Polyphase filter for MM-wave frequencies featuring symmetric layout
A two-stage, passive, RC polyphase filter for mm-wave quadrature LO generation is presented. The filter features an innovative, symmetrical layout structure, which is more robust to parasitics than the conventional layout. Layout parasitics which become important at mm-wave frequencies are identified and a compensated. Impedance variations and transfer functions are evaluated considering these dominant parasitics. More than 15 dB improvement in image rejection ratio is achieved in comparison with conventional layouts. Using the inventive techniques more than 35 dB of image rejection ratio over a bandwidth of 6 GHz is demonstrated in an outphasing transmitter at 60 GHz in 40 nm CMOS.
1. A passive, quadrature, RC polyphase filter (PPF) stage operative at Extremely High Frequencies (EHF), comprising:
a first input, to which a negative In-phase signal is connected;
a second input, to which a positive In-phase signal is connected;
a third input, to which a positive Quadrature signal is connected;
a fourth input, to which a negative Quadrature signal is connected;
first, second, third, and fourth outputs corresponding to the respective first, second, third, and fourth inputs;
a resistor interposed between each respective input and output;
a first capacitor coupled between the first input and second output;
a second capacitor coupled between the second input and fourth output;
a third capacitor coupled between the third input and first output;
a fourth capacitor coupled between the fourth input and third output;
wherein a conductor connecting the second input to the second capacitor has a substantially equal length to another conductor connecting the third input to the third capacitor; and
wherein respective conductors connecting the first, second, third, and fourth capacitors to the respective output thereof all have a substantially equal length.
2. A two-stage, passive, quadrature, RC polyphase filter (PPF) operative at Extremely High Frequencies (EHF), comprising first and second PPF stages according to claim 1 connected in series, wherein each of the first, second, third, and fourth outputs of the first stage are connected to the corresponding first, second, third, and fourth inputs of the second stage.
3. The two-stage PPF of claim 2 , further comprising a constant amplitude input feed connected to the first, second, third, and fourth inputs of the first PPF stage.
4. The two-stage PPF of claim 2 , further comprising a constant phase input feed connected to the first, second, third, and fourth inputs of the first PPF stage.
5. The two-stage PPF of claim 2 , wherein each of the second and third capacitors connected to the second and third inputs of the respective first and second stages have a capacitance C n , and each of the first and fourth capacitors connected to the first and fourth inputs of the respective first and second stages have a capacitance C, wherein the two-stage PPF is L-compensated for an inductive parasitic effect by the capacitances C n of each stage having a value related to the capacitances C of each stage given by
1
sC
=
1
sC
n
+
sL
where L is a parasitic inductance of metallization conductors connecting the C n capacitances to the second and third inputs of each stage.
6. The two-stage PPF of claim 2 wherein the two-stage PPF is operative to generate mm-wave quadrature signals for a 60 GHz outphasing transmitter.
7. The PPF stage of claim 1 , further comprising a constant phase input feed connected to the first, second, third, and fourth inputs.
8. The PPF stage of claim 1 , wherein the second and third capacitors connected to the second and third inputs have a capacitance C n , and the first and fourth capacitors connected to the first and fourth inputs have a capacitance C, wherein the PPF stage is L-compensated for an inductive parasitic effect by the capacitances C n having a value related to the capacitances C given by
1
sC
=
1
sC
n
+
sL
where L is a parasitic inductance of the respective conductors connecting the C n capacitances to the second and third inputs.
9. The PPF stage of claim 1 wherein each of the resistors comprise salicided p+ resistors.
10. The PPF stage of claim 1 wherein the first, second, third, and fourth capacitors comprise metal-oxide-metal capacitors.
11. The PPF stage of claim 1 , further comprising a constant amplitude input feed connected to the first, second, third, and fourth inputs.
12. A passive, quadrature, RC polyphase filter (PPF) stage operative at Extremely High Frequencies (EHF), comprising:
a first input, to which a negative Quadrature signal is connected;
a second input, to which a negative In-phase signal is connected;
a third input, to which a positive In-phase signal is connected;
a fourth input, to which a positive Quadrature signal is connected;
first, second, third, and fourth outputs corresponding to the respective first, second, third, and fourth inputs;
a resistor interposed between each respective input and output;
a first capacitor coupled between the first input and second output;
a second capacitor coupled between the second input and fourth output;
a third capacitor coupled between the third input and first output;
a fourth capacitor coupled between the fourth input and third output;
wherein a conductor connecting the second input to the second capacitor has a substantially equal length to another conductor connecting the third input to the third capacitor; and
wherein respective conductors connecting the first, second, third, and fourth capacitors to the respective output thereof all have a substantially equal length.
13. A two-stage, passive, quadrature, RC polyphase filter (PPF) operative at Extremely High Frequencies (EHF), comprising first and second PPF stages according to claim 12 connected in series, wherein each of the first, second, third, and fourth outputs of the first stage are connected to the corresponding first, second, third, and fourth inputs of the second stage.
