Test Technology of Analog Integrated Circuits

With the advancement of integrated circuit manufacturing technology, people have been able to manufacture integrated circuits with quite complex circuit structures, high integration and various functions. However, these highly integrated, multifunctional integrated blocks are only connected to external circuits through a limited number of pins, which brings a lot of difficulties to judging the quality of integrated circuits. The 

idea of ​​compiling product test files is that 

test items, test conditions, and test specifications are generally called test files. 

Specific integrated circuits serve specific purposes, so the specifications of integrated circuits are proposed according to the requirements of user applications. Through discussions with users, we try to meet the needs of users according to the design and production capabilities, such as the power supply voltage range, input voltage, load size, packaging form, and application environment of the product proposed by users. 

Testing skills 

To complete the same test content, the methods and programs designed by different people will not be exactly the same, but a good solution should at least meet the following three requirements. The first is accurate testing, which is the minimum requirement, the second is good adaptability, and the third is that the program should save time when executed. 

Input adjustment method ` 

The input adjustment method is suitable for occasions where the output and input have a monotonically changing relationship, that is, for a certain output, only one input can be found that corresponds to it. This measurement requirement is needed in analog circuit testing. 

The input adjustment method actually uses the dichotomy method, that is, within the given input range, the first input determined is the median of the maximum and minimum, and the output at this time is measured and compared with the target value. In the case of positive polarity, if the measured value is greater than the target value, the second input value is the median of the median and the minimum value, and the output at this time is measured and compared with the target value. If the measured value is less than the target value, the third measurement value is the average of the median of the second input and the median of the first input (that is, the third median), and so on, until the target value is found. The 

above is about the positive polarity situation. The larger the input, the larger the output. For the negative polarity situation, the process of finding the predetermined point is just the opposite of the above. 

In summary, there are several elements to use the input adjustment method: a minimum input value; b maximum input value; c relationship between input and output; d predetermined output value; e maximum number of searches; f resolution. 

1. The so-called maximum number of searches refers to the maximum number of searches that the machine can perform according to a certain principle; the so-called resolution refers to the maximum allowable deviation between the output value and the target value, that is, how much the measured value is allowed to deviate from the target value before it can be considered that the adjustment requirements have been met. 

2. The "successive approximation method" is like a blind man climbing a mountain while judging while climbing. If the next step is higher than the previous step, continue to climb up. If you find a step lower than the previous step, stop climbing, indicating that the top of the mountain has been found. This is a figurative statement. For measurement, for a given input, the output is measured once, the input is changed according to a certain step length for the second time, and the output is measured again, and the cycle is repeated until the predetermined target value is found. 

3. Use a fast charging circuit to increase the test speed For audio devices, relatively large bypass capacitors are usually used, and these capacitors are usually connected to the high impedance circuit of the device under test. Therefore, it often takes a relatively long charging time to make the device under test reach a steady state. In order to shorten this process as much as possible and save test time, a fast charging circuit can be used. The so-called fast charging circuit is actually an impedance conversion circuit, which converts a high-resistance charging circuit into a low-resistance charging circuit, but does not destroy the original bias state of the circuit. 

4. Points to note when setting and measuring low-level signals 

Low-level signals include weak input signals, audio harmonic components (often encountered during distortion measurement), noise components, etc. Since these signals can almost be compared with the level of external noise, special attention should be paid when measuring such signals. 

a. 

The sensitivity of the TV IF circuit and the input limiting level of the audio IF circuit are generally only tens of microvolts to hundreds of microvolts. Such weak signals will be mixed with larger external noise when transmitted over a long distance. Therefore, when testing, a large signal is often set to the DUT board first, and then it is attenuated to a suitable level through the attenuator on the DUT board, so that the weak signal obtained is more stable. 

b. Noise measurement 

Noise is an unstable, random, weak signal. It fluctuates greatly with only a single measurement. Therefore, the average method of multiple measurements can be used for measurement, such as measuring 10 or 20 times, which will reduce the random error. In addition, an amplifier can be made on the DUT board to amplify the weak signal by 10 or 100 times before transmitting it to the machine for measurement. 

c. Points to note when testing distortion components The measurement of audio distortion usually measures the fundamental component first, then the harmonic component. By comparing the two, the distortion can be obtained. When measuring harmonic components, an amplifier is usually used to amplify the weak harmonic components as mentioned above. At this time, the appropriate amplification amount should be selected according to the maximum distortion component of the specification, so that even at the maximum distortion amount (i.e. the maximum harmonic component), it will not exceed the maximum allowable input value of the audio voltmeter in the machine.