• JFET offer better thermal stability as compared to BJTs. Increase in JFET temperature results in decrease in the depletion region width and decrease in the carrier mobility. Decrease in the width of depletion region results in increase in channel width, which in turn increases in ID. This results in positive temperature coefficient for ID.

• Increase in ID with temperature results in increase in VGS (off) with temperature. VGS (off) also has a positive temperature coefficient of the order of 2.2 mV/°C.

• Decrease in carrier mobility gives ID negative temperature coefficient. Since both the mechanisms occur simultaneously, the effect of one mechanism compensates for the other

• Therefore, JFETs offer better temperature stability. A factor of proportionality between changes in ID and corresponding change in VGS isg_m, the Transconductance or Mutual conductance of JFET.

• Hence, combining two effects that cause variation in IDID in opposite directions, the condition for zero drain current drift is

$0.007|I_{D}|$=0.0022gm

$0.007|I_{D}|$=0.0022gm

|ID| / gm=0.314

V|ID|gm=0.314V

Modulus sign in relation is used to cover both types of JFETs, i.e. n- and p-channel. It can be proved that condition for zero current drift in terms of VPVP is |VPVP| - |VGSVGS|= 0.63 V. The proof involves making use of relations

$I_{D}=I_{DSS}(1-V_{GS} / V_{P})^{2}$

$g_{m}=g_{mo}(1-V_{GS} / VP)$

$g_{mo}=-2I_{DSS} / V_{P}$