14. The two-stage PPF of claim 13 , further comprising a constant amplitude input feed connected to the first, second, third, and fourth inputs of the first PPF stage.
15. The two-stage PPF of claim 13 , further comprising a constant phase input feed.
16. The two-stage PPF of claim 13 , wherein each of the second and third capacitors connected to the second and third inputs of the respective first and second stages have a capacitance C n , and each of the first and fourth capacitors connected to the first and fourth inputs of the respective first and second stages have a capacitance C, wherein the two-stage PPF is L-compensated for an inductive parasitic effect by the capacitances C n each stage having a value related to the capacitances C of each stage given by
1
sC
=
1
sC
n
+
sL
where L is a parasitic inductance of metallization conductors connecting the C n capacitances to the second and third inputs of each stage.
17. The two-stage PPF of claim 13 wherein the two-stage PPF is operative to generate mm-wave quadrature signals for a 60 GHz outphasing transmitter.
18. The PPF stage of claim 12 , further comprising a constant phase input feed connected to the first, second, third, and fourth inputs.
19. The PPF stage of claim 12 , wherein the second and third capacitors connected to the second and third inputs have a capacitance C n , and the first and fourth capacitors connected to the first and fourth inputs have a capacitance C, wherein the PPF stage is L-compensated for an inductive parasitic effect by the capacitances C n having a value related to the capacitances C given by
1
sC
=
1
sC
n
+
sL
where L is a parasitic inductance of the respective conductors connecting the C n capacitances to the second and third inputs.
20. The PPF stage of claim 12 wherein each of the resistors comprise salicided p+ resistors.
21. The PPF stage of claim 12 wherein the first, second, third, and fourth capacitors comprise metal-oxide-metal capacitors.
22. The PPF stage of claim 12 , further comprising a constant amplitude input feed connected to the first, second, third, and fourth inputs.
23. A passive, quadrature, RC polyphase filter (PPF) stage operative at Extremely High Frequencies (EHF), comprising:
a first input, to which a positive Quadrature signal is connected;
a second input, to which a negative Quadrature signal is connected;
a third input, to which a negative In-phase signal is connected;
a fourth input, to which a positive In-phase signal is connected;
first, second, third, and fourth outputs corresponding to the respective first, second, third, and fourth inputs;
a resistor interposed between each respective input and output;
a first capacitor coupled between the first input and second output;
a second capacitor coupled between the second input and fourth output;
a third capacitor coupled between the third input and first output;
a fourth capacitor coupled between the fourth input and third output;
wherein a conductor connecting the second input to the second capacitor has a substantially equal length to another conductor connecting the third input to the third capacitor; and
wherein respective conductors connecting the first, second, third, and fourth capacitors to the respective output thereof all have a substantially equal length.
24. A two-stage, passive, quadrature, RC polyphase filter (PPF) operative at Extremely High Frequencies (EHF), comprising first and second PPF stages according to claim 23 connected in series, wherein each of the first, second, third, and fourth outputs of the first stage are connected to the corresponding first, second, third, and fourth inputs of the second stage.
25. The two-stage PPF of claim 24 , further comprising a constant amplitude input feed connected to the first, second, third, and fourth inputs of the first PPF stage.
26. The two-stage PPF of claim 24 , further comprising a constant phase input feed.
27. The two-stage PPF of claim 24 , wherein each of the second and third capacitors connected to the second and third inputs of the respective first and second stages have a capacitance C n , and each of the first and fourth capacitors connected to the first and fourth inputs of the respective first and second stages have a capacitance C, wherein the two-stage PPF is L-compensated for an inductive parasitic effect by the capacitances C n each stage having a value related to the capacitances C of each stage given by
1
sC
=
1
sC
n
+
sL
where L is a parasitic inductance of metallization conductors connecting the C n capacitances to the second and third inputs of each stage.
28. The two-stage PPF of claim 24 wherein the two-stage PPF is operative to generate mm-wave quadrature signals for a 60 GHz outphasing transmitter.
29. The PPF stage of claim 23 , further comprising a constant phase input feed connected to the first, second, third, and fourth inputs.
30. The PPF stage of claim 23 , wherein the second and third capacitors connected to the second and third inputs have a capacitance C n , and the first and fourth capacitors connected to the first and fourth inputs have a capacitance C, wherein the PPF stage is L-compensated for an inductive parasitic effect by the capacitances C n having a value related to the capacitances C given by
1
sC
=
1
sC
n
+
sL
where L is a parasitic inductance of the respective conductors connecting the C n capacitances to the second and third inputs.
31. The PPF stage of claim 23 wherein each of the resistors comprise salicided p+ resistors.
32. The PPF stage of claim 23 wherein the first, second, third, and fourth capacitors comprise metal-oxide-metal capacitors.
33. The PPF stage of claim 23 , further comprising a constant amplitude input feed connected to the first, second, third, and fourth inputs.