TTL and COMS

1. The upper and lower limits of the level are defined differently. CMOS has a greater anti-noise area. For a 5 V power supply, TTL is generally 1.7v and 3.5v, while CMOS is generally 2.2 V and 2.9v, which is not accurate and is for reference only.
2. The current driving capability is different. TTL generally provides 25 mA drive capability, while CMOS generally is around 10 mA.
3. The current input size is also different. Generally, TTL needs to be around 2.5 mA, and CMOS almost does not need current input.
4. Many devices are compatible with TTL and CMOS, and datasheet will explain. If you do not consider the speed and performance, General devices can be switched. However, you need to note that sometimes the load effect may cause the circuit to work abnormally, because some TTL Circuits need the input impedance of the next level as the load for normal operation.

(1) The TTL threshold level is relatively low and fixed, and the VCC change threshold level remains unchanged. The CMOS threshold level is VCC/2, which changes with the change of VCC.
Therefore, at the same time as the VCC, CMOS has a higher noise tolerance than TTL and strong anti-interference capability. (2) 4000 Series CMOS devices provide wider power supply range
(3) generally (VCC = 5 V) The CMOS logic circuit can directly drive the TTL logic circuit, while the TTL Logic Circuit
If you directly drive the CMOS logic circuit, the logic high level recognition error may occur. You need to adjust the output range of the logic level.
The TTL device operates at 5 V its output is Voh-3.6V Vol-0.2V. However, when the CMOS device operates 3-15 V, its output is voh = 0.7-0.8vcc and Vol = 0.2vcc.
The differences are as follows: TTL bipolar device, power supply voltage 5 V, fast speed NS, high power consumption MA level, high load capacity, Ma load, and no end-to-end processing. The CMOS Single-stage device and power supply voltage can reach 15 V, and the speed is several hundred ns. low power consumption, low power consumption, UA level, and low load capacity are measured by capacitive load, which must be processed by no end.
The Design of portable and battery-powered devices uses a CMOS chip. for high speed requirements, it is best to choose the 74sxxx series in TTL.
The 74hcxxx series is usually used for both speed and power consumption. Is an improved CMOS technology.

 

 

1, TTL Level:
The output level is greater than 2.4 V, and the output level is less than 0.4 V. At room temperature, the output high level is generally 3.5 V, and the output low level is 0.2 V. Minimum input height and low level: Input height> = 2.0 V, input low level <= 0.8 V, and noise tolerance is 0.4 V.
2, CMOS level: 1 logic level voltage is close to the power supply voltage, 0 logic level is close to 0 V. It also has a wide noise margin. 3. Level conversion circuit:
Because TTL The value is different from that of COMS ( TTL 5 V <=> CMOS 3.3 V), so the level conversion is required when the two resistors are connected to each other. There is nothing advanced. Haha 4, OC door, that is, open collector door circuit, OD door, that is, Drain open door circuit, must be open to the outside resistance and power supply to switch level as high and low level. Otherwise, it is generally used as the switch with large voltage and large current. Load , So it is also called the drive door circuit. 5, TTL Compared with the COMs circuit:
1) TTL The circuit is the current controller, while the COMs circuit is the voltage controller.
2) TTL The speed of the circuit is fast, and the transmission delay is short (5-10ns), but the power consumption is high. The speed of the COMs circuit is slow, and the transmission delay is long (25-50ns), but the power consumption is low. The power consumption of the COMs circuit is related to the pulse frequency of the input signal. The higher the frequency, the hotter the chip set.
3) coms circuit locking effect:
Because the input current of the COMs circuit is too large, the internal current increases sharply. The current keeps increasing unless the power supply is cut off. This effect is the locking effect. When the lock effect occurs, the internal current of COMS can reach more than 40mA, And the chip is easily burned out.
Defense measures: 1) Add a clamp circuit at the input and output ends so that the input and output cannot exceed the specified voltage. 2) The power input of the chip is coupled with a decoupling circuit to prevent high voltage at an instant on the VDD end.
3) adds a line resistance between the VDD and the external power supply, and does not let it in even if there is a large current.
4) when the system is powered separately by several power supplies, the switch should be enabled in the following order: when the power supply is enabled, the COMs circuit is enabled first, and then the input signal and Load Power supply; when off, first turn off the input signal and Load And then turn off the power of the COMs circuit. 6. Precautions for using the COMs Circuit
1) when the COMs circuit is used, the voltage controller has a high total input resistance and is capable of capturing interference signals. Therefore, do not leave unused pins empty. connect them to the pull resistance or drop-down resistance to give them a constant level.
2) When the input end is connected to a low internal signal source, a throttling resistor must be connected between the input end and the signal source so that the input current is limited to 1mA.
3) when the signal transmission line is connected to the COMs circuit, the resistance is matched.
4) when the input end is connected to a large capacitor, the resistance should be indirectly protected at the input end 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, coms may be burned out.
7, TTL Input end of door circuit Load Features (processing of input with resistance in special cases ):
1) when it is suspended, it is equivalent to when the input end is connected to a high level. It can be seen that the input end is connected to an infinite resistance.
2) input a low level after a 10 k resistor is connected at the input end of the door circuit. The input end shows a high level rather than a low level. Because TTL Input of door circuit Load It can be seen that only when the series resistance connected to the input end is less than 910 euros can the low-level signal input by the input end be recognized by the door circuit. If the series resistance is large, the input end remains high. Pay attention to this. The COMS door circuit does not need to consider this. 8, TTL The circuit has an open-collector OC gate, and the mos tube also has an open-drain OD gate corresponding to the Collector. Its output is called an open-drain output. The OC door has a leakage current output at the end, that is, the leakage current. Why is there a leakage current? That is because when the end of the three-host tube, its base current is about equal to 0, but it is not really 0. The current of the collector passing through the transistor is not really 0, but about 0. This is the leakage current. Open/leak output: the output of the OC gate is the open/leak output, and the output of the OD gate is also the open/leak output. It can absorb a large amount of current, but cannot output the current outward. Therefore, in order to be able to input and output current, it must be used together with the power supply and the pull-up resistor. The OD gate is generally used as an output buffer/driver, a level converter, and can meet the requirements of high absorption. Load Current needs.
9. What is the Tumen pillar? What is the difference between it and the open-leakage Road?
TTL In the integrated circuit, the output of a pulling transistor is called the tengzhu output, but not the OC gate. Because TTL It is a third-level customs, and the figure tengzhu is connected by two third-level tubes. So pushing and pulling is a totem. General Graphic Output, high 400ua, low 8ma