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U. Glaeser

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FIGURE 21.18 HSPICE waveforms for clock-powered approach when V ϕ is 2.4 V.<br />

FIGURE 21.19 Energy vs. delay for the driver experiment. For comparison purposes, it should be noted that the<br />

delay of a minimum size inverter (nFET width 0.7 µm, pFET width 2.2 µm) was recorded at 150 ps by simulating a<br />

15-stage ring oscillator in HSPICE (supply voltage 3.3 V).<br />

The clock voltage swing, Vϕ, of the clock-powered logic, was varied from 1.1 to 3.3 V. Specifically,<br />

simulations were performed for the following clock voltage swings: 1.1, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7, 3.0,<br />

and 3.3 V. Switching time Ts was varied from nearly 0 to 1 ns (0.001, 0.25, 0.50, and 1.0 ns). For all<br />

simulations the phase width Tw was set to 2.5 ns, whereas the phase high time Th was equal to Tw − 2Ts (see Fig. 21.16(a)). The delay was recorded from the point where the phase started switching until the<br />

output xl reached the 50% point (e.g., 1.65 V in Fig. 21.18). If the delays were evaluated from when the<br />

phase reached its 50% point, the clock-powered approach would be allowed a longer start time than<br />

the conventional case. To eliminate this advantage, the delay was evaluated as described previously (see<br />

Fig. 21.18). VddL was varied identically to Vϕ for the conventional case. The switching time of the inputs<br />

Din and Din<br />

was 1 ps. Delay was measured from the Din 50% point to the xl 50% point (i.e., 1.65 V).<br />

The energy versus delay results (Fig. 21.19) show that the delay of the inverter increases significantly<br />

as VddL is reduced. At 3.3 V, the delay is approximately 0.7 ns, whereas at 1.1 V, the delay is nearly 3.6 ns<br />

(not shown in Fig. 21.19). The conventional driver with the two pull-ups (Fig. 21.17(c)) has a performance<br />

© 2002 by CRC Press LLC<br />

Energy (pJ)<br />

Wave<br />

phD<br />

bootNode<br />

xp<br />

xl<br />

10 0<br />

10 -1<br />

Symbol<br />

Voltages (lin)<br />

*****************************<br />

4.8<br />

4.6<br />

4.4<br />

4.2<br />

4<br />

3.8<br />

3.6<br />

3.4<br />

boot node<br />

3.2<br />

3<br />

2.8<br />

2.6<br />

2.4<br />

2.2<br />

2<br />

1.8<br />

x l<br />

1.6<br />

1.4<br />

1.2<br />

1<br />

800m<br />

600m<br />

400m<br />

200m<br />

0<br />

ϕ D<br />

x ∧ϕ p D<br />

11n 11.5n 12n 12.5n 13n 13.5n 14n<br />

Time (lin) (TIME)<br />

14.5n 15n 15.5n<br />

Delay<br />

0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2<br />

Delay (ns)<br />

Inverter<br />

Modified Inv.<br />

CB (0.001ns)<br />

CB (0.25ns)<br />

CB (0.50ns)<br />

CB (1.00ns)

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