Level Shifting Buffer
This circuit is a unity gain level shifting buffer. The output bias voltage is shifted upward toward V+ by use of a Zener diode. A PNP resistor also adds an offset of Vbe which is typically about 0.7V. The gain is about 1 and it has a very high frequency response. The total offset is equal to the Zener voltage Vz plus Vbe.
There are times when you want to shift the bias of an AC signal without using caps, especially at low frequencies. Linking capacitors in the path are high pass signals, and so low frequency signals are attenuated. Since this circuit has no caps in the signal path it has good low frequency characteristics.
Level Shifting Buffer Circuit