I need to construct a logic bias driver circuit for an a RF SPDT switch.
It negative signal two differentiate logic high and logic low.
The logic requirement is (low= 0V~ -0.5V , high= -3V~ -7V)
The recommended driver circuit is as below.
Can SN74HCS04 driven by a negative supply? Will it produce the state high, low as above?
thanks
Kumar
The SN74HCS04 (like other logic gates) requires that the voltage difference between its VCC and GND pins is at most 5 V, and, most importantly, that the voltages at its input and output pins is between these. The 5.1 V Zener diode indeed ensures that these requirements are met by shifting the input signal down. (Instead of the SN74HCS04, you could also use the two-channel SN74LVC2G14.)
Alternatively, generate the negative signal with a 10 V comparator with an open-drain output, e.g., TL331(B) or TLV1701:
