Negative to Positive Supply Logic Level Shifter

This is a simple circuit for negative to positive supply logic level shifter. This circuit used to shift the logic level from minus to ground (such as MOS) to any logic level and from a plus to ground supply (such as TTL). Here is the circuit:

This circuit uses the 2N3970 that provide a fast switching imes and low rds(on). [Source: National Semiconductor Application Note]