Attenuator circuit

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Attenuator circuit

These RF attenuators can be fixed, switched or even continuously variable. There are many different types of RF attenuator, but the simpler ones using just resistors can be designed very easily, especially of they are for low power use.

As the name implies RF attenuators reduce the level of the signal, i. Typically the attenuation is defined in decibels, and fixed attenuators may be available in a variety of levels.

This attenuation may be required to protect a circuit stage from receiving a signal level that is too high. Also an attenuator may be used to provide an accurate impedance match as most fixed attenuators offer a well-defined impedance, or attenuators may be used in a variety of areas where signal levels need to be controlled.

There are many used for these RF attenuators and although these may not seem obvious initially when asking what is an attenuator, they are widely used in RF applications. Attenuators can be categorised in a number of ways according to their capabilities and the technologies they use:.

There are a number of ways in which attenuators can be designed and made. The two main types are given below. These are only broad categories for RF attenuators - they can be categories in a variety of ways according to the application and the type of attenuator technology that is used.

It is often necessary to show the block symbol in a circuits schematic diagram for an attenuator without necessarily showing all the individual components. RF attenuators are used in a wide variety of applications in RF circuits.

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They are a key building block used in many areas of RF design:. RF attenuators are used widely within RF circuits for a variety of reasons.

Fortunately these attenuators are easy to design and using surface mount technology their performance can be exceedingly good. An example of a small fixed attenuator with SMA connectors at either end What is an attenuator?

They may come in a variety of formats from small in-line items in a similar format to connector adaptors to those in small boxes with connectors on the ends to those incorporated within equipment. They are often seen as small boxes with a number of switches, typically with switches for 1, 2, 4, 8, etc dB changes.

Switched attenuators may also be found in items of test equipment to change the levels, for example of a signal generator output. Typically variable attenuators provide a continuous level change by varying an analogue voltage on the input control line. They are normally used where accuracy is not a prime requirement, but an analogue voltage is available - often in feedback loops controlling a level.

Levels may be varied by switching in different attenuator sections to provide the levels that are required.

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RF attenuator symbol It is often necessary to show the block symbol in a circuits schematic diagram for an attenuator without necessarily showing all the individual components. There is an attenuator symbol that has been widely adopted. Attenuator circuit symbol For some applications a variable attenuator symbol may be required: Variable attenuator circuit symbol RF attenuator applications RF attenuators are used in a wide variety of applications in RF circuits.

0 – 44 dB RF attenuator Schematic Circuit Diagram

This can be required to control levels within a circuit to keep them within the required range. One particular use is for testing high power RF signals, e. This can be very useful when driving RF mixers that are match sensitive and their performance will be degraded if a poor match is seen. It is far better to be able to generate an accurate fixed level from the basic generator and then used switch attenuators to reduce the signal to the required level.

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attenuator circuit

Selected Video 5G Cellular Communications - latest status. Featured articles.Attenuators are designed to change the magnitude of the input signal seen at the input stage, while presenting a constant impedance on all ranges at the attenuator input. A compensated RC attenuator is required to attenuate all frequencies equally. Without this compensation, HF signal measurements would always have to take the input circuit RC time constant into account.

The input attenuator must provide the correct sequence while maintaining a constant input impedance, as well as maintain both the input impedance and attenuation over the frequency range for which the oscilloscope is designed. The circuit diagram shown in Fig. The input impedance, as seen by the amplifier, changes greatly depending on the setting of the attenuator.

Because of this, the RC time constant and frequency response of the amplifier are dependent on the setting of th- attenuator, which is an undesirable feature. The diagram in Fig. The capacitive voltage dividers improve the HF response of the attenuator.

This combination of capacitive and resistive voltage dividers is known as a compensated attenuator. For oscilloscopes where the frequency range extends to MHz and beyond, more complex dividers are used. Figure 7. The input attenuator provides switching powers of 10, while attenuators at the output of the vertical preamplifier provides attenuation. Practically all oscilloscopes provide a switchable input coupling capacitor, as shown in Fig.

