Bias circuitry for depletion mode amplifiers

A circuit, comprising:

• (A) an amplifier section comprising an output transistor, the output transistor having:
• a source electrode;
• a drain electrode;
• and a gate electrode;
• (B) a bias circuit, comprising:
• (a) a current source;
• (b) biasing circuitry connected to a voltage source and connected between the current source and the gate electrode of the output transistor;
• (C) a transistor switch having a pair of electrodes serially connected between the voltage source and the bias circuit for, while the biasing circuitry is connected to the voltage source either:
• (i) electrically coupling the voltage source to the current source;
• or (ii) electrically decoupling the voltage source from the current source, selectively in accordance with a control signal fed to a control electrode of the transistor switch;
• and
• (D) wherein the bias circuit changes an amount of current passing through the drain electrode and the source electrode in accordance with whether:
• (i) the voltage source is electrically coupled to the current source or, (ii) the voltage source is electrically decoupled from the current source and;
• (E) wherein:
• the biasing circuitry comprises:
• a biasing circuit transistor serially connected between the current source and a reference potential;
• a voltage level shifting circuit, serially connected between the voltage source and a potential more negative than the reference potential independent of the control signal fed to the transistor switch, for establishing a predetermined voltage at a gate electrode of the biasing circuit transistor;
• and
• wherein the gate electrode of the biasing circuit transistor is coupled to the gate of the output transistor.