Low power digital CMOS compatible bandgap reference

DETAILED DESCRIPTION The following description of the invention will often refer to exact numerical values used in analyzing the invention.
This is done solely to demonstrate the advantages of the invention over the prior art.
The invention need not be limited to such exact values, as will be apparent to one reasonably skilled in the art.
In addition to the conventional area ratioed diodes (8:1), the invented bandgap reference circuit in one embodiment enjoys common centroid layout techniques that are further used to improve the manufacturing sensitivities.
The embodiment uses 1 to 1 ratioed gain resistors and a common centroid 6:1 current mirror further improving manufacturing sensitivities.
The proposed implementation also exhibits very fast turn on and recovery characteristics for low power and power down applications.
All of the above techniques are fully compatible with standard digital CMOS fabrication processes.
FIG.
3 illustrates a first embodiment of the invention.
A reference circuit 300 is shown having an output node 301 presenting an output voltage V.
sub.
bg that remains substantially invariant with respect to temperature variations and limited variations in supply voltage at the supply node 305.
To achieve V.
sub.
bg, the circuit 300 incorporates current mirror subcircuit 311 controlled by amplifier 317.
Amplifier 317 forces its two complementary input nodes 307 and 309 to approximately the same potential in the steady state.
The amplifier does so by driving the current mirror subcircuit which in this embodiment is represented by the three p-channel MOS transistor elements 313, 315 and 325 whose gates are coupled to output 303 of the amplifier.
The two complementary input nodes 307 and 309 have diode-like elements D1 and D2 connecting them respectively to a common second supply node 321 as shown, with resistor R.
sub.
1 in series with D2.
Diodes D1 and D2 have geometries that define an area ratio typically greater than 1.
In this embodiment, the D2:D1 area ratio is preferably 8:1 for practical reasons (common centroid), where D2 is actually eight separate smaller devices, each smaller device having the same geometry as D1 which is placed in the center of a 3