If a probe were connected to the oscilloscope, the input impedance at the probe tip would have a greater capacitance because of the added capacitance of the probe assembly and of the connecting shielded cable. If it is desired for HF oscilloscopes to have an input capacitance of much less than pf, an attenuator probe is used. This capacitor is adjusted so that the ratio of the shunt capacitance to the series capacitance is exactly 10 to 1.

The attenuator probe, often called a 10 to 1 probe, provides an approximately 10 to 1 reduction in the input capacitance. However, it also gives a 10 to 1 reduction in overall oscilloscope sensitivity. May 19, The resistive attenuator pads are very easy to design and can be incorporated into many RF circuits very easily. They reduce the level of the signal and this can be used to ensure that the correct radio signal level enters another circuit block such as mixer or amplifier so that it is not overloaded, and they are also used to ensure that a good impedance match is obtained.

Either Pi or T attenuator pads can be used and there is little to choose between them. Bridge T attenuator pads can also be used if required.

If the correct components and circuit techniques are used, then these attenuator pads can easily be used to operate at frequencies well into the GHz region. Surface mount resistors are particularly good, and modern PCB technology provides a good base for frequencies well above 1 GHz, although care may need to be taken when choosing the PCB material as some may be lossy and give the incorrect performance. Both the Pi attenuator pad format and the T attenuator pad format perform equally well.

Often the preference of which type to use is a matter of personal preference for the designer. The diagram below shows the format for the T attenuator pad format. As the name implies, the T attenuator pad is in the form of a letter T with two resistors in series in the signal line and a single resistor to ground at the junction of the two series resistors. The two resistor values can be calculated very easily knowing the ratio of the input and output voltages, Vin and Vout respectively and the characteristic impedance Ro.

The pi attenuator pad topology is in the form of the Greek letter pi and has one in line resistor and a resistor to ground at the input and the output. The bridged T attenuator can be used in a number of scenarios for which it provides some distinct advantages. The bridged T attenuator can be thought of as a modified Pi attenuator. The bridged T attenuator pad is often the favoured format for variable attenuators, especially those using PIN diodes.

The reason for this is that the bridged T attenuator pad only requires the use of two variable resistors against the three required for both the Pi and T attenuator pads. A further advantage is that as the bridged T attenuator pad has a tendency to match itself to the characteristic impedance Zo. At high attenuation levels R5 is at a high resistance and R6 is low. Accordingly the predominant resistor values at those labelled R which is equal to the characteristic impedance.

In many respects there is little difference between the pi and t attenuator pads. The choice of which type of pad to used often results from the preference of the design engineer. It may even result from the convenience of the values that result from the calculations. If the values from one type of attenuator pad fall conveniently close to standard values or those already in a design, then this may be a good reason for choosing "Pi" rather than a "T" attenuator pad or vice versa.

attenuator circuit

It has a single resistor to ground and has series resistors on the input and output, forming a T section. It has a single series resistor in the signal line and at the input and output a resistor is taken to ground.

T attenuator pad format The diagram below shows the format for the T attenuator pad format. Resistive T section attenuator pad The two resistor values can be calculated very easily knowing the ratio of the input and output voltages, Vin and Vout respectively and the characteristic impedance Ro.

Supplier Directory For everything from distribution to test equipment, components and more, our directory covers it. Selected Video What is an Oscilloscope - tutorial. Featured articles.This project arose from the fact that I had too much gain in my audio system, and I needed a practical solution without modifying the PCB circuit. Did you use this instructable in your classroom?

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Add a Teacher Note to share how you incorporated it into your lesson. There are very simple gadgets that can be used for audio purposes with great results. These are passive attenuators. They are very simple objects based on a resistive partition housed in male-female RCA connectors and can be used in particular when there are differences in sensivity between the source CD player, preamp, etc.

Despite the simple construction scheme, as I said before they can be quite expensive in the market. Before proceeding further, we have to remember that the audio signal can be distinguished substantially in two categories:.

