1. PMOS and NMOS diagrams, MOS tubes are also called field effect tubes, that is, insulating field effect tubes in integrated circuits. The full name of MOS in English is Metal-Oxide-Semiconductor, that is, Metal-Oxide-Semiconductor. To be precise, this name describes the structure of MOS tubes in integrated circuits, that is, silicon dioxide and metal are added to semiconductor devices with a certain structure. , forming a gate. The source and drain of the MOS tube can be reversed, and they are all N-type regions formed in the P-type backgate.
There are three pins of the MOS tube: source S (source), gate G (Gate) and drain (Drain)
source: it is the source, the source, so the current should go from the source to other places, where Woolen cloth? It is the drain, definitely not the gate, because the gate is the control pole, a pole that gives orders, so the performance should be the source and drain. In this way, the gate is the director, and the source and drain are actors, but the source is the leading role and the drain is the supporting role. These three roles play their respective responsibilities on the stage of MOS
There are two types of MOS tubes: one is a PMOS tube and the other is an NMOS tube; the PMOS tube is a positive tube, which is a positive tube, and the NMOS tube is a negative tube, which is a negative tube. Positive management is to follow the trend and go with the trend; negative management is to go against the trend and go against the current. Obviously, if the current flows from the source (input terminal) to the drain (output terminal), it follows the trend, because the source is the source, so this kind of tube is a PMOS tube; and if the current flows from the drain (input terminal) To the source (output terminal), that is upstream, it is the NMOS tube
The gate is also the gate, since it is a gate, it has the function of control
Whether it is a PMOS tube or an NMOS tube, we only need to compare the relationship between the G pole voltage and the S pole voltage to judge whether the MOS tube can be turned on.
For PMOS tubes, the current is from the source (input terminal) to the drain (output terminal), from top to bottom, the level of each node should be gradually reduced, so the voltage of the gate G must be less than the source voltage ; In other words, when UGS<0, the PMOS tube is turned on.
For NMOS tubes, the current is from the drain (input terminal) to the source (output terminal), from bottom to top, the level of each node should be gradually reduced, so the voltage of the gate G must be greater than the source voltage ; In other words, when UGS>0, the NMOS tube is turned on.
NMOS is turned on at a high level (VGS > Vt) at the gate, and turned off at a low level, which can be used to control the conduction between the gate and the ground.
PMOS is turned on at a low level (VGS < Vt) at the gate, and turned off at a high level, which can be used to control the conduction with the power supply.
The characteristics of NMOS, when Vgs is greater than a certain value, it will be turned on. It is suitable for the situation when the source is grounded (low-side drive), as long as the gate voltage reaches 4V or 10V.
The characteristics of PMOS, Vgs is less than a certain value will be turned on, suitable for the situation when the source is connected to VCC (high-end drive), but although PMOS can be easily used as a high-end drive, but due to the large on-resistance, the price Because of the high cost and few replacement types, NMOS is usually used in high-end drivers.
NMOS is turned on at a high level (|VGS| > Vt) at the gate, and turned off at a low level, which can be used to control the conduction between the gate and the ground. PMOS is turned on at low gate (|VGS| > Vt) and disconnected at high level, which can be used to control the conduction with the power supply.
For NMOS, the Source terminal is generally grounded (low potential), so if |VGS| > Vt, the Gate terminal must generally be connected to a positive voltage, so that the tube can be turned on; for PMOS, the Source terminal is generally connected to
VDD (high level), so it must be Let |VGS|>Vt, then the Gate terminal generally needs to be connected to a negative voltage (lower than the voltage of VDD), so that the tube can be turned on
2. The method of judging NMOS and PMOS
According to the direction of the PN junction of the substrate, the PN junction pointing inward is the NMOS transistor, and the PN junction pointing outward is the PMOS transistor.
3. Application of PMOS and NMOS
(1). The following figure shows the separation circuit of USB OTG power management.
The analysis is as follows
. Assume that there is no voltage on the left side, and the right side is 5V
U14. Because the right side current cannot flow into the left side;
assuming that the left side is 5V, there is no voltage on the
right side U14.
is 5V, and the right side is 5V.
The left triode of U14 is turned on and the right triode is turned on, causing the Q3 PMOS tube to be turned off. As a result, there is no current flow on the left and right sides;
