Not sure I can see the reason for the two series diodes. The bottom one is a DC clamp to earth for the gate, but the top one?

Thanks,

Jan

 

Looks like the two diodes center the average bias voltage on the cap right between the supply voltage rails.

The upper one clamps the gate to the upper rail +0.6 V.

 

Sometime to protect from high voltage spikes/surges/static charges, people use such back to back diode from gate to the Gnd and Vcc. If gate voltage goes less than Gnd then lower diode conducts, if gate voltage goes higher than Vcc then upper diode conducts. Thus it saves the gate of the FET.

 

it's kind of pathway for pulse currents to travel - so such "termination" may occasionally (when it does not pose extra capasitive load) enable/speed up the voltage change http://application-notes.digchip.com/009/9-12559.pdf
just noticed something new in HERE
figure_01.gif

 

Thanks for the replies. Very helpful.