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U. Glaeser

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FIGURE 11.11 (Continued)<br />

mode when φ is LOW and φ is HIGH. In the block diagram, an eight-valued weighted sum of input<br />

currents, I in, enters the QFA’s diode connected NMOS input transistor MN A generating a gate-to-source<br />

voltage V GSA. When in the FOLLOW mode φ is high, turning on NMOS pass transistor MN B, coupling<br />

V GSA to the input of the QFA block as input voltage V 1. In the FOLLOW mode, the input is converted<br />

by the combinational QFA circuit to the quaternary SUM and CARRY output currents. A quantized<br />

regenerated feedback current, I F, is also created by the QFA block to logically replicate the input current.<br />

Simultaneously, the feedback current, IF, generates VGSC in the diode-connected NMOS transistor MNC. φ is LOW disconnecting VGSC from the V1 QFA input node. In the HOLD mode, with φ LOW and φ<br />

HIGH,<br />

transistor MNB, is off, disconnecting the effect of the input current from the input of the QFA. Transistor<br />

MNC is on, connecting the VGSC created by the regenerated feedback current, IF, to the V1 QFA input.<br />

Thus, in the HOLD mode IF regenerates itself with positive feedback through the nonlinear quantizer in<br />

the QFA block. The QFA block in Fig. 11.12 may be realized with a slight modification of the first QFA<br />

presented in this paper. The QFA section of the latched QFA is described next.<br />

© 2002 by CRC Press LLC

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