Summary of TTL level and CMOS level

　　TTL level:

　　Output high level>2.4V Output low level<0.4V

　　At room temperature, the output high level is generally 3.5V and the output low level is 0.2V.

　　Minimum input high and low levels

　　Input high level >=2.0V Input low level <=0.8V

　　Its noise margin is 0.4V.

　　CMOS level:

　　The 1 logic level voltage is close to the power supply voltage, and the 0 logic level is close to 0 V. It also has a wide noise tolerance.

　　Level conversion circuit: Because the high and low level values ​​of TTL and COMS are different (TTL 5V "==" CMOS 3.3V), level conversion is required when connecting them to each other:

　　It is to use two resistors to divide the voltage level, nothing profound. Hahahaha

　　OC gate, that is, collector open gate circuit, it requires external pull-up resistor and power supply to use the switch level as high and low level. Otherwise, it is generally only used as a switch large voltage and

　　Large current load, so it is also called drive gate circuit.

　　Comparison between TTL and COMS circuits:

　　1. TTL circuit is a current-controlled device, while COMS circuit is a voltage-controlled device.

　　2. TTL circuits are fast and have short transmission delays (5-10ns), but they consume a lot of power.

　　The COMS circuit is slow and has a long transmission delay time (25--50ns), but has low power consumption.

　　The power consumption of the COMS circuit itself is related to the pulse frequency of the input signal. The higher the frequency, the hotter the chipset is, which is normal.

　　3. Locking effect of COMS circuit:

　　The CMOS circuit has a large input current, so the internal current increases sharply. Unless the power is cut off, the current continues to increase. This effect is called the locking effect.

　　When the lock effect occurs, the internal current of COMS can reach more than 40mA, which can easily burn the chip.

　　Defensive measures:

　　(1) Add clamping circuits at the input and output ends to ensure that the input and output do not exceed the specified voltage.

　　(2) Add a decoupling circuit to the power input terminal of the chip to prevent instantaneous high voltage from appearing at the VDD terminal.

　　(3) Add a line resistor between VDD and the external power supply to prevent large current from entering.

　　(4) When the system is powered by several power supplies, the switches should be turned on in the following order: when turning on, turn on the power of the COMS circuit first, and then turn on the power of the input signal and the load; when turning off, turn off the power of the input signal and the load first, and then turn off the power of the COMS circuit.

　　4. Precautions for using COMS circuits

　　(1) CMOS circuit is a voltage-controlled device with a large total input impedance and a strong ability to capture interference signals. Therefore, unused pins should not be left floating, but connected to pull-up or pull-down resistors to give them a constant voltage level.

　　(2) When the input terminal is connected to a low-input signal source, a current-limiting resistor should be connected in series between the input terminal and the signal source to limit the input current to within 1 mA.

　　(3) When extending the signal transmission line, connect a matching resistor at the end of the COMS circuit.

　　(4) When a large capacitor is connected to the input terminal, a protective resistor should be placed between the input terminal and the capacitor. The resistance value is R=V0/1mA. V0 is the voltage on the external capacitor.

　　(5) If the input current of COMS exceeds 1mA, it may burn out the COMS.

　　TTL level:

　　Output high level>2.4V Output low level<0.4V

　　At room temperature, the output high level is generally 3.5V and the output low level is 0.2V.

　　Minimum input high and low levels

　　Input high level >=2.0V Input low level <=0.8V

　　Its noise margin is 0.4V.

　　CMOS level:

　　The 1 logic level voltage is close to the power supply voltage, and the 0 logic level is close to 0 V. It also has a wide noise tolerance.

　　Level conversion circuit: Because the high and low level values ​​of TTL and COMS are different (TTL 5V "==" CMOS 3.3V), level conversion is required when connecting them to each other:

　　It is to use two resistors to divide the voltage level, nothing profound. Hahahaha

　　OC gate, that is, collector open gate circuit, it requires external pull-up resistor and power supply to use the switch level as high and low level. Otherwise, it is generally only used as a switch large voltage and

　　Large current load, so it is also called drive gate circuit.

　　Comparison between TTL and COMS circuits:

　　1. TTL circuit is a current-controlled device, while COMS circuit is a voltage-controlled device.

　　2. TTL circuits are fast and have short transmission delays (5-10ns), but they consume a lot of power.

　　The COMS circuit is slow and has a long transmission delay time (25--50ns), but has low power consumption.

　　The power consumption of the COMS circuit itself is related to the pulse frequency of the input signal. The higher the frequency, the hotter the chipset is, which is normal.

　　3. Locking effect of COMS circuit:

　　The CMOS circuit has a large input current, so the internal current increases sharply. Unless the power is cut off, the current continues to increase. This effect is called the locking effect.

