Broadcom
ACPL-C740-EvalKit-UG100
7
ACPL-C740 Evaluation Kit Board
User Guide
Isolated Sigma-Delta Modulator
Figure 4: Measurement Setup
Lab bench test: Apply input voltage signal from a function generator with one shunt resistor mounted on the input of
evaluation board.
A more accurate method to measure the performance of the ACPL-C740 evaluation board is to connect a 1-shunt
resistor, then supply the voltage signal from a function generator that can drive sufficient current through the 1-shunt
resistor until an input signal level of ±200 mV is reached. One such function generator is the ultra low distortion DS360
function generator from Standford Research Systems.
shows the SNR/SNDR performance using this method.
If such a function generator is not available, it is best to connect an actual shunt resistor and connect to the current-sensing
system directly.
Table 3: SNR/SNDR Performance
Filter
Configuration
Signal Source from Audio Jack of Laptop
Signal Freq. = 500 Hz
Signal Freq. = 1000 Hz
Signal Freq. = 2000 Hz
SNR(dB)
SNDR(dB)
SNR(dB)
SNDR(dB)
SNR(dB)
SNDR(dB)
Sinc3 DR = 64
not enough sampling sinewave cycles
75
72
72
71
Sinc3 DR = 128
81
77
79
76
79
76
Sinc3 DR = 256
82
78
82
78
81
77
