Down Sampling

Check the baseband signal bandwidth at the ADC input such that it is oversampled by the fixed ADC sampling rate.
The signal is oversampled at the ADC stage using a fixed sampling rate higher than the Nyquist rate.
Apply decimation in the down-sampling block based on the oversampled data while avoiding aliasing.

 

 

Glossary	Symbol	Description
Signal Bandwidth		Refer to §Waveform-Chirp page
Nyquist Rate		The Nyquist rate is the minimum sampling rate without aliasing,
Nyquist Frequency		Frequency components above this limit will cause aliasing.

 

 

When down sampling, care must be taken to prevent aliasing,

as aliasing degrades Range FFT performance, including SNR, peak distortion, and range accuracy.

Oversampling vs. Decimation Without Aliasing

 

 

 

1. Signal Flow and Processing

Apply decimation in the down-sampling block based on the oversampled data while avoiding aliasing.

 

 

 

 

 

 

2. Example Cases

For data sampled at 2.5 MHz, the allowable decimation factors

that prevent aliasing for each baseband bandwidth (B_BB) are summarized in the table below.

 

If Baseband Signal Bandwidth	Allowed Decimation Options	Effective Fs after Decimation (MHz)
B_BB ≤ 1.25 MHz	1:1	2.5
B_BB ≤ 0.625 MHz	1:1, 1:2	2.5, 1.25
B_BB ≤ 0.3125 MHz	1:1, 1:2, 1:4	2.5, 1.25, 0.625
B_BB ≤ 0.15625 MHz	1:1, 1:2, 1:4, 1:8	2.5, 1.25, 0.625, 0.3125

 

 

 

 

 

3. Example Report of Radar Sensor SoC

 

Type	Field Name	Dword	Bit Range	설명
Header	Fixed Pattern	Dword 0	[31:24]	1010 1010
Header	Reserved	Dword 0	[23]	0
Header	Fixed Pattern	Dword 0	[22:20]	10
Header	RAW_chirp_cnt	Dword 0	[19:11]	Frame 내 chirp 순번 (0부터 시작)
Header	RAW_DATA_cnt	Dword 0	[10:0]	DS RAW 데이터 개수 m
Data	RAW_real_data[0]	Dword 1	[31:16]	DS RAW real part (signed)
Data	RAW_imag_data[0]	Dword 1	[15:0]	DS RAW imaginary part (signed)
Data	RAW_real_data[1]	Dword 2	[31:16]	DS RAW real part (signed)
Data	RAW_imag_data[1]	Dword 2	[15:0]	DS RAW imaginary part (signed)
Data	RAW_real_data[n]	Dword …	[31:16]	DS RAW real part (signed)
Data	RAW_imag_data[n]	Dword …	[15:0]	DS RAW imaginary part (signed)
Data	RAW_real_data[m-1]	Dword m	[31:16]	DS RAW real part (signed)
Data	RAW_imag_data[m-1]	Dword m	[15:0]	DS RAW imaginary part (signed)
Tail	Check_sum	Dword m+1	[31:16]	해당 frame 데이터 합 (low 16bit sum 결과)
Tail	RAW_FRAME_INDEX	Dword m+1	[15:12]	Frame counter (0부터 시작)
Tail	Reserved	Dword m+1	[11:10]	0
Tail	CFG_MSG	Dword m+1	[9:8]	User defined bits
Tail	Fixed Pattern	Dword m+1	[7:0]	0101 0101