　　When the lock effect occurs, the internal current of COMS can reach more than 40mA, which can easily burn the chip.

　　Defensive measures:

　　(1) Add clamping circuits at the input and output ends to ensure that the input and output do not exceed the specified voltage.

　　(2) Add a decoupling circuit to the power input terminal of the chip to prevent instantaneous high voltage from appearing at the VDD terminal.

　　(3) Add a line resistor between VDD and the external power supply to prevent large current from entering.

　　(4) When the system is powered by several power supplies, the switches should be turned on in the following order: when turning on, turn on the power of the COMS circuit first, and then turn on the power of the input signal and the load; when turning off, turn off the power of the input signal and the load first, and then turn off the power of the COMS circuit.

　　4. Precautions for using COMS circuits

　　(1) CMOS circuit is a voltage-controlled device with a large total input impedance and a strong ability to capture interference signals. Therefore, unused pins should not be left floating, but connected to pull-up or pull-down resistors to give them a constant voltage level.

　　(2) When the input terminal is connected to a low-input signal source, a current-limiting resistor should be connected in series between the input terminal and the signal source to limit the input current to within 1 mA.

　　(3) When extending the signal transmission line, connect a matching resistor at the end of the COMS circuit.

　　(4) When a large capacitor is connected to the input terminal, a protective resistor should be placed between the input terminal and the capacitor. The resistance value is R=V0/1mA. V0 is the voltage on the external capacitor.

　　(5) If the input current of COMS exceeds 1mA, it may burn out the COMS.

　　TTL level:

　　Output high level>2.4V Output low level<0.4V

　　At room temperature, the output high level is generally 3.5V and the output low level is 0.2V.

　　Minimum input high and low levels

　　Input high level >=2.0V Input low level <=0.8V

　　Its noise margin is 0.4V.

　　CMOS level:

　　The 1 logic level voltage is close to the power supply voltage, and the 0 logic level is close to 0 V. It also has a wide noise tolerance.

　　Level conversion circuit: Because the high and low level values ​​of TTL and COMS are different (TTL 5V "==" CMOS 3.3V), level conversion is required when connecting them to each other:

　　It is to use two resistors to divide the voltage level, nothing profound. Hahahaha

　　OC gate, that is, collector open gate circuit, it requires external pull-up resistor and power supply to use the switch level as high and low level. Otherwise, it is generally only used as a switch large voltage and

　　Large current load, so it is also called drive gate circuit.

　　Comparison between TTL and COMS circuits:

　　1. TTL circuit is a current-controlled device, while COMS circuit is a voltage-controlled device.

　　2. TTL circuits are fast and have short transmission delays (5-10ns), but they consume a lot of power.

　　The COMS circuit is slow and has a long transmission delay time (25--50ns), but has low power consumption.

　　The power consumption of the COMS circuit itself is related to the pulse frequency of the input signal. The higher the frequency, the hotter the chipset is, which is normal.

　　3. Locking effect of COMS circuit:

　　The CMOS circuit has a large input current, so the internal current increases sharply. Unless the power is cut off, the current continues to increase. This effect is called the locking effect.

　　When the lock effect occurs, the internal current of COMS can reach more than 40mA, which can easily burn the chip.

　　Defensive measures:

　　(1) Add clamping circuits at the input and output ends to ensure that the input and output do not exceed the specified voltage.

　　(2) Add a decoupling circuit to the power input terminal of the chip to prevent instantaneous high voltage from appearing at the VDD terminal.

　　(3) Add a line resistor between VDD and the external power supply to prevent large current from entering.

　　(4) When the system is powered by several power supplies, the switches should be turned on in the following order: when turning on, turn on the power of the COMS circuit first, and then turn on the power of the input signal and the load; when turning off, turn off the power of the input signal and the load first, and then turn off the power of the COMS circuit.

　　4. Precautions for using COMS circuits

　　(1) CMOS circuit is a voltage-controlled device with a large total input impedance and a strong ability to capture interference signals. Therefore, unused pins should not be left floating, but connected to pull-up or pull-down resistors to give them a constant voltage level.

　　(2) When the input terminal is connected to a low-input signal source, a current-limiting resistor should be connected in series between the input terminal and the signal source to limit the input current to within 1 mA.

　　(3) When extending the signal transmission line, connect a matching resistor at the end of the COMS circuit.

　　(4) When a large capacitor is connected to the input terminal, a protective resistor should be placed between the input terminal and the capacitor. The resistance value is R=V0/1mA. V0 is the voltage on the external capacitor.

　　(5) If the input current of COMS exceeds 1mA, it may burn out the COMS.