CMOS circuit device design calculation method

First, CMOS circuit device design

To design CMOS circuits, in general, according to user requirements and given circuit indicators, first design each device in the circuit, then draw a published drawing, and finally determine the process parameter. This section mainly introduces CMOS circuit device design and layout design. CMOS circuit device.

Since the inverter is the basis of the circuit, first consider the design of each component of the inverter. CMOS circuit device. In the design of CMOS inverters, the high-level and low-level requirements can be ignored. The main design indicators are the highest operating frequency and noise tolerance. The design indicators and process parameters are given in Table 5-4.

CMOS circuit device design

1, device size calculation

According to the given conditions, we can calculate from the working frequency. To achieve the best speed, you should select , because , therefore:

CMOS电路器件设计

In order to meet the requirements of the highest operating frequency, the rise and fall times are set to be smaller, assuming .

In order to ensure that the circuit works well within the specified range, the "worst case" design should also be adopted. CMOS circuit device. For the operating frequency, low power supply voltage, high threshold voltage, thick oxide layer and large load capacitance are unfavorable factors, so the following data should be taken when calculating:

CMOS circuit device design

(1) Calculation of load pipe

First, write the normalized threshold voltage based on the worst-case data:

CMOS circuit device design

Calculate according to the formula (2-86):

CMOS circuit device design

According to (2-77) type, available:

CMOS circuit device design

Because image. png , the width to length ratio of the load tube can be obtained:

CMOS circuit device design

(2) Input tube calculation

According to (2-82) formula:

CMOS电路器件设计

So, it can be obtained:

CMOS circuit device design

by image. png , the width to length ratio of the input tube is calculated as:

CMOS circuit device design

If If the channel length is 10 μm, the channel width of the load tube is 140 μm, and the channel width of the input tube is 60 μm.

If the calculated unit is a two-input NAND gate circuit, since the load tube is connected in parallel, , so the channel width to length ratio of the two load tubes is the same as the size of the inverter load tube above; CMOS circuit device. The input tubes are connected in series, , so each input tube The aspect ratio should be twice that of the input tube of the inverter above.

2. Noise tolerance calculation

According to the definition of maximum noise capacity: High level maximum voice capacity, low-level maximum noise . Therefore, as long as the conversion level is calculated, the noise capacity is determined. CMOS circuit device. For the worst condition of high-level noise, , the conversion level can be calculated according to formula (2-68):