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High precision and reliability (resistor)

This section introduces the application of resistors with highly accurate resistance value and temperature coefficient of resistance (T.C.R.), as well as the excellent long-term stability that contribute to high precision and reliability of equipment.
 

Higher precision amplifier circuit

The following figure shows an inverting amplifier circuit and a non-inverting amplifier circuit using an operational amplifier. The amplifier gain is determined by the ratio of R1 to R2. To achieve the required gain without any adjustment, resistors for R1 and R2 must have small resistance tolerance and T.C.R. Accordingly, the Metal Film Type Resistor RN73R, RN73H, the Wide Terminal Type Metal Film Flat Chip Resistor WN73H, and the High Reliability Chip Resistor RS73 series, are suitable. 
Network resistors, chip resistors incorporating paired resistors, work in this application as well. Building two resistors concurrently achieves excellent relative accuracy and T.C.R. In fact, KOA‘s Network Resistor, CNN2A, has two embedded resistors with the individual T.C.R. of ±25ｘ10-6/K, which is 5ｘ10-6/K or less in relative. In addition, KPC series has two or more resistors in one package, which enables better relative precision and high density mounting.
 

Low current noise

Noise of resistors are categorized into thermal noise or current noise.
 
Thermal noise is logically determined by resistance value, absolute temperature and frequency bandwidth, and has no relation with the resistor material.  In addition, the effective value in unit interval of frequency is extremely small and  distributed uniformly in the frequency domain, which leads to the main factor of deterioration of the S/N in broad band amplifier of wireless frequency. However, it doesn't normally pose any problems in the frequency range below the audio frequency.
 
On the other hand, current noise largely depend on the material, and becomes larger as the frequency lowers. In the frequency band below kHz, the effective value in unit interval of frequency is larger than the thermal noise; it increases incomparably especially in the frequency band below a few Hz.  For this reason, current noise is the main cause of S/N degradation, rather than thermal noise, in applications that handle low voltage near direct current, such as photo detector circuits (shown in the figure below) and electrocardiographs that amplify small detection signals with a large gain. In such applications, metal film resistors with low current noise, such as RN73R, RN73H, WN73H, MF, RNS are suitable.
 

Long-term stability

In circuits that detect voltage or determine the gain of an amplifier circuit, the resistance ratio initially set may fluctuate as the resistance value changes over time.

Generally, resistors formed of metal glaze or carbon film on resistive elements tend to degrade further than others. On the other hand, resistors formed of metal film on resistive elements degrade only a little and has an excellent long-term stability, making it suitable for the amplifier circuit described above. Recently, RS73 series that uses metal glaze as a resistive element yet has an excellent long-term stability, has been developed.

Therefore, RN73H, RN73R, WN73H, RS73, MF and RNS are suitable for applications that require the long-term stability of resistance value.
 

SMD(Surface Mount Device) Type

Item Series Product Name
Resistor RS73 High Reliability Chip Resistors
Resistor RS73-RT High Reliability Chip Resistors (Anti Sulfuration)
Resistor RN73H Metal Film Flat Chip Resistors (For Automotive, High reliability)
Resistor RN73R Metal Film Flat Chip Resistors (High reliability)
Resistor WN73H Wide Terminal Type Metal Film Flat Chip Resistors (High reliability)

Leaded Type

Item Series Product Code
Resistor RNS Coat-Insulated Precision Fixed Metal Film Resistors