Programmable Logic Devices:Dynamic PLA.

By -
Dynamic PLA

If we want to realize a PLA in CMOS, instead of static nMOS circuit that has been discussed in Chapter 33, Section 33.3, in order to save power consumption, then a PLA in CMOS requires a large area because we need pMOS and nMOS subcircuits. Thus, instead of static CMOS, the dynamic CMOS illustrated in Figure 45.5(a) is usually used. During the absence of a clock pulse of the first- and second-phase clocks, φ1 and φ2 (i.e., during φ1 = φ2 = 0 (low voltage, using positive logic)) shown in Figure 45.5(b), pMOSFETs, T1, T2, and T3, become conductive and nMOSFETs, T4, T5, and T6 become non-conductive precharging vertical lines, P1, P2, and P3. When a clock pulse of the first-phase clock, φ1, appears but a clock-pulse of the second-phase clock, φ2, does not appear yet, i.e., when φ1 = 1 (high voltage) and φ2 = 0, pMOSFETs, T1, T2, and T3, become non-conductive and nMOSFETs, T4, T5, and T6, become conductive. Then, depending on the values of x, y, and z, some verticle lines, P1, P2, and P3 are discharged through some of the nMOSFETs in the AND array. (For example, if y = 0 (low voltage), P1 is discharged through nMOSFETs A.) A clock pulse of the second-phase clock, φ2, is still absent (i.e., φ2 = 0), so pMOSFETs, T7, T8, and T9, become conductive and nMOSFETs T10, T11, and T12, become non-conductive, precharging horizontal lines, f1, f2, and f3. When a clock pulse of the first-phase clock, φ1, is still present, and a clock pulse of the second-phase clock, φ2, appears, i.e., when φ1 = φ2 = 1, pMOSFETs, T7, T8, and T9, become non-conductive and nMOSFETs,T10, T11, and T12, become conductive. Then, some of horizontal lines, f1, f2, and f3, are discharged through some of the nMOSFETs in the OR array, depending on which of the vertical lines, P1, P2, and P3, are still charged.

Comments

Post a Comment

Popular posts from this blog

Square wave oscillators and Op-amp square wave oscillator.

By -
Image
Square wave oscillators If Fourier analysis is performed on a square wave it is found that the waveform is composed of many harmonics of the fundamental frequency. This rich harmonic content makes the square wave particularly useful as a quick test of amplifier performance. Examples of possible results are shown. The simplest way to produce a square wave is to make a sine wave oscillator in one of the ways described earlier, then feed the output to some form of squaring circuit such as a Schmitt trigger. This is the method adopted in most commercial sine/square wave generators. There are, however, several circuits for square wave oscillators and a description of the most common follows. Multivibrator Technically the multivibrator is a relaxation oscillator, working on the charging of a capacitor through a resistor. If a negative edge is applied to the circuit in (a), transistor TR 1 turns off the for time taken for the base voltage to return to 0 V. If the voltage step is
Read more

Timing Description Languages:SDF

By -
Image
SDF Standard Delay Format (SDF) is an ASCII format used to convey timing information between EDA tools. SDF was first developed by Cadence in 1990. Open Verilog International (OVI) approved SDF version 2 in 1993 and SDF version 2.1 and 3 in the following years. Improving SDF version 3 features, resulted in IEEE Standard 1497 [1]. Role of SDF in Design Process SDF can be used in different levels of a design process to annotate timing specifications, including timing data and constraints. Timing constraints are used during the forward-annotation process while timing data are applied during the back-annotation process. Forward-annotation process deals with porting timing constraints to synthesis, floorplanner, layout, and routing tools to meet the required constraints. During the design process, timing data can be back-annotated to analysis tools (including simulators, static timing analysis tools, etc.) to provide more accurate timing representations. SDF Structure An SDF f
Read more

Adders:Carry Look-Ahead Adder.

By -
Image
Carry Look-Ahead Adder As previously stated, the carry, c i +1, produced at the i -th position is calculated as c i +1 = x i · y i ∨ c i ·( x i ⊕ y i ). This means that a carry is generated if both x i and y i are 1, or an incoming carry is propagated if one of x i and y i is 1 and the other is 0. Therefore, letting g i denote x i y i , we have c i +1 = g i ∨ c i p i , where p i = x i ⊕ y i . Here, g i is the formula for the carry generation condition at the i -th position, i.e., when g i is 1, a carry is generated at this position. Substituting g i –1 ∨ p i –1 c i –1 for c i , we get A carry look-ahead adder can be realized according to this expression, as illustrated in Figure 41.10 for the case of four bits [21]. According to this expression, c i +1’s are calculated at all positions in parallel. It is hard to realize an n -bit carry look-ahead adder precisely according to this expression, unless n is small, because maximum fan-in and fan-out restriction is violated at higher
Read more