# Power amplifier design circuit

#### chooby

Mar 25, 2018
2
Hey guys, I'm just finishing my undergrad in EE, and we haven't done much work with power amplifiers. Can anyone help me out with the question below? I've watched a bunch of youtube videos but I dont seem to be making any progress on this question. My initial thoughts are to use a Class A amplifier as they have similar efficiency to the question below. Guidance of any kind is very appreciated

"Most amplifiers need some sort of bias up sequence. Suppose you have a 2W RF power amplifier that runs at ~25% efficiency. The power amplifier operates at a drain voltage of 6 V, a drain current of 1.3 A and a gate bias somewhere between -2 V and -1 V. The amplifier requires a bias up sequence as follows:

1) With the drain voltage Vg turned off, the bias voltage must be set to -2V
2) The drain voltage is then turned on to +6V
3) The gate voltage is increased until the amplifier draws 1.3A

The bias up sequence can be done with an integrated bias controller such as the HMC980. However, at 6V and 1.3 A, > 1 Watt is dissipated as wasted heat in this bias controller (hint: why?). Because power is a major constraint on a satellite, design a circuit to provide this bias functionality while dissipating half the power as the HMC980. "

#### davenn

Moderator
Sep 5, 2009
14,297
Hey guys, I'm just finishing my undergrad in EE, and we haven't done much work with power amplifiers. Can anyone help me out with the question below? I've watched a bunch of youtube videos but I dont seem to be making any progress on this question. My initial thoughts are to use a Class A amplifier as they have similar efficiency to the question below. Guidance of any kind is very appreciated

"Most amplifiers need some sort of bias up sequence. Suppose you have a 2W RF power amplifier that runs at ~25% efficiency. The power amplifier operates at a drain voltage of 6 V, a drain current of 1.3 A and a gate bias somewhere between -2 V and -1 V. The amplifier requires a bias up sequence as follows:

1) With the drain voltage Vg turned off, the bias voltage must be set to -2V
2) The drain voltage is then turned on to +6V
3) The gate voltage is increased until the amplifier draws 1.3A

do you have a circuit that all this refers to ?
if so, please post, so we can see exactly what is being referred to

#### chooby

Mar 25, 2018
2
do you have a circuit that all this refers to ?
if so, please post, so we can see exactly what is being referred to

Hi davenn, no circuit was given in the question.

#### davenn

Moderator
Sep 5, 2009
14,297
Hi davenn, no circuit was given in the question.

OK
that makes it more difficult responders to be specific in helping you

lets see what happens

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