Amplifier circuit and method
An amplifier arrangement comprises N amplifier stages ( 10 1 to 10 N ). The amplifier arrangement comprises a main cascade of quarter wavelength transmission lines coupled between an output of a main amplifier ( 10 2 ) of the N amplifier stages ( 10 1 to 10 N ) and an output node ( 15 ) of the amplifier arrangement, wherein the main cascade comprises N−1 quarter wavelength transmission lines ( 11 1 to 11 N-1 ). An output of one peaking amplifier ( 10 N ) of the N amplifier stages is coupled to the output node ( 15 ), and remaining peaking amplifiers ( 10 1 , 10 3 to 10 N-1 ) of the N amplifier stages coupled to respective junctions ( 12 1 to 12 N-2 ) in the main cascade of quarter wavelength transmission lines ( 11 1 to 11 N-1 ). The amplifier arrangement is further configured such that at least one of the quarter wavelength transmission lines in the main cascade is extended by a half wavelength transmission line ( 13 ) or multiples of half wavelength transmission lines, and/or at least one of the peaking amplifiers ( 10 - 1 , 10 3 to 10 N ) is coupled to its respective junction or output node ( 15 ) via a connecting half wavelength transmission line ( 13 ) or multiples of half wavelength transmission lines.
1. An amplifier arrangement, comprising:
N amplifier stages coupled to an output impedance network, the output impedance network comprising a cascade of quarter wavelength transmission lines;
a main amplifier and a plurality of peaking amplifiers configured to operate in a Doherty mode of operation;
wherein the amplifier arrangement is configured such that at least two peaking amplifiers are collectively driven by time-delayed versions of the same signal; and
at least one of the following is true:
at least one of the quarter wavelength transmission lines of the cascade is extended by a half wavelength transmission line or multiples of half wavelength transmission lines;
at least one of the peaking amplifiers is coupled to a respective junction or output node of the cascade via a connecting half wavelength transmission line or multiples of half wavelength transmission lines;
wherein the output impedance network comprises a cascade of quarter wavelength transmission lines coupled between an output of the main amplifier of the N amplifier stages and an output node of the amplifier arrangement;
wherein the cascade comprises N−1 quarter wavelength transmission lines; and
wherein an output of one peaking amplifier of the N amplifier stages is coupled to the output node, and remaining peaking amplifiers of the N amplifier stages coupled to respective junctions in the main cascade of quarter wavelength transmission lines.
2. The amplifier arrangement of claim 1 :
wherein the amplifiers are substantially equally sized; or
wherein at least one amplifier is sized differently to the remaining amplifiers.
3. The amplifier arrangement of claim 1 :
wherein an impedance of each section of the cascade of quarter wavelength transmission lines is substantially equal; or
wherein at least one section of the cascade of quarter wavelength transmission lines comprises an impedance which is different to the remaining sections of the cascade.
4. The amplifier arrangement of claim 1 , wherein each of the peaking amplifiers is coupled to a respective junction or output node of the cascade via a connecting half wavelength transmission line or multiples of half wavelength transmission lines.
5. The amplifier arrangement of claim 1 , wherein a half wavelength transmission line comprises:
a single half wavelength transmission line; or
a sectioned quarter wavelength transmission line cascade comprising first and second stages, each of the first and second stages coupled to receive first and second amplifiers.
6. The amplifier arrangement of claim 5 , wherein at least one of the first and second amplifiers is coupled to a respective junction of the sectioned quarter wavelength transmission line cascade via a half wavelength transmission line or multiples of half wavelength transmission lines.
7. The amplifier arrangement of claim 1 :
wherein the amplifier arrangement comprises four amplifier stages; and
wherein a second section of the cascade of quarter wavelength transmission lines is extended by a half wavelength transmission line or multiples of half wavelength transmission lines.
8. The amplifier arrangement of claim 1 :
wherein the amplifier arrangement comprises four amplifier stages; and
wherein a first peaking amplifier is coupled to its respective junction of the cascade of quarter wavelength transmission lines via a half wavelength transmission line or multiples of half wavelength transmission lines.
