| 摘要 |
An analogue to digital conversion unit ( 208, 210 ) comprises three analogue to digital converters (ADCs) ( 300, 301, 302 ) having different dynamic ranges. A lowest dynamic range ADC ( 300 ) and middle dynamic range ADC ( 301 ) have saturation detectors SAT for outputting a signal when the amplitude of an input analogue signal reaches their respective dynamic ranges and saturates them. The middle dynamic range ADC ( 301 ) and highest dynamic range ADC have enable inputs EN for switching themselves on. The output of the saturation detector SAT of the lowest dynamic range ADC ( 300 ) is connected to the enable input EN of the middle dynamic range ADC ( 301 ). The output of the saturation detector SAT of the middle dynamic range ADC ( 301 ) is connected to the enable input EN of the highest dynamic range ADC ( 302 ). So, whilst the middle and the highest dynamic range ADCs ( 301, 302 ) are normally switched off, when the lowest dynamic range ADC becomes saturated, the middle dynamic range ADC ( 301 ) is switched on; and when the middle dynamic range ADC ( 301 ) is saturated, the highest dynamic range ADC ( 302 ) is switched on. The input analogue signal is therefore converted to a digital output using the ADC ( 300, 301, 302 ) having the lowest sufficient dynamic range and the higher dynamic range ADCs ( 301, 302 ) are switched off unless needed.
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