DG419 Precision CMOS Analog Switches

* oPrecision test equipment

* oPrecision instrumentation

* oBattery powered systems

* oSample-and-hold circuits

* oMilitary radios

* oGuidance and control systems

* oHard disk drives

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* oSwitched Signal Powers Analog Switch The analog switch in Fig. 10 derives power from its input signal, provided the input signal amplitude exceeds 4 V and its frequency exceeds 1 kHz. This circuit is useful when signals have to be routed to either of two remote loads. Only three conductors are required: one for the signal to be switched, one for the control signal and a common return.A positive input pulse turns on the clamping diode D1 and charges C1. The charge stored on C1 is used to power the chip; operation is satisfactory because the switch requires less than 1 µA of stand-by supply current. Loading of the signal source is imperceptible. The DG419’s on-resistance is a low 100 Ω for a 5 V input signal.

* oMicropower UPS Transfer Switch When VCC drops to 3.3 V, the DG417 changes states, closing SW1 and connecting the backup cell, as shown in Fig. 10. D1 prevents current from leaking back towards the rest of the circuit. Current consumption by the CMOS analog switch is around 100 pA; this ensures that most of the power available is applied to the memory, where it is really needed. In the stand-by mode, hundreds of A are sufficient to retain memory data. When the 5 V supply comes back up, the resistor divider senses the presence of at least 3.5 V, and causes a new change of state in the analog switch, restoring normal operation.

* oProgrammable Gain Amplifier The DG419, as shown in Fig. 11, allows accurate gain selection in a small package. Switching into virtual ground reduces distortion caused by RDS(on) variation as a function of analog signal amplitude.

* oGaAs FET Driver The DG419, as shown in Fig.12 may be used as a GaAs FET driver. It translates a TTL control signal into -8 V, 0 V level ou