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.
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.
