Maximum Range vs. Chirp-up Time

Increasing chirp-up-time, T_UP allows a longer maximum measurable range by reducing the beat frequency within ADC constraints.

 

 

 

 

 

 

 

1. The relationship between chirp slope and  T_UP

The chirp slope is determined by the RF signal bandwidth and Tup,

and when B_RF is fixed, the slope increases as T_UP decreases.

 

 

 

 

 

 

2. Design Consideration

The maximum beat frequency must satisfy the ADC constraint:​

​

, B_BB is baseband signal bandwidth

 

 

 

 

 

3. Example

 

Given Conditions

Items	Parameter	Value	Remark
RF/Chirp Bandwidth	B_RF	200 MHz	Restricted by range resolution(0.75m)
ADC Sampling Rate	f_s	2.5 MHz	Fixed by system (SoC)
Nyquist Frequency	f_Nyq	1.25 MHz	Fixed by system (SoC)

 

 

Maximum Beat Frequency Limits

Margin for f_nyq	No Margin	30% Margin	98% Margin
Max Beat Frequency	1.25 MHz	0.375 MHz	25.4 kHz

 

 

T_UP Calculation for Maximum Range

Beat Frequency Max	1.25 MHz	0.375 MHz =	25.4 kHz
T_UP @ Max range 8 m	8.53 µs	28.4 µs	420 µs
T_UP @ Max range 150m	160 µs	533.3 µs	7.88 ms