Polyphase filter (PPF) including RC-LR sections
Polyphase filters (PPFs) can be used to generate quadrature or other phase-shifted representations of an input signal provided to the PPF. In one approach, a “passive” polyphase filter can include a combination of resistive and capacitive elements. Such a topology can be referred to as an RC-PPF topology. Another passive circuit topology can be used to provide a PPF, by replacing the resistive elements with inductive elements, and by replacing the capacitive elements with resistive elements. A filter circuit can include cascaded RC-PPF and LR-PPF sections, such as in an alternating manner (e.g., an “RC-LR” topology). In this approach, a total insertion loss of cascaded LR-PPF and RC-PPF sections can be reduced as compared to using LR-PPF or RC-PPF sections, alone.
1. An electronic circuit defining an analog filter circuit, the electronic circuit comprising:
at least two cascaded polyphase filter sections, the at least two cascaded polyphase filter sections comprising:
a first polyphase filter section type including resistive elements and first reactive elements comprising a first type of reactive device; and
a second polyphase filter section type electrically coupled in series with the first polyphase filter section type, the second polyphase filter type including resistive elements and second reactive elements comprising a different second type of reactive device;
an input port coupled to the at least two cascaded polyphase filter sections; and
at least two output ports coupled to the at least two cascaded polyphase filter sections, wherein the at least two cascaded polyphase filter sections are arranged to provide, at the at least two output ports, respective phase-shifted representations of an input signal provided to the input port;
wherein the first type of reactive device or the second type of reactive device comprises a transmission line segment.
2. The electronic circuit of claim 1 , wherein the first type of reactive device comprises a capacitor; and
wherein the second type of reactive device comprises the transmission line segment.
3. The electronic circuit of claim 1 , wherein the first type of reactive device comprises a transmission line segment; and
wherein the second type of reactive device comprises a capacitor.
4. The electronic circuit of claim 1 , wherein the input port is coupled to the at least two cascaded polyphase filter sections through a third filter section; and
wherein the at least two output ports are coupled to the at least two cascaded polyphase filter sections through a fourth filter section.
5. The electronic circuit of claim 4 , comprising a signal source coupled to the input port; and
wherein the at least two output ports comprise an in-phase output, and a quadrature output that is phase-shifted 90 degrees with respect to the in-phase output.
6. The electronic circuit of claim 1 , wherein the at least two output ports comprise respective differential output ports.
7. The electronic circuit of claim 6 , wherein the respective differential output ports comprise:
a first differential port having a first node to provide a first representation of the input signal and a second node to provide a 180-degree phase-shifted representation of the first representation; and
a second differential port having a first node to provide a 90-degree phase-shifted representation of the first representation and a second node to provide 270-degree phase-shifted representation of the first representation.
8. The electronic circuit of claim 1 , comprising four cascaded polyphase filter sections including alternating serially-coupled sections comprising the first polyphase filter section type and the second polyphase filter section type.
9. The electronic circuit of claim 1 , wherein the transmission line segment comprises an integrated circuit transmission line segment.
10. An electronic circuit for providing phase-shifted representations of an input signal, the electronic circuit comprising:
a filter circuit comprising cascaded polyphase filter sections including alternating serially-coupled sections comprising a first polyphase filter section type and a second polyphase filter section type, the first polyphase filter section type comprising first reactive elements comprising a first type of reactive device, and the second polyphase filter section type comprising second reactive elements comprising a different second type of reactive device; and
a signal source coupled to an input port of the filter circuit;
wherein the filter circuit defines at least two output ports to provide respective phase-shifted representations of a signal generated by the signal source;
wherein the first type of reactive device or the second type of reactive device comprises a transmission line segment.
11. The electronic circuit of claim 10 , wherein the first reactive elements comprise capacitors; and
wherein the second reactive elements comprise transmission line segments.
12. The electronic circuit of claim 10 , wherein the first reactive elements comprise transmission line segments; and
wherein the second reactive elements comprise capacitors.
13. The electronic circuit of claim 11 , wherein the transmission line segments comprise integrated circuit transmission line segments.
14. The electronic circuit of claim 10 , wherein the cascaded polyphase filter sections and the signal source are co-integrated within a commonly-shared integrated circuit package.
15. The electronic circuit of claim 10 , wherein the at least two outputs ports comprise respective differential output ports, comprising:
a first differential output port having a first node to provide an first representation of the input signal and a second node to provide a 180-degree phase-shifted representation of the first representation; and
a second differential output port having a first node to provide a 90-degree phase-shifter representation of the first representation and a second node to provide 270-degree phase-shifted representation of the first representation.
16. A method for providing phase-shifted representations of an input signal, comprising:
receiving an input signal at an input port defined by a filter circuit;
generating phase-shifted representations of the input signal using the filter circuit, wherein the filter circuit comprises cascaded polyphase filter sections including alternating serially-coupled sections comprising a first polyphase filter section type and the second polyphase filter section type, the first polyphase filter section type comprising first reactive elements comprising a first type of reactive device, and the second polyphase filter section type comprising second reactive elements comprising a different second type of reactive device;
wherein the first type of reactive device or the second type of reactive device comprises a transmission line segment.
17. The method of claim 16 , wherein the first reactive elements comprise capacitors; and
wherein the second reactive elements comprise transmission line segments.
18. The method of claim 16 , wherein the first reactive elements comprise transmission line segments; and
wherein the second reactive elements comprise capacitors.
19. The method of claim 16 , wherein the input signal is generated by a signal source coupled to the input port.
20. The method of claim 16 , wherein the phase-shifted representations comprise a first differential representation of the input signal and a quadrature differential representation.