Method and apparatus for dual notch ripple filtering
An apparatus includes a self-coupled transformer, a first band stop filter and a tank circuit connected in series with the first band stop filter between first and second windings of the self-coupled transformer. An inductor of the tank circuit acts as an out-of-phase third winding of the self-coupled transformer.
1. An apparatus comprising:
a self-coupled transformer;
a band stop filter; and
a tank circuit connected in series with the band stop filter between first and second windings of the self-coupled transformer;
wherein an inductor of the tank circuit acts as an out-of-phase third winding of the self-coupled transformer, and
the band stop filter is defined in part by the inductor.
2. The apparatus of claim 1 wherein the apparatus provides a dual notch ripple cancellation filter across the self-coupled transformer.
3. The apparatus of claim 2 , further comprising:
a load ladder of resistors and capacitors connected in parallel across the out-of-phase third winding and the band stop filter;
wherein the load ladder is tapped for high, low, and center outputs.
4. The apparatus of claim 3 wherein capacitances of the capacitors of the load ladder are less than capacitances of additional capacitors of the band-stop filter and the tank circuit.
5. The apparatus of claim 2 wherein the first and second windings have an inductance smaller than an inductance of the band stop filter.
6. The apparatus of claim 2 wherein the out-of-phase third winding of the self-coupled transformer has an inductance larger than an inductance of the first and second windings.
7. The apparatus of claim 2 wherein the out-of-phase third winding of the self-coupled transformer has an inductance smaller than an inductance of the first and second windings.
8. The apparatus of claim 2 wherein the out-of-phase third winding of the self-coupled transformer has an inductance larger than an inductance of the band stop filter.
9. The apparatus of claim 2 wherein the out-of-phase third winding of the self-coupled transformer has an inductance smaller than an inductance of the band stop filter.
10. The apparatus of claim 2 wherein the first and second windings have an inductance larger than an inductance of the band stop filter.
11. The apparatus of claim 1 further comprising at least one additional band stop filter connected in parallel with the band stop filter.
12. An apparatus comprising:
a self-coupled transformer;
a band stop filter;
a tank circuit connected in series with the band stop filter between first and second windings of the self-coupled transformer; and
wherein an inductor of the tank circuit acts as an out-of-phase third winding of the self-coupled transformer,
the apparatus further comprises a load ladder of resistors and capacitors connected in parallel across the out-of-phase third winding and the band stop filter,
the apparatus provides a dual notch ripple cancellation filter across the self-coupled transformer, and
the load ladder is tapped for high, low, and center outputs.
13. The apparatus of claim 12 , wherein capacitances of the capacitors of the load ladder are less than capacitances of additional capacitors of the band-stop filter and the tank circuit.