SL560

Three high performance transistors SL560 of identical geometry are employed. Advanced design and processing techniques enable these devices to combine a low base resistance (Rbb') of 17W (for low noise operation) with a small physical size - giving a transition frequency, fT, in excess of 1GHz.

The input transistor (TR1) SL560 is normally operating in common base, giving a well defined low input impedance. The full voltage gain is produced by this transistor and the output voltage produced at its collector buffered by the two emitter followers (TR2 and TR3). To obtain maximum bandwidth the capacitance at the collector of TR1 must be minimised. Hence, to avoid bonding pad and can capacitances, this point is not brought out of the package. The collector load resistance of TR1 is split, the tapping being accessible via pin 5. If required, an external roll-off  apacitor can be fixed to this point.

The large number of circuit SL560 nodes accessible from the outside of the packages affords great flexibility, enabling the operating current and circuit configuration to be optimised for any application. In particular, the input transistor (TR1) can be operated in common emitter mode by decoupling pin 7 and using 6 as the input. In this configuration, a 2dB noise figure (RS = 200W) can be achieved. This configuration can give a gain of 35dB with a bandwidth of 300MHz (see figs. 10 and 11).

Because the transistors SL560 used in the SL560C exhibit a high value of fT, care must be taken to avoid high frequency instability. Capacitors of small physical size should be used, the leads of which must be short as possible to avoid oscillation brought about by stray inductance. The use of a ground plane is recommended.