IR drop, EM, noise and antenna

1. IR Drop

IR Drop It refers to a phenomenon of voltage drop and rise on the power supply and ground network in an integrated circuit . Due to the continuous evolution of Technology , The width of metal interconnects is getting narrower , The resistance value is increasing , The supply voltage is getting smaller and smaller ,IR Drop The effect of is becoming more and more obvious . therefore , Now the chips are finally IR Drop As a chip signoff A necessary step of . The tool uses Redhawk.

1.1 IR Drop The classification of

IR Drop There are two main types . One is Static IR Drop, The other is Dynamic IR Drop.

static state IR Drop The main reason is the partial voltage of the metal connection of the power network , Caused by the resistance partial voltage of the metal wiring itself . The static voltage is mainly related to the structure and detailed wiring of the power network .

static state IR Drop Mainly consider the resistance effect , Analyze the effect of resistance .

dynamic IR Drop The cause is the voltage drop caused by current fluctuation when the power supply is switched , Occurs on the trigger edge of the clock , The clock edge jump causes a large number of transistor switches , Bring about the jump of combinational logic circuit , Make the chip generate a large current in a short time .

The more transistors the switch has , The easier it is to trigger dynamics IR Drop The phenomenon .

1. 2 IR drop Influence

• Performance degradation , When the voltage drops ,gate The switching speed of becomes slow , Performance degradation . So for high-performance design ,IR Drop It needs to be controlled within a very small range .
• Lead to setup and hold Violation , If power network Not good enough ,IR drop Especially large in a local area （ Especially dynamic IR Drop）, Which leads to STA Stage signoff Of timing Not consistent with the actual situation .

setup The violation of can raise the frequency by raising the voltage , But the power consumption goes up , And if dynamic IR drop Not enough robust, By raising the voltage ,setup There is also limited room for improvement .
Once it appears hold Violation , Then the chip will not work properly . Therefore, in advanced technology ,IR Drop The impact is particularly great , It needs to attract your great attention .

1.3 improve IR Drop Methods

• Improve PG density , increase power switch cell Number , enhance PG Strength of
• Insert enough decap cell（ Including decoupling capacitor ）
• Stagger the flipped registers row put

2. EM

EM( Electromigration )： Metal as interconnection , When the current is too high , Electrons collide with atoms inside the metal , Cause metal to heat , The resistance increases , When a large number of collisions occur in a short time , Metal atoms will flow in the direction of electrons , This phenomenon is called Electromigration .
Interconnection ：IC The internal use of metal film to conduct the working current is called interconnection .

2.1 EM influence

• Electromigration will make IC There is a short circuit or open circuit in the interconnection line , cause IC invalid .
• Increase the grid resistance of the power supply , Affect circuit timing

2.2 improve EM Method

• You need to double the width of the line
• increase via The number of

3. Noise Violation

noise Also known as crosstalk( crosstalk ), Mainly refers to Process metal layer line narrowed , After the spacing becomes smaller , As a result, the coupling capacitance between lines increases , The grounding capacitance becomes smaller . and Noise The size of is directly proportional to the coupling capacitance , It is inversely proportional to the grounding capacitance . So lead to Noise The impact of .

noise The impact of is mainly divided into two categories ： Signal delay and burr
Based on the analysis of noise when , Will produce noise The network of signal sources is called infringement net, Networks that are subject to crosstalk are called victims net. When the signal of network infringement is 0 and 1 When the level changes between , The affected network will generate corresponding crosstalk noise .

3.1 Repair noise violation Methods

• Enhance victimization net The driving power of ,upsize driver
• To the victim net Add buffer, insert buffer It's back-end repair violation Universal means . It also deals with noise It is a very effective repair technology . By inserting buffer Breaking the long line can effectively reduce the victims net Coupling capacitance on , To reduce noise Influence .
• Reduce the length of parallel routes , change net Routing
• Put two net Increase the spacing between or shield wire shield To protect victims net
• Reduce the driving power of infringing network

4. antenna violation

antenna violation( Antenna effect )： In the process of chip production , Exposed metal wires and other conductors , Like antennas Collect charge Cause the potential to rise . When there is enough charge, it will discharge , Probably breakdown MOS The grid of the tube , Disable the circuit , Namely Antenna effect .
With the development of Technology , The size of the grid is getting smaller and smaller , There are more and more layers of metal , The more likely the antenna effect is .

4.1 Elimination method of antenna effect

The method to solve the antenna effect can be divided into jumper sending ( Upper jumper and lower jumper )、 Plug in the diode 、 insert buffer.
1. Upward jumper method

2. Downward jumper method

This method solves the antenna effect by changing the level of metal wiring , But at the same time, through holes are added , Because the resistance of the through hole will directly affect the timing and crosstalk of the chip , Therefore, strictly control the change of wiring level and the number of through holes .
These two methods , Among them, the upward jumper method is the most commonly used , Only when the antenna effect appears on the top metal layer , Just consider jumping down . But the effect is not obvious , You can directly use another method below , insert buffer Cut off the long line .

3. Insert the reverse diode
Insert a grounded diode into the metal connection line , When the charge accumulates to a certain extent , It will form a path to the ground , But inserting a diode will increase the chip area , It is not suitable to adopt .

4. insert buffer
Insert buffer Cut off the long line , Solve the antenna effect .

5.sizeup cell
Increase the area of the grid to reduce the antenna effect

6. add to dummy load load
The essence is to increase gate To alleviate the antenna effect . Generally used for smaller violation The situation of .