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U. Glaeser

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FIGURE 3.15 Three-level series gating in conventional ECL circuit.<br />

FIGURE 3.16 Three-level series gating in low-voltage ECL (LV-ECL) circuit.<br />

V BE − V S (=0.6 V) in the top level and 0.5 V BE (=0.45 V) in the second and the third levels. The minimum<br />

|V EE| is 2V BE + V CS , the same as that for a single-level ECL gate. By setting V CS = 0.2 V, the minimum |V EE|<br />

of 2 V is achieved. In reality, V CE may be as low as 0.3 V in switching, but never stays in heavy saturation<br />

region.<br />

A schematic of a 4:1 MUX gate and a toggle flip-flop implemented in the LV-ECL circuit is shown in<br />

Figs. 3.17 and 3.18, respectively. Since the logic stage in the LV-ECL remains the same as that in the<br />

conventional ECL, all ECL circuits can be modified as the LV-ECL circuits.<br />

Table 3.1 compares simulated power dissipation, circuit delay, and element count of the 4:1 MUX gate<br />

in LV-ECL with those in conventional ECL. Compared to the conventional ECL, speed and area penalties<br />

are very small in the LV-ECL, because level shifting is not required for the third-level inputs, the critical<br />

path in the conventional ECL. This compensates for the delay increase in the CML level-shifter.<br />

A number of test circuits, such as a 4:1 multiplexer, a 1:4 demultiplexer, and a 16-bit ripple carry<br />

adder, are fabricated in a 1.2 µm, 15 GHz bipolar technology to demonstrate the feasibility of the LV-ECL.<br />

As illustrated in Figs. 3.19 and 3.20, widely used architecture is used in the multiplexer and the demultiplexer.<br />

The test circuits are implemented on an existing ECL gate array to demonstrate that the LV-ECL<br />

circuit improves performance without design optimization of circuit or layout. Power dissipation, including<br />

© 2002 by CRC Press LLC

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