Characteristics of CMOS integrated circuits and precautions for use

At present, digital integrated circuits can be divided into bipolar integrated circuits (mainly TTL) and unipolar integrated circuits (CMOS, NMOS, PMOS, etc.) according to the conductivity type. Single-gate static power dissipation in CMOS circuits is on the order of nanowatts (nw).

At present, digital integrated circuits can be divided into bipolar integrated circuits (mainly TTL) and unipolar integrated circuits (CMOS, NMOS, PMOS, etc.) according to the conductivity type. Single-gate static power dissipation in CMOS circuits is on the order of nanowatts (nw).

Introduction to CMOS Integrated Circuits

CMOS Complementary Metal Oxide semiconductor, a Voltage controlled amplifier device. It is the basic unit of CMOS digital integrated circuit.

Metal-Oxide-semiconductor (Metal-Oxide-semiconductor) transistors are referred to as MOS transistors, which are divided into P-type MOS tubes and N-type MOS tubes. An integrated circuit composed of MOS transistors is called a MOS integrated circuit, and a complementary MOS integrated circuit composed of a PMOS transistor and an NMOS transistor is called a CMOS-IC (Complementary MOS Integrated CIRcuit).

Performance characteristics of CMOS integrated circuits

Micro DC Power Dissipation – The static power dissipation per gate of a CMOS circuit is on the order of nanowatts (nw).

High Noise Tolerance – The noise margin of CMOS circuits is typically above 40% of the supply voltage.

Wide operating voltage range – The power supply voltage for CMOS circuits is typically 1.5~18 volts.

High logic swing – CMOS circuit outputs high and low level amplitudes to reach full voltage “1” is VDD, logic “0” is VSS.

High input impedance – The input impedance of CMOS circuits is greater than 108Ω, generally up to 1010Ω.

High Fanout Capability – CMOS circuits have a fanout capability greater than 50.

Low Input Capacitance – The input capacitance of CMOS circuits is generally not greater than 5PF.

Wide operating temperature range – The operating temperature range of ceramic package CMOS circuits is – 55 0C ~ 125 0C; plastic packaged CMOS circuits are C 40 0C ~ 85 0C.

All inputs have deletion protection circuit, good anti-radiation characteristics, etc.

Comparison of CMOS and TTL

CMOS developed later than TTL, but it has gradually replaced TTL in many occasions with its higher superiority. The following comparison of the performance of the two, we will know the reason.

1. CMOS is composed of field effect transistors, and TTL is composed of bipolar transistors

2. The logic level range of CMOS is relatively large (5~15V), and TTL can only work under 5V

3. The difference between the high and low levels of CMOS is relatively large and has strong anti-interference ability, while TTL has a small difference and poor anti-interference ability.

4. CMOS power consumption is very small, TTL power consumption is large (1 ~ 5mA/gate)

5. The operating frequency of CMOS is slightly lower than that of TTL, but the speed of high-speed CMOS is almost equivalent to TTL.

Precautions for the use of CMOS integrated circuits

1. CMOS circuit is a voltage control device, its input total resistance is very large, and its ability to capture interference signals is very strong. Therefore, the unused pins should not be left floating, and should be connected to a pull-up resistor or a pull-down resistor to give it a constant level.

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

3. When connecting a long signal transmission line, connect a matching resistor to the CMOS circuit.

4. When the input terminal is connected with a large capacitor, the resistance should be indirectly protected 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 CMOS exceeds 1mA, it may burn out CMOS.

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