This circuit works as a bipolar-current source when the voltage drop across source resistor R6 becomes larger than the gate-threshold voltage of depletion-mode MOSFETs Q1 and Q2, thus limiting the current through clamping
Figure 2. This circuit works as a bipolar-current source when the voltage drop across source resistor R6 becomes larger than the gate-threshold voltage of depletion-mode MOSFETs Q1 and Q2, thus limiting the current through clamping