15.01.2013 Views

U. Glaeser

U. Glaeser

U. Glaeser

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

n +<br />

SiO 2<br />

FIGURE 2.80 No reverse body effects.<br />

FIGURE 2.81 Cross talk suppression.<br />

A problem in such development is cross talk, which is the effect that the switching noise generated by<br />

the digital circuit block has on the high precision analog circuit via the substrate. With SOI structures,<br />

as shown in Fig. 2.81, it is possible to reduce the effect of this cross talk by using a high-resistance SOI<br />

substrate (having a resistivity of 1000 Ω cm or more, for example) to create a high impedance in the noise<br />

propagation path [5]. Furthermore, even with an ordinary SOI substrate, by surrounding the analog circuit<br />

with N+ active SOI layer and applying a positive bias to it to form a depletion layer below the buried<br />

oxide layer, it is possible to suppress the propagation of the noise [6]. Although guard ring structures and<br />

© 2002 by CRC Press LLC<br />

Si Substrate<br />

V BS > 0<br />

High-resistivity<br />

SIMOX-sub<br />

B<br />

S<br />

Ultrathin-Film SOI Conventional Bulk<br />

n +<br />

lower V TH<br />

Digital Analog<br />

1 mV<br />

> 1000 Ωcm SIMOX-sub.<br />

n +<br />

GND<br />

V DD<br />

GND<br />

OUT<br />

n<br />

p<br />

+ n +<br />

P-Well<br />

Digital Analog<br />

1 mV<br />

P-type<br />

SIMOX-sub.<br />

Digital<br />

n +<br />

V BS ≤ 0<br />

1 mV<br />

P-type<br />

SIMOX-sub.<br />

Guard<br />

Ring<br />

N +<br />

Depleted layer<br />

GND<br />

Analog

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!