Four Techniques for Testing the Performance of Digital Integrated Circuits
1. Using the Voltage Method to Assess Digital ICs
1) If the supply voltage to the digital IC is normal and soldering is sound, but the measured voltage at the power supply pin is too low, the IC is likely damaged.
2) If the voltage at the power supply pin is normal but the voltages at most other pins are abnormal, this indicates a poor solder joint (cold solder joint) at the ground pin, while the IC itself is likely functional.
3) If the voltage at one or a few pins deviates significantly from the normal value, first check the associated peripheral circuitry for faults—such as short circuits or open circuits in resistors, or capacitor leakage or breakdown. If the peripheral circuitry is fault-free, the IC is likely damaged.
4) If the voltages at the majority of pins deviate significantly from normal values—despite normal supply voltage and sound solder joints at the power and ground pins—the IC is likely damaged.
2. Testing TTL Circuit Quality and Performance
Carefully identify the TTL IC model number and consult the relevant datasheet to locate the ground pin; ideally, obtain the internal circuit diagram or pinout diagram.
Set the multimeter to the R×1K range. Connect the black probe to the IC's ground pin and use the red probe to sequentially measure the DC resistance to ground for each input and output pin. Under normal conditions, the resistance to ground for each pin should be between 3 kΩ and 10 kΩ. If the resistance to ground for any pin is less than 1 kΩ or greater than 12 kΩ, the IC is damaged.
Connect the red probe to the ground pin and use the black probe to sequentially test each input and output pin. Under normal conditions, the reverse resistance to ground for each pin should exceed 40 kΩ. In contrast, the resistance to ground for the pins of a damaged integrated circuit is less than 1 kΩ. For a functional TTL circuit, the forward and reverse resistances to ground at the positive and negative power supply pins are lower than those of the other pins, with a maximum value not exceeding 10 kΩ. If this value is zero or infinite, the power supply pins of the integrated circuit are damaged.
3. Distinguishing between TTL and CMOS circuits using the voltage method
Distinction by model number: Models such as CC4000, CD4006, and MC14021 are CMOS circuits, whereas CT3020 and the 74 series are TTL circuits.
Distinction by supply voltage: If the specific model of a digital integrated circuit is unknown, it can be identified as a CMOS circuit if it operates correctly within the voltage ranges of 3–4.5V or 5.5–18V. Alternatively, a multimeter can be used to test the output levels. With a supply voltage of 5V, apply high and low logic levels to the circuit's input and measure the output with a multimeter; if the difference between the measured high and low levels is close to 5V, it is a CMOS integrated circuit, whereas a difference close to 3.5V indicates a TTL integrated circuit.
Distinction based on output voltage levels: Taking a simple gate circuit as an example, set the supply voltage to 5V and the multimeter to the 10V DC range. Apply high and low levels sequentially to the input and measure the corresponding output voltages. If the difference between these levels is close to 5V, it is a CMOS circuit; if the difference is close to 3.5V, it is a TTL circuit.
4. Distinguishing between CMOS circuits and high-speed CMOS circuits
Standard CMOS circuits operate on a supply voltage of 3–18 V, whereas high-speed CMOS circuits operate on 2–6 V. Therefore, if an integrated circuit functions correctly when a voltage of 2–2.5 V is applied, it is a high-speed CMOS circuit; otherwise, it is a standard CMOS circuit.
1) If the supply voltage to the digital IC is normal and soldering is sound, but the measured voltage at the power supply pin is too low, the IC is likely damaged.
2) If the voltage at the power supply pin is normal but the voltages at most other pins are abnormal, this indicates a poor solder joint (cold solder joint) at the ground pin, while the IC itself is likely functional.
3) If the voltage at one or a few pins deviates significantly from the normal value, first check the associated peripheral circuitry for faults—such as short circuits or open circuits in resistors, or capacitor leakage or breakdown. If the peripheral circuitry is fault-free, the IC is likely damaged.
4) If the voltages at the majority of pins deviate significantly from normal values—despite normal supply voltage and sound solder joints at the power and ground pins—the IC is likely damaged.
2. Testing TTL Circuit Quality and Performance
Carefully identify the TTL IC model number and consult the relevant datasheet to locate the ground pin; ideally, obtain the internal circuit diagram or pinout diagram.
Set the multimeter to the R×1K range. Connect the black probe to the IC's ground pin and use the red probe to sequentially measure the DC resistance to ground for each input and output pin. Under normal conditions, the resistance to ground for each pin should be between 3 kΩ and 10 kΩ. If the resistance to ground for any pin is less than 1 kΩ or greater than 12 kΩ, the IC is damaged.
Connect the red probe to the ground pin and use the black probe to sequentially test each input and output pin. Under normal conditions, the reverse resistance to ground for each pin should exceed 40 kΩ. In contrast, the resistance to ground for the pins of a damaged integrated circuit is less than 1 kΩ. For a functional TTL circuit, the forward and reverse resistances to ground at the positive and negative power supply pins are lower than those of the other pins, with a maximum value not exceeding 10 kΩ. If this value is zero or infinite, the power supply pins of the integrated circuit are damaged.
3. Distinguishing between TTL and CMOS circuits using the voltage method
Distinction by model number: Models such as CC4000, CD4006, and MC14021 are CMOS circuits, whereas CT3020 and the 74 series are TTL circuits.
Distinction by supply voltage: If the specific model of a digital integrated circuit is unknown, it can be identified as a CMOS circuit if it operates correctly within the voltage ranges of 3–4.5V or 5.5–18V. Alternatively, a multimeter can be used to test the output levels. With a supply voltage of 5V, apply high and low logic levels to the circuit's input and measure the output with a multimeter; if the difference between the measured high and low levels is close to 5V, it is a CMOS integrated circuit, whereas a difference close to 3.5V indicates a TTL integrated circuit.
Distinction based on output voltage levels: Taking a simple gate circuit as an example, set the supply voltage to 5V and the multimeter to the 10V DC range. Apply high and low levels sequentially to the input and measure the corresponding output voltages. If the difference between these levels is close to 5V, it is a CMOS circuit; if the difference is close to 3.5V, it is a TTL circuit.
4. Distinguishing between CMOS circuits and high-speed CMOS circuits
Standard CMOS circuits operate on a supply voltage of 3–18 V, whereas high-speed CMOS circuits operate on 2–6 V. Therefore, if an integrated circuit functions correctly when a voltage of 2–2.5 V is applied, it is a high-speed CMOS circuit; otherwise, it is a standard CMOS circuit.
Sep 10,2026