The commonly available single-chip regulators (LM340, 7805, 7905, LM317, etc.) have internal band-gap references, and can be used as references. Their accuracy and drift specs are often not as good as the references described above, typically + per -5% with a temperature coefficient of + per - 0.1% per °C.
    All the solid-state references generate higher noise than a resistor handling the same current and voltage - often quite a bit more. Sometimes designers try to filter this noise by putting a bypass capacitor across the device. Due to the very low dynamic impedance of these devices, though, a very large capacitor is needed to filter audio noise - on the order of at least several thousand microfarads.

High Voltage References
   There are three main types of high-voltage references: a high-voltage zener diode, a "pseudo-zener" based on a low-voltage reference, and a gas breakdown tube.
   Zener diodes come in voltages as high as 200V, but are more commonly seen up to 75 or 100V. If higher voltages are needed, zeners can be strung in series. The primary problem with high-voltage zeners is that they have a constant positive temperature coefficient of around 0.1% per °C. Experience has shown that they are fairly prone to burning out (usually shorting) when used in tube circuits. This is likely due to the combination of low maximum surge current (45 mA absolute max for the 100V 1N4764) and the presence of high energy stored in capacitors (energy is proportional to V squared). If high voltage zeners are to be used, running them very conservatively is recommended. The 5 watt 1N5333-5388 series is much more rugged than the 1 watt types (1.5A absolute max for the 100V 1N5378).
   Pseudo-zeners are two-terminal circuits that mimic the effect of a high-voltage zener, but use a low-voltage reference. A high-voltage bipolar transistor or MOSFET dissipates the power, and can be made as arbitrarily powerful as desired.

The low-drift qualities of a good low-voltage reference can be lost if voltage drift in the pass device or resistors is not accounted for. If sophisticated circuits are used to maintain accuracy, the complexity would be more worthwhile put into designing the whole regulator around a low-voltage reference. Fig. 1

shows a typical pseudo-zener circuit.
   Gas breakdown tubes use the constant-voltage property of a low-pressure noble gas discharge. They range from simple neon bulbs to large power regulators. Although they are a shunt device like the zener diode, gas tubes have some unique properties that affect their usage. They do not draw any current until a "starting" voltage is reached, at which point the voltage drops to the operating voltage. The starting voltage is from 10% to 50% higher than the operating voltage. The operating voltage of a given tube can be different each time the tube is powered up, depending on the distribution of the discharge within the tube elements. Power regulators, such as the 0A2 and 0C3, have a fairly high range of range of regulation - as much as 2 volts over an operating range of 5 to 30 mA. However, tubes can be selected that have much better regulation. If the current through the tube is kept fairly constant, the accuracy is better. However, spontaneous shifts in voltage are still possible. So-called reference gas tubes have very low current ratings (typically a few mA) but are specially processed to have very good stability with no erratic shifts in voltage. These reference tubes have a negative temperature coefficient of about 0.002