to generate a sampled data, and 
 estimating a position and a velocity of the plurality of obstacles from the sampled data. 
 
     
     
         15 . The method of  claim 10 , wherein the first signal is a ramp segment having a start frequency and a fixed slope. 
     
     
         16 . The method of  claim 15  further comprising estimating the frequency offset from at least one of the routing delay mismatch and the fixed slope.