In many electronic systems discrete resistor devices are more than adequate but when reliability and performance are of prime concern and space is limited a resistor network can be a better choice. Resistor networks offer a number of advantages including:
• Space Saving.
• Reduced resistor drift due to temperature and power variations.
• Lower cost.
• Improved System reliability.
Each of these issues is considered in more detail below.
A resistor device must be correctly packaged both for protection and to simplify the final system manufacturing process. This inevitably increases the overall size of the device but in a resistor network, there is only one packaging overhead rather than the two (or more) associated with discrete devices.
System board layout issues, minimum spacing and thermal issues can mean it is difficult to place discrete resistor devices in very close proximity but with a network, these issues are eliminated. This reduces the required system board area and simplifies the system manufacturing process.
Reduced Resistance Drift
The two main issues to consider are temperature co-efficient of resistance (TCR) and power coefficient of resistance (PCR). It is important to consider both but PCR tends to be more relevant in higher power resistor applications.
The proximity of external heat sources may impact on the resistance of one discrete resistor in relation to the other. Manufacturing variables in discrete resistors can also result is differences in self-heating effects again causing a variation in resistance between two discrete resistors.
The same change in temperature will, therefore, result in a different change in resistance between two discrete devices that can cause errors in a range of electronic circuits. Manufacturing resistor devices in close proximity, on the same substrate, using the same manufacturing process in a resistor network configuration resolves these issues.
It can often be cheaper to manufacture a single thick film resistor network than several discrete devices. A network can also simplify the system board layout and therefore reduce both the design time and system board cost.
Further savings may be made in inventory and qualification costs. It is often cheaper to stock and track a single network resistor device than several discrete components with different lot and part numbers.
As interconnect may be routed on the network substrate the amount of circuit board interconnect is reduced and the system reliability improved. There are fewer circuit board connections required with a resistor network than with multiple discrete devices as interconnections between resistors may be made on the substrate.
This further improves the circuit board reliability. When a designer decides a resistor network solution is the best way forward the issue can often be finding the required product among the standard product lines of the major resistor component manufacturers. If a standard product is not available then it is worth considering a manufacturer specialising in custom resistor network manufacture.