With decreasing feature sizes, lowered supply voltages and increasing operating frequencies,
the radiation tolerance of digital circuits is becoming an increasingly important
problem. Many radiation hardening techniques have been presented in the literature for
combinational as well as sequential logic. However, the radiation tolerance of clock generation
circuitry has received scant attention to date. Recently, it has been shown that in
the deep submicron regime, the clock network contributes significantly to the chip level
Soft Error Rate (SER). The on-chip Phase Locked Loop (PLL) is particularly vulnerable to
radiation strikes. In this thesis, we present a radiation hardened PLL design. Each of the
components of this design-the voltage controlled oscillator (VCO), the phase frequency
detector (PFD) and the charge pump/loop filter-are designed in a radiation tolerant manner.
Whenever possible, the circuit elements used in our PLL exploit the fact that if a gate
is implemented using only PMOS (NMOS) transistors then a radiation particle strike can
result only in a logic 0 to 1 (1 to 0) flip. By separating the PMOS and NMOS devices,
and splitting the gate output into two signals, extreme high levels of radiation tolerance
are obtained. Our design uses two VCOs (with cross-coupled inverters) and charge pumps,
so that a strike on any one is compensated by the other. Our PLL is tested for radiation
immunity for critical charge values up to 250fC. Our SPICE-based results demonstrate that
after exhaustively striking all circuit nodes, the worst case jitter of our hardened PLL is just
37.4 percent. In the worst case, our PLL returns to the locked state in 2 cycles of the VCO clock,
after a radiation strike. These numbers are significant improvements over those of the best
previously reported approaches.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-08-8547 |
| Date | 2010 August 1900 |
| Creators | Kumar, Rajesh |
| Contributors | Khatri, Sunil P. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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