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The working principle of E/EMOS inverter and the influence of inverter performance

Source: Time:2020-10-28

The working principle of E/EMOS inverter and the influence of inverter performance

E/EMOS inverter working principle

1. Working principle

In the E/EMOS inverter circuit, the load tube usually has two bias states. One is the gate-drain common connection power supply VDD, called saturated MOS load; the other is the gate single connection power supply, Called the unsaturated MOS load. The connection methods of these two load MOS transistors are shown in Figure 2-5. The working principles of these two inverters are discussed below.

E/EMOS倒相器工作

1. Saturated MOS load inverter

(1) I-V characteristics of the load tube

In Figure 2-5(a), TL is a MOS load device with a common gate-drain connection. It is different from the pure resistive load mentioned above. A variable resistor that changes with the source voltage. due to VDD= E/EMOS倒相器工作，VDS, So it meets . Therefore, it always works in the saturation zone. In addition, we can see that the source voltage Vs of the load tube changes,Therefore, the gate bias voltage VGS will also change, and the channel resistance will also change. This is the gate bias voltage VGS is modulated by the source voltage VS.Figure 2-6(a) shows E/EMOS inverter Schematic diagram of the cross-section of the channel modulation of the work .

When the source voltage of the load MOS transistor increases, it will cause a gate The source voltage VGS becomes smaller, which makes the channel thinner and the channel resistance increases, so the current Ios also gradually decreases. Figure 2-6(b) is the I-V characteristic curve of a common-gate-drain MOS load. It can be seen that when Vs=0,VDDThe largest, so Im is also the largest. When Vs increases, VGS becomes smaller, and Ios gradually decreases; when a increases to equal VDD-VT, then VGS-VT, the load tube is in the micro-conduction state, so IDS≈0。

From the IV characteristic curve of the total leakage negative I tube, it can be seen that its IV characteristic is a curve, indicating that the load tube is a variable resistor. When Vs changes from 0V to VDD-VT, the resistance value becomes larger and larger.

(2) Inverter operating point

The principle of phase inversion of the saturated load MOS inverter is the same as the principle of the above-mentioned resistive load inverter. When inputting "1" level (), input MOS tube guide Pass. In fact, the load tube is also on at this time, but the on-resistance of the sub-input tube is designed to be much smaller than the on-resistance of the load tube. The power supply voltage is V DD mostly land on the load tube TL, so the output voltage is "0" level.

When the input is "0" level, the input MOS tube is completely cut off , Its cut-off resistance is very large, and most of the power supply voltage falls on, So the output is "1" level. At this time, the on the load tube is in a micro-conduction state. The two output characteristic curves of the input tube cut-off and on-state are shown in Fig. 2-8. For example, the IV character curve of the load tube (that is, the load line) and the two output characteristic curves of the input tube are superimposed to obtain the output characteristic curve of the inverter and two operating points A and B, where A is the open state The operating point indicates the on-state of the inverter and outputs "0" level; B is the off-state operating point, which indicates the off-state of the inverter, and outputs "1" level.

E/EMOS倒相器工作

In summary, the saturated MOS inverter only uses one power source, has a relatively simple structure and is more convenient to use. But because the maximum output voltage can only reach VDD-VTL, The voltage is lower than the value of the voltage by one circle, and VS is not directly grounded, due to the backside gate effect, VT The value should be increased to reduce the output voltage amplitude. If it is required to output a higher high level. It is necessary to increase the power supply voltage, resulting in unnecessary power loss; moreover, because the load tube works in the saturation region, when the output is close to the high level value, the load tube is close to the cut-off state, and the resistance becomes very large, which is not good for the circuit speed. This will be analyzed below.

2、Unsaturated MOS phase detector

As mentioned above, although the saturated load MOS inverter has a simple structure, it has obvious shortcomings. In order to improve the performance of the inverter and increase the output voltage amplitude and working speed, the grid of the load tube of the inverter can be connected to a power supply VGS, Make the load tube work in the unsaturated zone. This kind of inverter is called a non-saturated load MOS inverter, as shown in Figure 2-9.

In order to make the load tube work in the unsaturated zone, it must meet:

E/EMOS倒相器工作