Loop filter for a continuous time sigma delta analog to digital converter
View Patent ↗A loop filter for a continuous time sigma delta analog to digital converter which converts an analog input signal into a digital output signal, said loop filter comprising an active analog filter which includes active devices for providing a power gain, wherein the number of active devices is lower than the filter order of said active analog filter.
1. A loop filter for a continuous time sigma delta analog to digital converter which converts an analog input signal into a digital output signal, the loop filter comprising:
an input having an input signal, the input signal at least in part representative of the digital output signal of the sigma delta analog to digital converter;
an active analog filter operably coupled to the input, the active analog filter including a first number of active devices for providing a power gain, the active analog filter being of an Nth order, wherein N exceeds the first number of active devices.
2. The loop filter according to claim 1 ,
wherein at least one of said active devices comprises an operational amplifier.
3. The loop filter according to claim 1 ,
wherein at least one of said active devices comprises a transconductance amplifier.
4. The loop filter according to claim 1 ,
wherein at least one of said active device comprises a voltage to current converter.
5. The loop filter according to claim 1 , wherein said active analog filter comprises a plurality of series connected cascaded analog filter elements.
6. The loop filter according to claim 5 ,
wherein said cascaded analog filter elements comprise cascaded biquad filter elements.
7. The loop filter according to claim 6 ,
wherein said cascaded analog filter elements comprise cascaded lattice filter elements.
8. The loop filter according to claim 6 ,
wherein at least one biquad filter element is a Sallen-and-Key filter element.
9. The loop filter according to claim 1 ,
wherein the active analog filter includes at least one Sallen-and-Key filter element.
10. The loop filter according to claim 1 ,
further comprising an output terminal operably connected to provide a loop filter output signal to a quantizer which quantizes the loop filter output signal to generate said digital output signal.
11. The loop filter according to claim 10 ,
wherein the analog active filter comprises a third order filter and the first number of active devices is two.
12. The loop filter according to claim 1 ,
wherein said loop filter comprises at least one digital-analog-converter (DAC) operable to receive the digital output signal and generate an analog signal based thereon.
13. The loop filter according to claim 12 ,
wherein the input signal comprises the analog signal generated by the DAC added to the analog input signal.
14. A sigma delta analog-digital-converter which converts an analog input signal to a digital output signal,
comprising:
a loop filter which comprises an active analog filter, the active analog filter that includes a first number of active devices providing a power gain, the first number of active devices lower than a filter order of said active analog filter; and
a quantizer which quantizes a loop filter output signal of said active loop filter to generate said digital output signal.
15. The sigma delta analog-digital-converter according to claim 14 , wherein said loop filter includes a first input terminal for applying said analog input signal.
16. The sigma delta analog-digital-converter according to claim 15 , wherein the loop filter further comprises a second input terminal configured to receive the digital output signal of said quantizer.
17. The sigma delta analog-digital-converter according to claim 16 , wherein said loop filter comprises at least one digital-analog-converter operably coupled to convert the digital output signal received at said second input terminal of said loop filter into an analog signal.
18. The sigma delta analog-digital-converter according to claim 17 , wherein the analog signal generated by said digital-analog-converter is added to the analog input signal applied to said first input terminal of said loop filter.
19. The loop filter according to claim 14 ,
wherein the active analog filter includes at least one biquad filter element.
20. The loop filter according to claim 19 ,
wherein said at least one biquad filter element is a Sallen-and-Key filter element.