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This article introduces the relevant knowledge of "what is ASIC". In the operation of actual cases, many people will encounter such a dilemma. Then let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

ASIC is an application-specific integrated circuit (Application Specific Integrated Circuit), that is, if we design an integrated circuit for a specific application, it is called ASIC. However, memory, microprocessor, etc., are not called ASIC.

The following describes the types of ASIC:

1. Full-Custom ASIC (full customization): for this type of ASIC, every part of the design starts from scratch. The designer did not use the pre-made door and manually completed the layout of the chip.

2. Standard Cell ASIC (based on standard cells): designers use pre-designed logical units, such as AND,NOR, etc. These doors are called standard units. The advantage of Standard Cell ASIC is that designers save time, money, and risk by using a pre-designed and tested library of standard cells.

Each standard cell uses a full-custom design method and can be optimized individually.

When designing a chip, you need to consider the following goals:

1. Speed (Speed)

two。 Area (Area)

3. Power consumption (Power)

4. Time to Market (Time to Market)

To design ASIC, you need to have a good understanding of CMOS process. Next, we will introduce the CMOS process:

1.1 CMOS process

In the current decade, the chips designed are made by CMOS technology. CMOS is a complementary metal oxide semiconductor (Complementary Metal Oxide Semiconductor). It is composed of NMOS and PMOS. To better understand CMOS, we first need to understand MOSFET transistors.

1.2 MOS transistor

MOSFET stands for metal oxide semiconductor field effect transistor (Metal Oxide Semiconductor field effect transistor). MOS transistor is a voltage-controlled device and a basic unit in large-scale integrated circuit design.

The following is a theoretical diagram of MOS transistors.

The CMOS process consists of NMOS and CMOS transistors, which are used to form high-density and complex large-scale integrated circuits for signal processing. CMOS process has the characteristics of low power consumption, high clock frequency and easy to implement. In digital IC, MOSFET transistors can be thought of as simple switches.

The CMOS inverter requires only one PMOS and one NMOS transistor. The input of the NMOS transistor is the ground switch. When the input logic is "1", it turns on, the output load capacitor discharges, and the output driver is logic "0". The input of the PMOS transistor is the power switch. When the input logic is "0", it is turned on, the output load capacitor is charged, and the output driver is logic "1".

The output load capacitance of the logic gate includes: intrinsic capacitance and external capacitance (wiring, fan out).

The charge carriers of PMOS transistors are holes, and the charge carriers of NMOS are electrons. Because the electron mobility is twice that of the "hole", the rising and falling time of the output is different. To make them the same, the W / L of PMOS is about twice that of NMOS transistors. In this way, PMOS and NMOS can have the same "drive strength" (drive strength). In the standard cell library, the transistor length "L" is always constant. The width "W" value must be changed according to the different driving strength of each door.

1.3Power consumption of CMOS integrated circuits

The main sources of power consumption of CMOS integrated circuits are:

1. Dynamic switching power consumption: due to the charge and discharge of the load capacitor of the circuit

-> given frequency f, the power consumption is: load capacitor * Vdd * Vdd * f

two。 Short circuit power consumption

3. Leakage power consumption

1.4 CMOS transmission gate

The PMOS and NMOS transistors are connected in parallel to form a transmission gate. The transmission gate transmits the input value to the output.

Sequential device

In CMOS, the element that stores logical values (by having a feedback loop) is called a sequential device. The simplest example of a sequential device is a back-to-back connection of two inverters. There are two types of basic timing devices. They are:

1. Latch: a latch is formed when two inverters are connected back to back and connected to a transmission gate output with control input. When the control input is logic "1", the transmission gate is turned on and the input'D' is passed to the output. When the control input is logic "0", the transmission gate is closed and the output is maintained.

2. Flip-Flop: the flip-flop consists of two latches connected in series. The first latch is called master latch (Master latch) and the second latch is called slave latch (slave latch). In this case, the input of the transmission gate is called the clock. The inverted clock is sent to the transmission gate input from the latch.

When the clock input is high, the transmission gate of the main latch is turned on, and the two inverters connected by "D" are input. In addition, due to the reverse phase of the clock, the transmission gate from the latch is closed and the output Q maintains the previous value.

When the clock input is low, the trigger is turned on from the transmission gate of the latch and the output Q is updated to the main latch storage value. In this case, the output Q has nothing to do with the change of the main latch input.

Because the data locked by the main latch in the flip-flop occurs at the rising edge of the clock, this type of flip-flop is called the positive edge flip-flop. If the latch occurs on the negative edge of the clock, the trigger is called the negative edge trigger.

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