Apparatus comprising frequency selective circuit and method
Various embodiments are disclosed relating to techniques of filtering and down-converting a received signal. In accordance with an example embodiment of the present invention, an analog signal may be received and amplified in a transconductance amplifier. The amplified signal may be connected to a switching arrangement and an impedance circuit connected in series, and frequency down-converted in a second circuit. The resulting analog base band signal may be fed back to a base band input between the switching arrangement and the impedance circuit.
1. An apparatus, comprising
a frequency selective circuit with at least one resonator stages, a frequency down converting stage and having an analog signal as an input, wherein the at least one resonator stage is realized with an impedance transferring circuit comprising:
a transconductance amplifier, and
a switching arrangement and an impedance circuit connected in series, the switching arrangement being configured to switch the impedance of the impedance circuit from base band to the frequency of the input signal and
a base band input between the switching arrangement and the impedance circuit, configured to receive an analog feedback signal from the output of the frequency selective circuit.
2. The apparatus of claim 1 , wherein the frequency down converting stage is realized with another impedance transferring circuit comprising:
another transconductance amplifier; and
another switching arrangement and another impedance circuit connected in series, the other switching arrangement being configured to frequency down convert the input signal; and
a base band output between the other switching arrangement and the other impedance circuit.
3. The apparatus of claim 2 , wherein the frequency selective circuit comprises:
an A/D converter, configured to receive the base band output signal and to produce one or more digital 1-bit or multibit signals as the output signal of the frequency selective circuit, and
a D/A converter configured to convert the output signal of the frequency selective circuit to the analog feedback signal.
4. The apparatus of claim 3 , comprising an active Miller integrator connected between the base band output and the A/D converter input.
5. The apparatus of claim 3 , wherein the D/A converter is configured to provide a FIR filter function and comprises:
at least one delay line, and
at least two 1-bit D/A converters.
6. The apparatus of claim 1 , wherein the frequency down converting stage comprises a quadrature down converting mixer.
7. The apparatus of claim 1 , wherein the impedance transferring circuit of the at least one resonator stage is configured to integrate and frequency up convert the analog feedback signal, and add the resulting signal to the input signal before the frequency down converting of the input signal.
8. The apparatus of claim 1 , wherein the frequency selective circuit comprises a delta sigma modulator.
9. A method, comprising:
receiving an analog signal as an input;
processing the analog signal in at least one circuit by amplifying the signal in a transconductance amplifier,
connecting the amplified signal to a switching arrangement and an impedance circuit connected in series,
switching by the switching arrangement the impedance of the impedance circuit from base band to the frequency of the input signal;
connecting the amplified signal to a second circuit;
down mixing the signal to base band by the second circuit and obtaining a base band output signal;
connecting the base band output signal to a feedback loop and obtaining an analog base band feedback signal; and
receiving by a base band input between the switching arrangement and the impedance circuit the analog base band feedback signal from the feedback loop.
10. The method of claim 9 , further comprising:
upconverting the feedback signal to a frequency in the frequency range of the input signal.
11. The method of claim 9 , further comprising:
filtering the base band output signal with an active Miller integrator.
12. The method of claim 9 , further comprising:
performing an A/D conversion to the base band output signal of the second circuit and obtaining one or more digital signals.
13. The method of claim 12 , further comprising:
converting the one or more digital signals into an analog output signal; and
connecting the analog output signal to the feedback loop and obtaining the analog base band feedback signal.
14. The method of claim 12 , further comprising:
performing comb filtering to the one or more digital signals; and
converting the one or more comb filtered signals into an analog output signal; and
connecting the analog output signal to the feedback loop and obtaining the analog base band feedback signal.
15. The method of claim 9 , further comprising:
performing delta sigma modulation to the base band output signal of the second circuit and obtaining one or more digital signals.