Contents
What does wire load models contain?
The wire load model specifies slope and fanout_length for the logic under consideration along with Resistance, capacitance, and area overhead. The fanout_length attribute specifies the value of the wire length that is associated with the number of fanouts.
What is a wire load?
The load wire connects your light switch to your light fixture. When the switch is “closed”, electricity flows from the light switch to your light fixture, turning on the light. It is usually attached to a brass terminal on the previous switch. It is sometimes black or red. Also known as a hot, live or switch leg wire.
What is meant by zero wire load model?
Re: zero wire load model Wireload model is something which calculates the net delay based on the fanout of a particular gate. Basically its a statistical based model which gives the prelayout estimation.
What is wireload model?
A wireload model is what the synthesis tool uses to estimate wire characteristics (e.g. interconnect delay) in the absence of physical layout data. For a wire with a given fanout, the wireload model specifies the capacitance, resistance, and area of the wire.
What is NLDM in VLSI?
Non-linear Delay Model (NLDM): Nowadays the non-linear delay model (NLDM) or the composite current source timing model (CCS) based look-up table (LUT) is widely used for static timing analysis (STA). The accuracy of timing analysis depends on the accuracy of the delay model used in the cell characterization.
What is non-linear delay model?
Non Linear Delay Model (NLDM) based LUTs are quite common in industries[1]. LDM divides delay curve w.r.t input rise time(trin) into two different region one is linear and other is non-linear. This boundary point between linear and non- linear region was called break point (trb).
Which wire is load?
The easiest way of identifying the line/hot and load wires is to check the colors of the insulation. White and grey wires are neutral; green with yellow stripes, green and copper are ground wires, black can be line/upstream wire, red or black are load/downstream. The white or black are travelers.
What color is the load wire?
The color for the Line wire is usually black and the Load wire is usually red, black, or blue (less common).
Why CCS is more accurate than NLDM?
Driver model requires more granularity in driver model. CCS timing model eliminate need for this synthesis and hence is able to achieve higher accuracy than NLDM. Other significant shortcoming of NLDM is in the receiver model. NLDM receiver model fails capture miller effect.
What is the difference between NLDM and CCS?
CCS: current composite models. The basic difference between CCS and NLDM is : NLDM uses a voltage source for driver modeling (thevenin’s theorem), where as a CCS uses a current source for driver modeling (norton’s theorem). 130nm library (NLDM – say 5% variation with SPICE simulation) characterisation.
What is RC delay in VLSI?
The RC delay model is a metric used in VLSI design to calculate the signal delay between the input voltage and output voltage of the input signal. The input signal is a step function. In this case the transistor can be considered as a switch in series with a resistor. pMOS transistor has a bigger resistance – 2 R .
How is wire load model used in design?
The wire load model depends upon the area of the block, and designs with different areas may choose different wire load models. The wire load model also maps the estimated length of the net into the resistance, capacitance, and the corresponding area overhead due to routing.
Is the wire load model ( WLM ) an obsolete technology?
WLM is an estimation of delay, based on area and fanout. It is obsolete technology and after physical synthesis there’s no use of it. Prior to Routing stage, net parasitics and delays cannot be accurately determined. So, to predict delay we need to know the parasitics associated with interconnect/net:
How to calculate the length of a wire load?
Length = Length of Last fanout number given in the table + (The fanout number we want – Last fanout number in WLM) * Slope Capacitance = New calculated Length * Capacitance coefficient given in the table Area overhead due to interconnect = New calculated Length * Area coefficient given in the table
How are wire load models defined in Synopsys?
The average wire length within a block increases as the block size is increased. Generally, a number of wire-load models are present in the Synopsys technology library, each representing a particular size block of the logic. These models define the capacitance, resistance, and area factor of the net.