9. The amplifier arrangement of claim 1 , wherein:
the amplifier comprises four amplifier stages;
a first peaking amplifier is coupled to its respective junction of the cascade of quarter wavelength transmission lines via a half wavelength transmission line or multiples of half wavelength transmission lines;
a second peaking amplifier is coupled to its respective junction of the cascade of quarter wavelength transmission lines via a half wavelength transmission line or multiples of half wavelength transmission lines; and
a third peaking amplifier is coupled to the output node via a half wavelength transmission line or multiples of half wavelength transmission lines.
10. The amplifier arrangement of claim 9 , wherein a second section of the cascade of quarter wavelength transmission lines is extended by a half wavelength transmission line or multiples of half wavelength transmission lines.
11. The amplifier arrangement of claim 1 , wherein a characteristic impedance of each successive stage in the cascade of quarter wavelength transmission lines is reduced towards the output node in relation to the parallel combination of preceding connecting transmission lines, whereby an outgoing transmission line has an admittance that is the sum of all incoming admittances.
12. The amplifier arrangement of claim 1 , wherein a characteristic impedance of each of the half wavelength transmission lines is substantially equal.
13. The amplifier arrangement of claim 1 , wherein:
the amplifier comprises six amplifier stages;
the cascade of quarter wavelength transmission lines comprises five stages;
the main amplifier and first and second peaking amplifiers are substantially double the size of the remaining peaking amplifiers; and
a fifth peaking amplifier is coupled to the output node via a half wavelength transmission line or multiples of half wavelength transmission lines.
14. The amplifier arrangement of claim 1 , wherein the main amplifier and first and second peaking amplifiers are substantially double the size of any remaining peaking amplifiers.
15. The amplifier arrangement of claim 14 , wherein:
the amplifier comprises six amplifier stages;
the main cascade of quarter wavelength transmission lines comprises five stages;
a third peaking amplifier is coupled to its respective junction of the cascade of quarter wavelength transmission lines via a half wavelength transmission line or multiples of half wavelength transmission lines;
a fourth peaking amplifier is coupled to its respective junction of the cascade of quarter wavelength transmission lines via a half wavelength transmission line or multiples of half wavelength transmission lines;
a fifth peaking amplifier is coupled to the output node via a half wavelength transmission line or multiples of half wavelength transmission lines; and
the main amplifier and first and second peaking amplifiers are substantially double the size of the third, fourth and fifth peaking amplifiers.
16. The amplifier arrangement of claim 1 , wherein:
each peaking amplifier is coupled via a half wavelength transmission line to its respective junction in the cascade of quarter wavelength transmission lines or output node; and
the sizes of each of the amplifiers and their corresponding half wavelength line impedances are optimized in relation to a reactive loading effect of the half wavelength transmission lines.
17. The amplifier arrangement of claim 1 , wherein:
the amplifier arrangement is configured to operate at center frequency, or
the amplifier is configured to operate away from center frequency.
18. A method of improving the efficiency of an amplifier arrangement comprising N amplifier stages coupled to an output impedance network, the impedance network comprising a cascade of quarter wavelength transmission lines, wherein the amplifier arrangement comprises a main amplifier and a plurality of peaking amplifiers configured to operate in a Doherty mode of operation, the method comprising:
collectively driving at least two peaking amplifiers by time-delayed versions of the same signal;
at least one of:
extending at least one of the quarter wavelength transmission lines in the cascade by a half wavelength transmission line or multiples of half wavelength transmission lines;
coupling at least one of the peaking amplifiers to its respective junction or an output node via a connecting half wavelength transmission line or multiples of half wavelength transmission lines;
wherein the output impedance network comprises a cascade of quarter wavelength transmission lines coupled between an output of the main amplifier of the N amplifier stages and an output node of the amplifier arrangement;
wherein the cascade comprises N−1 quarter wavelength transmission lines; and
wherein an output of one peaking amplifier of the N amplifier stages is coupled to the output node, and remaining peaking amplifiers of the N amplifier stages coupled to respective junctions in the main cascade of quarter wavelength transmission lines.
19. The method of claim 18 :
wherein each peaking amplifier is coupled via a half wavelength transmission line;
further comprising selecting the sizes of each of the amplifiers and/or their corresponding half wavelength line impedances in relation to a reactive loading effect of the half wavelength transmission lines.