Young_Electronic_00
Newbie level 5
Hello everyone,
I want to consult with you my doubts which appeared during design of Doherty amplifier. I'm designing simple configuration consisting of AB and C amplifiers. Schematic of single amplifier which I used for a carrier and an auxiliary amplifiers looks as follows:
So, for such a circuit, I calculated IV curve to choose biasing (presented below). The pinch-off voltage of the transistor is -0.65 V.
I don't have bigger problem with AB class (Vds = 3.75 V, and Ids = 26 mA what corresponds to Ugs = -0.54 V), however I'm totally confused with C class. I looked through several publications, books, and I've noticed different information how to choose biasing point. On this moment, I'm testing two of them. In first one I choose Vds = 5V, and Vgs = -0.95 V what is signifcantly under the pinch-off voltage (this corresponds to point C on the graph), and the second one: Vds = 2.5 V, and Vgs = -0.7 V (this is almost B class but for different load-line). So I'm confused, because after design of single amplifiers, and use them in Doherty configuration I should see Doherty region, right ? Something like this should be observed:
I see improvment of linearity (comparing to B or AB classes) however, I don't observed such a region...
So, how the biasing of a class C amplifier should be done ? How should the operating point for the HEMT transistor be selected?
Regards,
E
I want to consult with you my doubts which appeared during design of Doherty amplifier. I'm designing simple configuration consisting of AB and C amplifiers. Schematic of single amplifier which I used for a carrier and an auxiliary amplifiers looks as follows:
So, for such a circuit, I calculated IV curve to choose biasing (presented below). The pinch-off voltage of the transistor is -0.65 V.
I don't have bigger problem with AB class (Vds = 3.75 V, and Ids = 26 mA what corresponds to Ugs = -0.54 V), however I'm totally confused with C class. I looked through several publications, books, and I've noticed different information how to choose biasing point. On this moment, I'm testing two of them. In first one I choose Vds = 5V, and Vgs = -0.95 V what is signifcantly under the pinch-off voltage (this corresponds to point C on the graph), and the second one: Vds = 2.5 V, and Vgs = -0.7 V (this is almost B class but for different load-line). So I'm confused, because after design of single amplifiers, and use them in Doherty configuration I should see Doherty region, right ? Something like this should be observed:
I see improvment of linearity (comparing to B or AB classes) however, I don't observed such a region...
So, how the biasing of a class C amplifier should be done ? How should the operating point for the HEMT transistor be selected?
Regards,
E