I am designing a frequency modulated continuous wave radar sensor module, I want to know as the level of IF signal is low at output, what level of amplification would be required to analyse the output by a microcontroller later.
Frequency Modulated Continuous Wave Radar based sensor module
radar
Related Solutions
The receiver's output is not the red line. Instead, it is the beat frequency between red line and blue line. f(beat) = f(blue)-f(red) = fb;
The receiver calculates fb, which is the center frequency shown in FFT diagram. Knowing fb, you can calculate R from the formula $$R=c*Ts*Fb/2Bsweep $$
Check out slide page 9. The diagram you posted indicates the condition when the detected object does not move. What may happen if the object moves? If the detected moves relative to receiver, doplar effect will start to work. Therefore you have a different frequency, which is doplar frequency.
Check the bottom diagram of slide page 9, it shows the condition when the object move: combination of doplar effect and previous frequency shift.
- I guess you may need to know one point. The transmitter is keeping sweeping the frequency, which is indicated by the blue line. In the diagram in page 9, the frequency increases and then decreases and keep doing that in cycles. As a result, beat frequency has the pattern shown. You can get both distance and speed from the beat frequency.
Assuming your receiver is a "homodyne architecture (mix TX and RX together)" as stated by mkeith, the two methods (sawtooth vs triangular) will be identical assuming your scene is stationary during the measurement period. The low-pass filtered mixer output will then always be proportional to the range of the scatterers, regardless of a up or down sweep. With a I/Q receiver you should be able to distinguish between a negative and positive beat, but I can't see any benefit. Only generating a up-sweep (sawtooth) will most likely be easier to implement, but that depends entirely on the hardware.
For moving targets, we need to distinguish between 2 cases.
- Slow moving targets
- Fast moving targets
where 'fast' and 'slow' is relative to the sweep-time. For a sufficiently slow moving target, the doppler shift will be negligible and you can approximate it as stationary. You can find the velocity of a slow moving object by comparing the data from multiple sweeps, again the triangular vs sawtooth makes no difference.
I belive the intention of the triangular waveform is that you can now solve the ambiguity caused by a fast-moving object. In a FMCW radar, a moving target may seem indistinguishable from a stationary one. One traditional then introduces the triangular waveform to solve this ambiguity, see e.g. this open access article, especially figure 1.
Note that this only works for a single moving target, when you have multiple moving targets stuff gets more complicated so thread carefully.
In summary: In choosing between the two waveforms, there is a special case with a fast moving object where the triangular waveform may aid in extracting velocity (or should I say: radial relative velocity between the radar and reflector) depending on the velocity and chirp-rate. But for all other cases, the distinction is mute.
I hope that helped, let me know if I should clarify any of the points.
Best Answer
Gain = Output/Input, so you need an amplifier with a gain of (whatever microcontroller needs)/"low" = a big amount.
In other words, some numbers are needed to determine a useful gain. If you don't want the amplifier to clip, then you have to work out the gain based on the maximum input peak. If you don't mind clipping, then you can use the smallest peak that you expect to see and amplify it to the maximum value acceptable to the microcontroller to set the gain.
Clipping or saturation is undesirable if you are handling an analogue waveform into an ADC that you need to preserve the relative values of the sample. However, if you are only looking for edges for timing purposes, as long as the amplifier doesn't introduce extra edges when it clips, it would be acceptable.