Baseband and Signal Conditioning

Baseband and Signal Conditioning

The baseband stage includes LPF, PGA, and ADC,

where the beat signal is filtered, amplitude-adjusted, and digitized for further digital processing.

1. ADC and Nyquist Frequency

Since the ADC sampling rate is fixed at 2.5 MHz,

the beat frequency signal input to the ADC is expected to be limited to within the Nyquist frequency (1.25 MHz).

To ensure good signal quality and robust radar processing, i

t is recommended to keep the beat signal bandwidth within about 30% of the Nyquist frequency,

Step	Technical Description
1	The baseband bandwidth is defined by the product specifications and RF front-end signal design.
2	After the mixer, the baseband signal is conditioned by the LPF and PGA to limit the signal bandwidth, suppress out-of-band noise, and optimize the signal level before the ADC.
3	The ADC samples the conditioned baseband signal at a fixed sampling rate determined by the system (e.g., 2.5 MHz).

Step

Technical Description

1

The baseband bandwidth is defined by the product specifications and RF front-end signal design.

2

After the mixer, the baseband signal is conditioned by the LPF and PGA to limit the signal bandwidth,

suppress out-of-band noise, and optimize the signal level before the ADC.

3

The ADC samples the conditioned baseband signal at a fixed sampling rate determined by the system (e.g., 2.5 MHz).

1. Signal Flow and Processing

Step1. Given Condition

Allocated bandwidth: 200 MHz ← ISM Band 24.045 GHz ~ 24.245 GHz

Step2. Requirments by a customer

Requirement	Symbol	Typical Value	Design Impact
Max Range Limit	R_max	8 m	R_max(Requirement)→B_BB(System Limit)→T_UP(Design variables)
Range Resolution	ΔR	0.75 m	Defines the RF chirp bandwidth, B_RF = c/2ΔR
Max Velocity Limit	V_max	25 m/s	Constrains the maximum allowable chirp cycle to avoid Doppler aliasing.
Velocity Resolution	ΔV	0.25 m/s	Defines the required CPI, i.e., the number of chirps per frame

Step3. Chirp Design

Name	Symbol	Typical value	Description
RF Chirp Bandwidth	B_RF	200 MHz	Selected $B_RF=200 MHz$ within allocated band
Baseband Bandwidth	B_BB	25.4 kHz	Fixed by system bandwidth limitation (ADC/LPF).
Waveform	–	CW + SAW	Continuous-wave transmission with sawtooth FMCW chirp
Start Time	T_START	20 us	typically fixed, hardware-determined settling time
Down-chirp Time	T_DOWN	150 us	typically fixed, hardware-determined reset/return time
Stop Time	T_STOP	410 us	typically fixed, hardware-determined idle/guard time
Up-chirp Time	T_UP(min)	420 us	The actual value shall be determined by considering the frame structure.