For an analog second-order Sigma-Delta modulation class-D power amplifier circuit, the continuous domain mathematical model and discrete time domain iterative mathematical model are constructed. For the power amplifier circuit, the continuous domain mathematical model is derived, which shows that the principle of the second order sigma-delta modulation circuit is self-excited oscillation based on positive feedback, so as to realize the output switching signal. Since the continuous domain mathematical model can only obtain the self-excited oscillation frequency, the continuous domain mathematical model is discretized to obtain the discrete time domain iterative mathematical model. This model can calculate the switching frequency value of any input signal and analyze the stability conditions of second-order Sigma-Delta modulation circuit. The experimental results show that the error between the theoretical switching frequency calculated based on the mathematical model and the experimental value is less than 14%, which verifies the correctness of the mathematical model.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |