Systems and methods for synchronous demodulation
Systems and methods for synchronous demodulation using passive sampled analog filtering are disclosed. A system for synchronous demodulation includes an input channel for accepting an input signal, a first passive sampled analog filter for filtering the input signal, a mixer for mixing the filtered input signal and outputting a mixed signal, a second passive sampled analog filter for filtering the mixed signal, and an output channel for outputting the filtered mixed signal.
1. A system for synchronous demodulation using passive sampled analog filtering, comprising:
an input channel for receiving an input signal;
a first passive sampled analog filter for sampling and filtering the input signal;
a mixer for mixing the filtered input signal from the first filter and outputting a mixed signal;
a second passive sampled analog filter for filtering the mixed signal; and
an output channel for outputting the filtered mixed signal.
2. The system of claim 1 , wherein the first filter and the mixer are combined in a single passive circuit block.
3. The system of claim 1 , further comprising a first active amplifier between the first filter and the mixer for amplifying the filtered signal.
4. The system of claim 3 , further comprising a second active amplifier between the mixer and the second filter for amplifying the mixed signal.
5. The system of claim 1 , wherein the first passive sampled analog filter is a programmable filter.
6. The system of claim 1 , wherein the first passive sampled analog filter is one of a low-pass filter, a band-pass filter, a high-pass filter, and a filter with an arbitrary filter shape.
7. The system of claim 1 , wherein the first passive analog filter is one of a FIR filter and an IIR filter.
8. The system of claim 1 , wherein the second passive sampled analog filter is a low pass filter.
9. The system of claim 1 , further comprising a clock generator for generating an excitation signal, and wherein the excitation signal is modified by a target element, and the modified excitation signal is the input signal.
10. The system of claim 9 , wherein the target element is a body part and wherein the system measures bioimpedance of the body part.
11. The system of claim 9 , wherein the clock generator generates a reference signal, and wherein the reference signal is mixed with the filtered input signal at the mixer.
12. The system of claim 9 , wherein the target element is one of a sensor and a transformer.
13. A method for synchronous demodulation using passive sampled analog filtering, comprising:
presenting an excitation signal to a target element;
receiving, at an input, a modified signal from the target element;
sampling and filtering, using a passive sampled analog filter, the modified signal to remove noise;
mixing the filtered signal with a reference signal from a clock generator;
filtering, using a second passive sampled analog filter, the mixed signal; and
outputting, from the second passive sampled analog filter, a signal representing characteristics of the target element.
14. The method of claim 13 , wherein presenting the excitation signal includes presenting a current to the target element, and wherein receiving a modified signal includes receiving a voltage.
15. The method of claim 13 , wherein presenting the excitation signal includes presenting a voltage to the target element, and wherein receiving a modified signal includes receiving a current.
16. The method of claim 13 , wherein outputting the signal includes outputting an I-component of the signal and outputting a Q-component of the signal.
17. A synchronous demodulation system using passive sampled analog filtering, comprising:
a clock generator for generating an excitation signal;
an input channel for receiving a modified excitation signal;
means for passively sampling, filtering and mixing the modified excitation signal to synchronously demodulate the modified excitation signal and generate a demodulated output signal.
18. The system of claim 17 , wherein the means for passively filtering the modified excitation signal includes a passive sampled analog filter.
19. The system of claim 18 , wherein the passive sampled analog filter is one of a low-pass filter, a band-pass filter, a high-pass filter, and a filter with an arbitrary filter shape.
20. The system of claim 17 , wherein the means for mixing the modified excitation signal include a mixer, and wherein the mixer is one of a two-level mixer, a three-level mixer, and a mixer with greater than three levels.