DIFFERENT TYPE OF CELLS

DIFFERENT TYPE OF CELLS:

• STDCELLS:
• Nothing But Base cells(Gates,flops).

• TAP CELLS:
• Avoids Latch up Problem(Placing these cells with a particular  distance).
• Cells are physical-only cells that have power and ground pins and dont have signal pins.
• Tap cells are well-tied cells that bias the silicon infrastructure of n-wells or p-wells. 
• They are traditionally used so that Vdd or Gnd are connected to substrate or n-well respectively.
• This is to Help TIE Vdd and Gnd which results in lesser drift and prevention from latchup.
• Required by some technology libraries to limit resistance between Power or Ground connections to well of the substrate.

• TIE CELLS :
• It is used for preventing Damage of cells; Tie High cell(Gate One input is connected to Vdd, another input is connected to signal net);Tie low cells Gate one input is connected to Vss, another input is connected to signal .
• Tie - high and Tie - low cells are used to connect the gate of the transistor to either Power and Ground.
• In lower technology nodes, if the gate is connected to Power or Ground. The transistor might be turned "ON/OFF" due to Power or Ground Bounce.
• These cells are part of the std cell library.
• The cells which require Vdd(Typically constant signals tied to 1) conncet to tie high cells.
• The cells which require Vss/Vdd (Typically constant signals tied to 0) connect to tie low cells. 

• END CAP CELLS:
• To Know the end of the row,and At the edges endcap cells are placed to avoid the cells damages at the  end of the row to avoid wrong laser wavelength for correct manufacturing.
• You can add Endcap cells at both Ends of a cell row.
• Endcap cells surrounding the core area features which serve as second poly to cells
• placed at the edge of row.
• The library cells do not have cell connectivity as they are only connected to Power and Ground rail,
• Thus ensure that gaps do not occure between "WELL" and "IMPLANT LAYER" and to prevent the DRC violations by satisfying "WELL TIE - OFF" requirements for core rows we use End cap cells.
• Usually adding the "Well Extension" for DRC correct designs.
• End caps are a "POLY EXTENSION" to avoid drain source SHORT

• DECAP CELLS:
• Charge Sharing;To avoid the Dynamic IR drop ,charge stores in the cells and release the charge to Nets.
• Decoupling capacitor cells , or Decap cells, are cells that have a capacitor placed.
• Between the Power rail and Ground rail to Over come Dynamic voltage drop.
• Dynamic IR Drop happens at the active edge of the clock at which a High currents is drawn from the Power Grid for a small Duration.
• If the Power is far from a flop the chances are there that flop can go into Metastable State.
• To overcome decaps are added , when current requirements is High this Decaps discharges and provide boost to the power grid.

• FILLER CELLS:
• Filler cells are used to connect the gaps between the cells after placement.
• Filler cells are ussed to establish thecontinuity of the N-Wells and the IMPLANT LAYERS on the standard cells rows, some of the cells also don't have the Bulk Connection (Substrate connection) Because of their small size (thin cells).
• In those cases, the abutment of cells through inserting filler cells can connect those substrates of small cells to the Power/Ground nets.
• i.e. those tin cells can use the Bulk connection of the other cells(this is one of the reason why you get stand alone LVS check failed on some cells)

• ICG CELLS:
• Clock gating cells ,to avoid Dynamic power Dissipation.
• Register banks disabled during some clock cycles.
• During idle modes, the clocks can be gated-offs to save Dynamic power dissipation on flipflops.
• Proper circuit is essential to achive a gated clock state to prevent false glithes on the clock paths

• POWER GATING CELLS:
• In Power gating to avoid static power Dissipation.
• Power Gating Cells:
• Power switches
• Level Shifters
• Retention registers
• Isolation cells
• Power controler

• PAD CELLS:
• To Interface with outside Devices;Input to of Power,Clock,Pins are connected to pad cells and outside  also.

• CORNER CELLS:
• Corner Pads are used for Well Continity.
• To lift the chip.

• MACRO CELLS:
• Memories.
• The memory cells are called Macros.
• To store information using sequntial elements takes up lot of area.
• A single flipflop could take up 15 to 20 transistors to store one bit store the data efficiently and also do not occupy much space on the chip comparatively by using macros.

• SPARE CELLS:
• Used at the ECO.
• Spare cells are standard cells  in a design that are not used by the netlist.
• Placing the spare cells in your design provides a margin for correcting logical error that might be detected later in the design flow, or for adjusting the speed of your design.
• Spare cells are used by the fix ECO command during ECO process.

• PAD FILLER CELLS:
• Used for Well Continity, Placed in between Pads.

• JTAG CELLS:
• These are used to check the IO connectivity.