IH401A

The IH401A is made up of 4 monolithically constructed combinations of varacitor type diode and a N-Channel JFET. The JFET itself is very similar to the popular 2N4391, and the driver diode is specially designed, such that its capacitance is a strong function of the voltage across it. The driver diode is electrically in series with the gate of the N-Channel FET and simulates a back-to-back diode structure. This structure is needed to prevent forward biasing the source-to-gate or drain-to-gate junctions of the JFET when used in switching applications.

Previous applications of JFETs required the addition of diodes, in series with the gate, and then perhaps a gate-tosource referral resistor or a capacitor in parallel with the diode; therefore, at least 3 components were required to perform the switch function. The IH401A does this same job in one component (with a great deal better performance characteristics).

Like a standard JFET, the practically perform a solid state switch function translator should be added to drive the diode. This translator takes the TTL levels and converts them to voltages required to drive the diode/FET system (typically a 0V to -15V translation and a 3V to +15V shift). With ±15V power supplies, the IH401A will typically switch 22VP-P at any frequency from DC to 20MHz, with less than 50W rDS(ON).