Question

short notes on three state device​

Answer 1

Explanation:

COMBINATIONAL LOGIC DESIGN

Three State Devices

The electrical design of CMOS and TTL devices whose outputs may be in one of three states—0, 1, or Hi-Z.

Three-State Buffers

The most basic three-state device is a three-state buffer, often called a three-state driver. The logic symbols for four physically different three-state buffers are shown in Figure 1.

Figure 1: Three state buffers (a) noninverting, active-high enable (b) noninverting, active-low enable (c) inverting, active-high enable (d) inverting, active-low enable

The basic symbol is that of a noninverting buffer (a, b) or an inverter (c, d). The extra signal at the top of the symbol is a three-state enable input, which may be active high (a, c) or active low (b, d). When the enable input is asserted, the device behaves like an ordinary buffer or inverter. When the enable input is negated, the device output “floats”; that is, it goes to high impedance (Hi-Z), disconnected state and functionally behaves as if it weren’t even there.