Distributed amplifier with negative feedback
View Patent ↗A distributed amplifier may include an input transmission line for receiving on an input end an input signal, and an output transmission line for outputting on an output end an output signal. A plurality of amplifier stages may be coupled between intermediate positions on the input and output lines. Feedback impedance may negatively feed back a signal on the output end of the output line to a second end of the input line spaced from the first end of the input line.
1. A distributed amplifier comprising:
an input transmission line for receiving on a first end an input signal;
an output transmission line for outputting on a first end an output signal;
an output line termination impedance coupled to a second end of the output transmission line opposite the first end of the output transmission line;
a feedback impedance directly coupling from the first end of the output transmission line to a second end of the input transmission line spaced from the first end of the input transmission line, the feedback impedance arranged to negatively feed back a signal on the output transmission line to the second end of the input transmission line; and
a plurality of amplifier stages each including an active device having a control terminal and two current-carrying terminals, with the control terminal coupled to the input transmission line at an intermediate position between the first and second ends of the input transmission line, and one current-carrying terminal coupled to the output transmission line at an intermediate position between the first and second ends of the output transmission line.
2. The distributed amplifier of claim 1 , wherein there is no input line termination impedance at the second end of the input transmission line.
3. The distributed amplifier of claim 1 , wherein the feedback impedance includes a feedback resistance.
4. The distributed amplifier of claim 3 , wherein the feedback impedance further includes feedback inductance.
5. The distributed amplifier of claim 1 , further comprising output capacitance in the output transmission line adjacent the first end of the output transmission line.
6. The distributed amplifier of claim 5 , wherein the output capacitance is disposed in the output transmission line between the at least one amplifier stage and a position on the output transmission line where the feedback impedance is coupled to the output transmission line.
7. The distributed amplifier of claim 6 , further comprising a shunt capacitor coupling the intermediate position of the output transmission line to a signal ground.
8. The distributed amplifier of claim 1 , wherein the input transmission line has a characteristic impedance, and the feedback resistance has a value that is greater than the characteristic impedance.
9. The distributed amplifier of claim 8 , wherein the feedback resistance has a value that is greater than twice the characteristic impedance.
10. The distributed amplifier of claim 8 , wherein the feedback resistance has a value that is about ten times the characteristic impedance.
11. A method of amplifying a signal comprising:
inputting an input signal on a first end of an input transmission line;
transmitting the input signal along the input transmission line between the first end and a second end opposite the first end;
amplifying the input signal occurring at a plurality of distributed intermediate positions on the input transmission line between the first and second ends of the input transmission line;
applying the signal amplified at each intermediate position on the input transmission line to a corresponding intermediate position on an output transmission line between first and second ends of the output transmission line;
terminating the first end of the output transmission line with a termination impedance; outputting the signal occurring on the second end of the output transmission line; and
negatively feeding back the signal occurring on the second end of the output transmission line directly to the second end of the input transmission line.
12. The method of amplifying a signal of claim 11 , further comprising not terminating the second end of the input transmission line with a termination impedance.
13. The method of amplifying a signal of claim 11 , wherein negatively feeding back the signal includes negatively feeding back the signal through a feedback impedance.
14. The method of amplifying a signal of claim 11 , wherein negatively feeding back the signal includes negatively feeding back the signal through a feedback resistor.
15. The method of amplifying a signal of claim 14 , wherein negatively feeding back the signal includes negatively feeding back the signal through a feedback inductor.
16. The method of amplifying a signal of claim 11 , further comprising conducting the signal in the output transmission line through an output capacitor in the output transmission line adjacent to the first end of the output transmission line.
17. The method of amplifying a signal of claim 15 , wherein conducting the signal in the output transmission line through the output capacitor includes conducting the amplified signal in the output transmission line through the output capacitor.
18. The method of amplifying a signal of claim 11 , wherein negatively feeding back the signal includes negatively feeding back the signal through a feedback resistance having a value that is greater than a characteristic impedance of the input transmission.
19. The method of amplifying a signal of claim 18 , wherein negatively feeding back the signal includes negatively feeding back the signal through a feedback resistance having a value that is greater than twice the characteristic impedance of the input transmission.
20. The method of amplifying a signal of claim 19 , wherein negatively feeding back the signal includes negatively feeding back the signal through a feedback resistance having a value that is about ten times the characteristic impedance of the input transmission.