Resistor Networks can be a good option for many applications, ranging from a simple power line transformer to complex high-speed data communications systems. The following article will discuss some of the characteristics of both wire-wound and thin-film resistors and R-2R ladder networks. It also explains the thermal impact and crosstalk of such systems. Resistor networks can be more efficient in certain conditions, while others may be less effective in others.
Wire-wound precision resistors
Typically, wire-wound precision resistors are made of constantan, manganin, or nichrome alloy wire. Some precision resistors are coated, and others are packaged in silicon resin. The latter has the advantage of preventing heat from escaping the product. As a result, these resistors have extremely low power dissipation. The benefits of wire wound precision resistors are numerous, and these products are ideal for a wide range of applications.
When choosing a precision resistor, it is important to pay attention to the precision specifications. Precision resistors should be accurate within ±0.01% at the factory and +/-300ppm after soldering them to the PCB. The reason is that resistance values will vary over time. Static electricity and humidity can cause the accuracy to decrease or increase. For this reason, stability is of utmost importance.
The temperature coefficient of resistance (TCR) is the variation in resistance concerning temperature change. The change can be ambient or self-generated. This variation is expressed in parts per million (PPM), percent, and O/O/deg C. The change in resistance is measured over a temperature range from +25 to 100 Deg C. TCPR is also useful in circuit simulation. However, it's essential to note that the temperature coefficient of resistance is not the same for every wire-wound precision resistor.
There are two types of wire-wound resistors: molded and through-hole. TCPR resistors have a molded surface mount (SMD) version, and coated through hole resistors are ideal for applications where the component must withstand short-duration impulses. Both types are available in a wide range of specifications and price ranges. TCPRs are also available in SMD Z versions.
Wire-wound precision resistor technology is one of the oldest types of precision resistors. They can reach resistance values of 50M. Temperature drift is typically less than one ppm/degC and accuracy is within 0.001%. The best wire-wound precision resistors are typically more expensive than other materials. Additionally, their high inductance and high resistance make them ill-suited for high-frequency circuits.
The main difference between wire-wound resistors and non-wire-wound resistors is the winding. The Ayrton-Perry winding has two wires that split at the resistance coil. They flow in opposite directions, and this reduces the chances of electron collisions. Unlike bifilar winding, Ayrton-Perry resistors have relatively low capacitance. As a result, they are suited for low-frequency and DC applications.
A wire-wound resistor has numerous advantages and disadvantages. This type of resistor is characterized by high blocking accuracy, low noise, and low-temperature coefficient. Although wire-wound resistors have largely been replaced by metal-film and oxide resistors, they remain popular in high-power circuits. They are also referred to as Nichrome resistors. You should note that wire-wound resistors are used primarily in power-related applications.
Thin-film resistors
A resistor network is constructed by connecting thin-film resistors. The thin-film resistor is produced in the form of a chip or SMD. Its axial leads enable it to be applied to a cylindrical base. It is more commonly used in precision controls and medical equipment. The difference between a thick-film resistor and a thin-film one is the amount of power they can handle.
Generally, resistor networks consist of one or more components. Thin-film resistors are made of a film that protects the resistor element. They are coated with tantalum oxide to provide a protective layer. Resistor networks are often packaged in DIL or DIP packages, with lead counts varying from 14 to 18 in DIL. SIP, or Single-In-Line Package, requires a much smaller building profile.
Resistance networks can be configured in an infinite number of ways. Unlike traditional wire-wound resistors, thin-film resistors can be bussed and arranged separately. Figures 13. to 18 illustrate common configurations. The resistor material determines the TCR and absolute tolerance of the network. Because parameters are standardized in a manufacturing batch, a tolerance can be set to ensure the accuracy of resistor values.
The resistance value of a rectangular film is characterized by the character of its lateral characteristics. The tab's resistance to the ground is maximum at the center of the film and decreases monotonically as the tab moves towards the ends of the film. The resistivity ratio of a rectangular resistive film is independent of its width, so the width must be kept small. This enables engineers to make complex resistive networks and devices with small space constraints.
An n-port monolithic thin-film distributed resistance network comprises a substrate wafer with a resistive film attached along the first boundary portion. The second boundary portion is substantially one-half the area of the film, with conductive tabs affixed along the other side. Both conductive tabs have a common fixed distance from a reference potential maintaining means. Thin-film resistors are a convenient way to build a resistive network.
As with traditional thick-film resistors, they can be easily screen-printed onto a polymeric substrate. The sheet resistivity of thick-film materials varies from 10 O/square to one MO/square. The resistance value desired is determined by the sheet resistivity. The thickness of the thin-film material may range from 0.5 to one mm. Thin-film resistors may also be screen-printed onto polymeric substrates.
An n-port thin-film distributed resistance network can be used for decoding digital signals. Compared to a conventional lumped resistance ladder network, the n-port thin-film resistance network does not require as many interconnected resistors. In addition to decoding analog signals, thin-film resistors can be used in a pulse code modulation receiver. They are especially useful for digital-to-analog decoders.
R-2R ladder networks
The basic structure of an R-2R resistor network shows the bits of information. Each bit is assigned a weight in the network. The output voltage Vout will depend on whether a bit is set to logic 1 or 0, depending on the type of technology used. The following diagram shows a simple R-2R network. The diagram shows that there are four resistors in the network and the total resistance is equal to the number of bits.
A four-bit asynchronous up counter contains a 74LS93 binary ripple counter. The outputs of the 74LS93 change by one step on each clock pulse. The input of an operational amplifier detects this change and outputs a negative voltage corresponding to the binary code at the R-2R ladder inputs. The currents are added together to give the overall voltage. Each bit changes a different amount.
The LSB part of an R-2R ladder is laser-trimmed, while the RSB portion does not. Trim tabs are required for the LSB section. Untrimmed resistors will increase chip area and increase chip cost. The "R" resistor circuits are laser-trimmable. They are available in a variety of resistor combinations. The R-2R ladder is designed to be versatile in applications ranging from RF to digital signal processing.
High-performance R-2R networks are made by assembling two or more resistors. These resistors share similar electrical characteristics and can be laser-trimmed. Resistor ladders have been used in analog-to-digital converters to increase precision. In the past, R-2R ladder networks were only used for signal conditioning, so there are plenty of applications for them. This article describes the main advantages of R-2R ladder networks.
The R-2R resistor ladder is the most widely used DAC. It uses two different values of resistors and is simple, accurate, and inexpensive. Most resistor component manufacturers manufacture monolithic R-2R resistor networks. It is a common choice in analog-to-digital conversion, as they require only two resistor values. The R-2R resistor ladder is the fastest DAC, and it can be used for many other applications.
While R-2R ladder networks are easy to implement, R-2R resistor networks are more popular. They are both effective as long as the resistors are close in resistance. R-2R-based DACs can be fabricated with minimal effort. It also has the advantage of being easier to implement than binary-weighted DACs. However, both R-based DACs have limitations. One design may be more stable than the other.
The MDAC can be implemented using an R-2R resistive ladder. The first "summing" conductor 11 supplies the output current to an operational amplifier 43. R-2R ladder networks can be the same as the ladder 10A of FIG. 2. For convenience, the ladder may comprise six "2R" legs. They are connected via a switch to a suitable reference voltage. In addition to improving the overall performance, R-2R ladder networks are also useful for a variety of other applications.
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