User Guide (Version 2.2) of the
SiRad Simple® Evaluation Kit
- 18 -
Ramp time:
is reported back by the sensor. The ramp time t is calculated using the selected
sampling time t
Smp
, the number of samples n
Smp
and the clock frequency of the ADCs, like
t [us] = t
Smp
[clock cycles] * 1.04 * n
Smp
/ (36 MHz)
The sampling time t
Smp
is an internal value that is controlled by the ADC Clock Divider setting
according to Table 3. The sample frequency f
Smp
is determined by the clock frequency of the ADCs
(36 MHz) divided by the ADC sampling time t
Smp
. The constant 1.04 is an overhead correction
factor for the ramp handling.
Table 3: Sampling time and sample frequency
ADC Clock Divider ADC sampling time t
Smp
[clock cycles]
Sample frequency
[MS/s]
0
14
2.5
1
15
2.4
2
17
2.1
3
20
1.8
4
32
1.1
5
74
0.4
6
194
0.1
7
614
0.05
ADC clock divider:
sets the sampling time of the ADCs indirectly. A higher ADC clock divider means
slower sampling, according to Table 3.
Number of samples:
sets the number of samples taken per ramp.
Number of ramps
: sets the number of ramps that are driven per measurement. All ramps are
integrated to improve the SNR. Hence, higher values give slower measurements but better SNR.
However, too many ramps may smear out the signal due to the phase noise of the system.
Downsampling
: determines how many samples are averaged after sampling. Higher downsampling
values improve the accuracy but reduce the maximum range of the sensor. Voids are filled with
zeroes when downsampling. A downsampling of 0 means no downsampling, 1 means an average
of 2 values, 2 an average of 4 values, etc.
FFT size
: sets the number of FFT bins. Higher values mean better accuracy but slower calculation.
Average
: determines the number of FFTs to average. An average of 0 means 1 FFT without
averaging, 1 means an average of 2 FFTs, etc.
MTI-Mode
: activates the Moving Target Indicator mode. When activated, the sensor displays the
difference between the current measurement and the average of the previous measurements (set
by the ‘Average n’ slider).
3.2.6 Target Recognition Settings (Target Recognition Tab)
The ‘Target Recognition’ tab shown in Figure 17 is used to control the CFAR-operator for the target
recognition and the reported distance format / unit. Please also see Table 4 below for the valid
format options. The CFAR-operator is explained in Figure 18. We use a simple CACFAR-operator
that calculates the average from the reference cells for the CFAR.