Constant impedance filter
View Patent ↗A method and apparatus to provide a bi-directional constant impedance filter. Embodiments include electric networks which give filter responses while presenting a constant impedance to a signal received at either an input or an output port for a plurality of frequencies.
1. An apparatus comprising:
a first bi-directional constant impedance filter, wherein the bi-directional constant impedance filter comprises:
a first port coupled to one of a source or a load having a first impedance, wherein the first port is configured to constantly present the first impedance to a signal received at the first port for a plurality of frequencies; and
a second port coupled to the other of the source or the load having the first impedance, wherein the second port is configured to constantly present the first impedance to a signal received at the second port for a plurality of frequencies; and
a second bi-directional constant impedance filter coupled in series with the first bi-directional constant impedance filter to form a filter structure, wherein the first and second bi-directional constant impedance filters are non-interacting and wherein the filter structure presents the first impedance to a signal received at an input and at an output.
2. The apparatus of claim 1 , further comprising:
a third bi-directional constant impedance filter coupled in series with the first and second bi-directional constant impedance filters to form a second filter structure, wherein the first, second and third bi-directional constant impedance filters are non-interacting and wherein the second filter structure presents the first impedance to a signal received at an input and at an output.
3. The apparatus of claim 1 , wherein the first bi-directional constant impedance filter comprises a low pass filter.
4. The apparatus of claim 3 , wherein the low pass filter comprises a pi form filter, a tee form filter or a bridged-tee form filter.
5. The apparatus of claim 4 , wherein the bridged-tee form filter comprises:
a first inductor coupled between a first node and a second node;
a first resistor coupled between the first node and a third node;
a first capacitor coupled between the third node and a fourth node; and
a second resistor coupled between the second node and the third node.
6. The apparatus of claim 5 , wherein the bridged-tee form filter further comprises:
a third resistor coupled between the fourth node and a fifth node;
a fourth resistor coupled between the fourth node and a sixth node; and
a second inductor coupled between the fifth node and the sixth node.
7. The apparatus of claim 1 , wherein the bi-directional constant impedance filter comprises a pole/zero filter.
8. The apparatus of claim 7 , wherein the pole/zero filter comprises a pi form filter, a tee form filter or a bridged-tee form filter.
9. The apparatus of claim 1 , wherein the bi-directional constant impedance filter comprises a high pass filter.
10. The apparatus of claim 9 , wherein the high pass filter comprises a pi form filter, a tee form filter or a bridged-tee form filter.
11. The apparatus of claim 1 , wherein the bi-directional constant impedance filter comprises a zero/pole filter.
12. The apparatus of claim 11 , wherein the zero/pole filter comprises a pi form filter, a tee form filter or a bridged-tee form filter.
13. The apparatus of claim 1 , wherein the bi-directional constant impedance filter comprises a bandreject filter.
14. The apparatus of claim 13 , wherein the bandreject filter comprises a pi form filter, a tee form filter or a bridged-tee form filter.
15. The apparatus of claim 14 , wherein the bridged-tee form filter comprises:
a first resistor coupled between a first node and a second node;
a first inductor and a first capacitor coupled in series between the second node and a third node;
a second capacitor and a second inductor coupled in parallel between the first node and a fourth node; and
a second resistor coupled between the second node and the fourth node.
16. The apparatus of claim 15 , wherein the bridged-tee form filter further comprises:
a third resistor coupled between the third node and a fifth node;
a fourth resistor coupled between the third node and a sixth node;
a third capacitor and a third inductor coupled in parallel between the fifth node and the sixth node.
17. The apparatus of claim 1 , wherein the bi-directional constant impedance filter comprises a bandpass filter.
18. The apparatus of claim 17 , wherein the bandpass filter comprises a pi form filter, a tee form filter, or a bridged-tee form filter.
19. The apparatus of claim 18 , wherein the bridged-tee form filter comprises:
a first resistor coupled between a first node and a second node;
a first inductor and a first capacitor coupled in parallel between the second node and a third node;
a second inductor and a second capacitor coupled in series between the first node and a fourth node; and
a second resistor coupled between the second node and the fourth node.
20. The apparatus of claim 19 , wherein the bridged-tee form filter further comprises:
a third resistor coupled between the third node and a fifth node;
a fourth resistor coupled between the third node and a sixth node; and
a third inductor and a third capacitor coupled in series between the fifth node and the sixth node.
21. The apparatus of claim 1 , wherein the constant impedance is approximately 100 ohms.