$${Q_1}$$ :reverse active

$${Q_2}$$; normal active

$${Q_3}$$; :saturation;

$${Q_4}$$ :cut-off

$${Q_1}$$ :reverse active

$${Q_2}$$: saturation

$${Q_3}$$: saturation

$${Q_4}$$ : cut-off

$${Q_1}$$ : normal active

$${Q_2}$$; cut-off

$${Q_3}$$; cut-off

$${Q_4}$$ : saturation

$${Q_1}$$ : :saturation

$${Q_2}$$: :saturation

$${Q_3}$$ :saturation

$${Q_4}$$ : normal active