The attenuator is a management element, the principle operate of which is to cut back the energy of the sign passing by it. This sort of element is usually used to stability sign ranges within the sign chain, to increase the dynamic vary of a system, to offer impedance matching, and to implement varied calibration strategies in the long run utility design.
To proceed the collection of brief discourses on RF for non-RF engineers, we are going to focus on IC attenuators and provides some insights into their varieties, configurations, and specs. This text goals to help engineers with getting began with all kinds of IC merchandise and choosing the proper one for an finish utility. Associated articles on this collection embody: “A Information for Selecting the Proper RF Amplifier for Your Utility,” “How one can Simply Choose the Proper Frequency Era Part,” and “RF Demystified–Understanding Wave Reflections.”
Sorts of Attenuators
From the important thing practical perspective, attenuators might be categorised as mounted attenuators with an unchanging degree of attenuation and variable attenuators with an adjustable degree of attenuation. Relying on the type of attenuation management supported by variable attenuators, they will in flip be additional categorised as voltage variable attenuators (VVAs), that includes analog management, and digital step attenuators (DSAs) which can be managed digitally.
VVAs present steady adjustment of attenuation ranges that may be set to any worth inside the given vary. Analog variable attenuators are normally employed for automated achieve management circuits, calibration corrections, and different processing capabilities the place clean and exact management of a sign is required.
DSAs characteristic a set of discrete attenuation ranges permitting for sign energy changes with a predetermined attenuation step dimension. Digitally managed RFIC attenuators supply a management interface appropriate with microcontrollers and supply a great answer to keep up practical integrity in advanced designs.
Attenuator ICs might be realized in GaAs, GaN, SiC, or CMOS applied sciences utilizing resistors, PIN diodes, FETs, HEMTs, and CMOS transistors. Determine 1 reveals three primary topologies that underly varied varieties of attenuator design configurations: T-type, π-type, and bridged-T networks.
Determine 1. Primary attenuator topologies: (a) T-type, (b) π-type, (c) bridged-T networks.
Fastened worth attenuators make use of those core topologies realized with resistors in skinny movie and thick movie hybrid applied sciences to offer mounted ranges of attenuation.
VVAs usually use a T-type or π-type configuration with a diode or transistor components operated in a nonlinear resistance area. The resistance traits of the bottom components are exploited to regulate the required degree of attenuation by various the management voltage.
DSAs normally make use of a number of cascaded items representing particular person bits that may be switched in or out to realize the required degree of attenuation. A number of configuration examples used for DSA designs are proven in Determine 2. They embody configurations with built-in SPDT switches that toggle enter and output ports with the attenuating pad and a by line, switched-scaled machine designs with transistors or diodes used as switchable resistances, switched-resistor configuration the place the resistors might be switched in or out of the circuit, and device-embedded sort design with a transistor or a diode as an integral a part of the design.
Determine 2. DSA design configuration examples: (a) π-type configuration with built-in switches, (b) switched-scaled FET configuration, (c) switched-resistor configuration, (d) FET-embedded configuration.
Attenuator topologies might be organized right into a reflection- or balanced-type design schematically proven in Determine 3. Reflection-type gadgets use equal attenuators linked to the output of a 3 dB quadrature coupler and usually supply a big dynamic vary. Balanced configurations mix a pair of similar attenuators utilizing two 3 dB quadrature couplers and supply good VSWR and energy dealing with functionality.
Determine 3. (a) Reflection-type and (b) balanced-type attenuator design topologies.
Along with the principle design configurations described on this article, there are different varieties of circuits utilized for realization of IC attenuator elements; nonetheless, their consideration is past the scope of this brief article.1,2
To pick the suitable sort of an attenuator for the top utility, an engineer should have a great understanding of its key specs. Aside from the attenuation capabilities and a few basic parameters akin to insertion and return loss, there are different varied traits used to explain attenuator elements of which the important thing ones embody:
- Frequency vary (Hz): the frequencies over which the IC maintains its specified traits
- Attenuation (dB): the quantity of suppression in extra of the insertion loss
- Frequency response: variation of the attenuation degree (dB) throughout the frequency vary (Hz)
- Attenuation vary (dB): the whole worth of attenuation provided by the element
- Enter linearity (dBm): it’s normally expressed when it comes to the third-order intercept level (IP3) defining a hypothetical level for the enter energy degree at which the facility of the corresponding spurious elements would attain the identical degree of the elemental element
- Energy dealing with (dBm): it’s usually described when it comes to the enter 1 dB compression level defining the enter energy degree at which the insertion lack of the attenuator decreases by 1 dB; the facility dealing with attribute is commonly specified for the typical and peak enter energy ranges for the regular state and hot-switching modes
- Relative section (levels): a shift in section launched to a sign by the attenuator element
Along with these widespread parameters, variable attenuators are additionally described by their switching traits which can be usually expressed in ns when it comes to rise and fall time, on and off time, and the amplitude and section settling time of the RF output sign.
There are additionally particular traits inherent to every sort of variable attenuators.
For VVAs, they’re associated to their analog management operation and embody:
- Voltage management vary (V): the voltages required to regulate the attenuation degree inside the attenuation vary
- Management traits normally expressed when it comes to the attenuation slope (dB/V) and the efficiency curves displaying the extent of attenuation as a operate of management voltage
For DSAs, their inherent traits in flip embody:
- Attenuation accuracy (also called the state error) (dB): the restrict of variation within the attenuation degree relative to the nominal worth
- Attenuation step dimension (dB): the delta between any two successive attenuation states
- Step error (dB): the restrict of variation within the attenuation step dimension relative to the nominal worth
- Overshoot, undershoot (dB): the extent of sign transients (glitches) throughout state transitions
A superb attenuator element is usually required to ship flat attenuation efficiency and good VSWR throughout the operational frequency vary, to supply enough accuracy and energy dealing with functionality, and to make sure clean glitch-free operation with little sign distortions throughout state transitions or to offer linear management attribute.
The broad range of IC attenuator elements is actually not restricted to solely these mentioned on this article. We will acknowledge different varieties of ICs together with frequency-dependent and phase-compensated attenuators, temperature variable attenuators, programmable VVAs with an built-in DAC, and others. Nonetheless, on this article, we thought-about the commonest classes of IC attenuators in addition to mentioned their fundamental topologies and key specs, which will help an RF designer to decide on the suitable element for an finish utility.
Analog Gadgets offers the broadest portfolio of built-in RF elements within the business. ADI’s attenuators ICs can be found in a variety of architectures and kind elements, giving designers the pliability to pick out an element that greatest aligns with their system necessities. The elements are designed to supply the best-in-class efficiency and extremely dependable operation to deal with essentially the most demanding necessities throughout a variety of functions in instrumentation, communications, navy, and aerospace markets.