VAR Vishay Foil Resistors Ultra High Precision, Z-Foil Audio Resistor Minimizes Noise and Distortion in the Signal Path with TCR of 0.05 ppm/C, Tolerance to 0.005 % and High Linearity or Low Voltage Coefficient of Resistance (VCR) of 0.1 ppm/V FEATURES Temperature coefficient of resistance (TCR): 0.05 ppm/C typical (0 C to + 60 C,+ 25 C ref.) 0.2 ppm/C typical (0 C to + 125 C, + 25 C ref.) INTRODUCTION Rated power: to 0.4 W at + 70 C Many manufacturers and users of precision electronic Resistance tolerance: to 0.01 % (0.005% is available) equipment suffer needlessly from unexplained instabilities and drifts due to noise effects. They resign themselves to Load life stability: to 0.005 % at 70 C, 2000 h at rated making constant adjustments and troubleshooting. But in power fact these can be avoided. Instability is often traceable to a Resistance range: 10 to 100 k few supposedly fixed resistors which are not really fixed at all. If these resistors would only retain their original values, Naked Z-foil resisto design without molding or there would be no need for costly controls and other encapsulation adds an additional dimension for reducing compensating circuitry. Thats why the only resistor for signal distortion and increasing clarity in signal processing. applications such as these is Vishay Bulk Metal Foil. In Vishay Foil resistors are not restricted to standard values high-end audio equipment, careful selection of resistors is specificas-require values can be supplied at no extra one of the best ways to avoid or minimize noise and distortion in the signal path. Noise is an unwanted wide cost or delivery (e.g. 1K2345 vs 1K) spectrum signal that may be superimposed on any useful Electrostatic discharge (ESD) at least to 25 000 V signal, including DC. Resistors, like other passive Non-inductive, non-capacitive design components, are noise sources to various degrees, depending upon resistance value, temperature, applied Rise time: 1 ns, effectively no ringing voltage, and resistor type. Many experiments have been Current noise: 0.010 V (RMS)/Volt of Applied Voltage done to show why some resistors are noisier than others. (< - 40 dB) But the only test that audio experts and audiophiles have agreed on is comparing the level of fidelity that results when Thermal EMF: 0.05 V/C different resistor technologies are used in actual audio Voltage coefficient: < 0.1 ppm/V systems. Thermal stabilization time < 1 s (nominal value achieved High-end analog audio applications require low intrinsic within 10 ppm of steady state value) noise, high linearity of amplification, and minimal dynamic distortion. The typical audio amplifier consists of a voltage Inductance: < 0.08 H typical preamplifier (preamp) and power amplifier (final driver). The The Z-Foil chip in the VAR has been especially treated to voltage preamplifier deals with low-level signals. That is why increase load life stability. its intrinsic noise level is critical. Resistors are among the principal noise sources in the amplifiers. The main (1) Terminal Finish: lead (Pb)-free or tin/lead alloy requirements for the audio power amplifier are high linearity Prototype quantities available in just 5 working days or of amplification and minimal dynamic distortion. Vishay Foil sooner. For more information, please contact resistors are characterized by very low intrinsic non-linearity of the resistive element, which is made from cold-rolled bulk foil vishaypg.com metal. For better performances please contact us. The VAR, composed of Vishays Bulk Metal Z-foil technology, with improved sound quality, provides a combination of low noise and low inductance/capacitance, making it unrivalled for applications requiring low noise and distortion-free properties. Document Number: 63140 For any questions, contact: foil vishaypg.com www.vishayfoilresistors.com Revision: 03-Jan-12 1VAR Vishay Foil Resistors While the regular foil resistors are already widely Shot or fluctuation noise is caused by the discrete nature acknowledged as the leading resistors for audio applications, of charge carriers and fluctuation of their number in the unit the special naked Z-foil resistor design without mold or of volume. Shot noise can be reduced by reducing bandwidth encapsulation, adds an additional dimension for reducing or increasing current. The spectral density of voltage in both signal distortion and increasing clarity in signal processing. thermal and shot noises is uniformly distributed in entire Our application engineering department is available to range of frequencies (white noise). The level of these types advise and to make recommendations. For non-standard of noise does not depend on resistor type (resistive element technical requirements and special applications, please material). contact us. Current (excess, flicker) noise has 1/f type spectral density Bulk Metal Foil resistors owe their low current noise and high of voltage (pink noise). Its level essentially depends on linearity to the type of material theyre made of: a several resistor material. Current noise can be reduced by a) microns thick cold-rolled metal foil. Every real-world resistor avoiding use of the low frequency band, b) reducing current, possesses certain nonlinearity of its electrical resistance c) increasing the volume of resistive material, i.e. by using (nonlinearity of volt-ampere characteristic). The degree of resistors with higher rated power than is needed for proper nonlinearity depends on two factors: power dissipation, or d) using less noisy resistive materials. Micro factors: internal microstructure of resistive material. Carbon composition resistors are the noisiest such device type followed by Thick Film and Thin Film resistors. The least Macro factors (laser trimming cuts cleanness, micro noisy are bulk metals and metal alloys (foil, wire). At that, cracking in resistive element resulting from laser trimming, negligible capacitance/inductance of foil resistors (when quality of contacts between resistive element and compared to wirewound resistors) significantly reduces terminals, etc.). probability of self-excitation orringin of amplification circuit.This is why Bulk Metal foil resistors are such a good As for the microstructure, the most linear materials are pure choice for low-noise applications. metals and metal alloys in bulk, such as the foil in Bulk Metal Foil resistors. When the same materials are deposited in the form of very Thin (nanometer range) Films, they are less linear. Even less linear are composite materials FIGURE 1 - TYPICAL RESISTANCE / like resistive cermets in Thick-Film resistors or carbon TEMPERATURE CURVE compositions in carbon composition resistors. (Z-FOIL) The macro factors that cause nonlinearity in other types of TCR chord slopes for different temperature ranges resistors arent relevant to foil resistors. Indeed, laser + 500 trimming of foil resistors consists of cutting shorting jumpers + 400 + 300 and does not damage current carrying portions of resistive + 200 element. Terminals in foil resistors are an integral part of the + 100 R foil resistive element. This insures high-quality contact R 0 (ppm) between resistive element and terminals - 100 0.05 ppm/C - 200 - 0.1 ppm/C 0.1 ppm/C Several types of noise are found in resistors: - 300 0.14 ppm/C - 400 - 0.16 ppm/C 0.2 ppm/C Thermal noise is caused by thermal movement of electrons - 500 in resistive material and gets worse as resistance and - 55 - 25 0 + 25 + 60 + 75 + 100 + 125 temperature increase. Thermal noise can be reduced by Ambient Temperature (C) reducing resistance, temperature, or signal bandwidth. (2) TABLE 1 - RESISTANCE VERSUS TCR (- 55 C to + 125 C, + 25 C Ref.) RESISTANCE VALUE TIGHTEST TOLERANCE TYPICAL TCR AND MAXIMUM SPREAD (ppm/C) ( ) (%) 100 to < 100K 0.2 1.8 0.01 50 to < 100 0.2 2.8 0.01 10 to < 50 0.2 3.8 0.02 Note: (1) Pb containing terminations are not RoHS compliant, exemptions may apply (2) For non-standard requests, please contact application engineering at foil vishaypg.com www.vishayfoilresistors.com For any questions, contact: foil vishaypg.com Document Number: 63140 2 Revision: 03-Jan-12