Active step attenuator
View Patent ↗An active step attenuator can attenuate the RF signal from a cable modem or other RF source. The active step attenuator converts the RF energy into a DC control signal that controls the attenuation applied to the RF signal. The voltage of the control signal is proportional to the RF energy, so that the active step attenuator attenuates a stronger RF signal more than a weaker RF signal. The active step attenuator may be in the form of a diplex circuit, one branch of which passes signals in one frequency band without attenuation and the other branch of which actively attenuates signals in another frequency band.
1. A filter circuit for adjusting attenuation of a first signal in response to the power of the first signal without use of an external power source other than the first signal itself, the filter circuit comprising:
a first terminal configured to receive the first signal;
a first element in electrical communication with said first terminal and configured to pass a portion of the first signal that is above a first frequency without attenuation and configured to cause attenuation to a portion of the first signal that is below the first frequency;
a second element in electrical communication with said first terminal and said first element and configured to rectify the first signal;
a third element in electrical communication with said second element and configured to cause attenuation to the first signal; and
a second terminal in electrical communication with said first element and said third element and configured to output the first signal;
wherein the magnitude of said attenuation in said third element is a function of the magnitude of the voltage of the first signal at an input to said third element.
2. The filter circuit of claim 1 , wherein said first signal is an RF signal.
3. The filter circuit of claim 1 , further comprising:
a fourth element in electrical communication with said first element and said second element and configured to pass a portion of the first signal that is below a second frequency without attenuation and configured to cause attenuation to a portion of the first signal that is above the second frequency; and
a fifth element in electrical communication with said first element and said third element and configured to pass a portion of the first signal that is below a third frequency without attenuation and configured to cause attenuation to a portion of the first signal that is above the third frequency.
4. The filter circuit of claim 3 , further comprising:
a first blocking capacitor in electrical communication with said first terminal and with said fourth element; and
a second blocking capacitor in electrical communication with said fifth element and with said second terminal.
5. The filter circuit of claim 4 , further comprising:
a first matching inductor in electrical communication with said first terminal and with said fourth element; and
a second matching inductor in electrical communication with said fifth element and with said second terminal.
6. The filter circuit of claim 1 , wherein said third element comprises a reactive network in electrical communication with a diode in electrical communication with a ground.
7. The filter circuit of claim 1 , wherein said third element comprises a resistive network in electrical communication with a diode in electrical communication with a ground.
8. The filter circuit of claim 7 arranged as a diplex circuit, wherein said first element is in a first branch of said diplex circuit and said second element and said third element are in a second branch of said diplex circuit.
9. The filter circuit of claim 7 , wherein said second element is further configured to multiply the voltage of the first signal and to divide the current of the first signal.
10. The filter circuit of claim 9 , wherein said second element is further configured to multiply the voltage of the first signal by a factor of two and to divide the current of the first signal by a factor of two.
11. The filter circuit of claim 9 , wherein said second element comprises two capacitors and two diodes.
12. The filter circuit of claim 7 , wherein said second terminal is further configured to receive a second signal and said first terminal is further configured to output the second signal.
13. The filter circuit of claim 12 , further comprising a fourth element in electrical communication with said third element and with said second terminal and configured to rectify the second signal.
14. The filter circuit of claim 13 arranged as a diplex circuit, wherein said first element is in a first branch of said diplex circuit and said second element and said third element and said fourth element are in a second branch of said diplex circuit.
15. The filter circuit of claim 14 , wherein said second element is further configured to multiply the voltage of the second signal and to divide the current of the second signal.
16. A filter circuit for adjusting attenuation of a first signal in response to the power of the first signal, the filter circuit comprising:
a first terminal configured to receive the first signal;
a first element in electrical communication with said first terminal and configured to pass a portion of the first signal that is below a first frequency without attenuation and configured to cause attenuation to a portion of the first signal that is above the first frequency;
a second element in electrical communication with said first terminal and said first element and configured to rectify the first signal;
a third element in electrical communication with said second element and configured to cause attenuation to the first signal; and
a second terminal in electrical communication with said first element and said third element and configured to output the first signal;
wherein the magnitude of said attenuation in said third element is a function of the magnitude of the voltage of the first signal at an input to said third element.
17. The filter circuit of claim 16 , further comprising:
a fourth element in electrical communication with said first element and said second element and configured to pass a portion of the first signal that is above a second frequency without attenuation and configured to cause attenuation to a portion of the first signal that is below the second frequency; and
a fifth element in electrical communication with said first element and said third element and configured to pass a portion of the first signal that is above a third frequency without attenuation and configured to cause attenuation to a portion of the first signal that is below the third frequency.
18. The filter circuit of claim 17 , wherein said third element comprises a reactive network in electrical communication with a diode in electrical communication with a ground.
19. The filter circuit of claim 18 , further comprising an amplifier in electrical communication with said first terminal for amplifying said first signal.
20. A bidirectional communications system having a forward path to a subscriber and a return path from a subscriber, forward path signals being transmitted along the forward path and return path signals being transmitted along the return path, further comprising:
a diplex filter having a first branch comprising a high-pass filter circuit and a second branch comprising:
a first low-pass filter circuit;
a first rectifier and voltage multiplier circuit in electrical communication with said first low-pass filter circuit;
an attenuator circuit in electrical communication with said first rectifier and voltage multiplier circuit;
a control diode in electrical communication with said attenuator circuit; and
a second low-pass filter circuit in electrical communication with said attenuator circuit.
21. The system of claim 20 , wherein:
said first low-pass filter circuit is connected in series to said first rectifier and voltage multiplier circuit;
said first rectifier and voltage multiplier circuit is connected in series to said attenuator circuit; and
said attenuator circuit is connected in series to said second low-pass filter circuit.
22. The system of claim 20 , wherein said second branch further comprises a second rectifier and voltage multiplier circuit in electrical communication with said attenuator circuit and with said second low-pass filter circuit.
23. The system of claim 22 , wherein:
said attenuator circuit is connected in series to said second rectifier and voltage multiplier circuit; and
said second rectifier and voltage multiplier circuit is connected in series to said second low-pass filter circuit.
24. A method of adjusting attenuation in response to the power of an RF signal without use of an external power source other than the RF signal itself, the method comprising:
receiving an RF signal that includes a first portion in a first frequency band spectrum and a second portion in a second frequency band above said first frequency band;
high-pass filtering said RF signal to cause attenuation to the first portion in the first band and to pass the second portion in the second band without attenuation;
low-pass filtering said RF signal to pass the first portion in the first band without attenuation and to cause attenuation to the second portion in the second band;
rectifying and multiplying the voltage of the first portion;
causing variable attenuation to the first portion;
low-pass filtering said RF signal to pass the first portion in the first band without attenuation and to cause attenuation to the second portion in the second band; and
outputting said first portion and said second portion;
wherein the magnitude of said variable attenuation is a function of the magnitude of the first portion after the step of rectifying and multiplying the voltage of the first portion.
25. The method of claim 24 , wherein said step of causing variable attenuation comprises passing the first portion through a control diode to ground so and wherein the magnitude of said variable attenuation is a function of the magnitude of the current of the first portion passing through the control diode.