The main difference between the two is that one is represented by an unshielded cable while the other does not. However, in reality the common RCA cable we use every day is made up of two conductors, one positive and one negative that also performs the shielding function against interferences provided that is not too long.

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The outer casing consists of two pieces of an aluminum tube that can be purchased in any hardware store. I bought one one meter long tube and with a diameter just slightly greather than the RCA internal screw.

Then I cut two equal pieces of cm long each. Then two wires cm in length are connected between the resistors and the terminals of the RCA connector. The two pieces can then also be painted at will as I did, by means of spray paint or left to its natural aluminium color. The first to the signal pin while the second in parallel from signal to ground pin. You can choose the female connector for this operation, but the reverse is also fine. It is advisable to cover bare wires and resistors with shrink tubing and insulating tape.

After this operation, the two resistors are interwoven and slightly soldered each other.

$100 Attenuator vs $500 Attenuator

At the end of the previous resistors, two electric wires cm long will be soldered and will then be connected to the ends of the other connector. At this point, the screw of each RCA connector is wound with the insulating tape so that it can fit perfectly inside the aluminum tube. A little of cyanoacrylic glue guarantees the seal of the connector to the tube. Once the operation is done on one, the next one will be to solder the wires to the terminals of the other connector.

Finally, the second screw of the connector is fastened to the tube, always with the help of a little glue. Question 2 months ago. Is there a simple formula for calculating the apparent load impedance seen by the source? In my case I'm trying to maintain an input impedance of 10K ohm or greater to my CD player, while cutting its output voltage by over half. My preamp claims to have a impedance of K ohms.

attenuator circuit

Question 10 months ago on Step 5. I'm thinking of getting an attenuator for an audio recorder plugged into a PA for live sound, but I don't know how many db I need. Maybe I need 10db or 20db - or something else. Would that make sense? It would likely be less compact, but that is not important to me. Answer 10 months ago. Hello, yes you can also a variable resistor.An attenuator is an electronic device that reduces the power of a signal without appreciably distorting its waveform.

An attenuator is effectively the opposite of an amplifierthough the two work by different methods. While an amplifier provides gainan attenuator provides loss, or gain less than 1. Attenuators are usually passive devices made from simple voltage divider networks.

Switching between different resistances forms adjustable stepped attenuators and continuously adjustable ones using potentiometers. For higher frequencies precisely matched low VSWR resistance networks are used. Fixed attenuators in circuits are used to lower voltage, dissipate power, and to improve impedance matching.

attenuator circuit

In measuring signals, attenuator pads or adapters are used to lower the amplitude of the signal a known amount to enable measurements, or to protect the measuring device from signal levels that might damage it. These may be required to be balanced or unbalanced networks depending on whether the line geometry with which they are to be used is balanced or unbalanced.

For instance, attenuators used with coaxial lines would be the unbalanced form while attenuators for use with twisted pair are required to be the balanced form. Four fundamental attenuator circuit diagrams are given in the figures on the left. Since an attenuator circuit consists solely of passive resistor elements, it is both linear and reciprocal.

If the circuit is also made symmetrical this is usually the case since it is usually required that the input and output impedance Z 1 and Z 2 are equalthen the input and output ports are not distinguished, but by convention the left and right sides of the circuits are referred to as input and output, respectively.

Various tables and calculators are available that provide a means of determining the appropriate resistor values for achieving particular loss values. Key specifications for attenuators are: [2]. Radio frequency attenuators are typically coaxial in structure with precision connectors as ports and coaxial, micro strip or thin-film internal structure.

Above SHF special waveguide structure is required. The size and shape of the attenuator depends on its ability to dissipate power. RF attenuators are used as loads for and as known attenuation and protective dissipation of power in measuring RF signals. A line-level attenuator in the preamp or a power attenuator after the power amplifier uses electrical resistance to reduce the amplitude of the signal that reaches the speaker, reducing the volume of the output. This section concerns pi-pads, T-pads and L-pads made entirely from resistors and terminated on each port with a purely real resistance.

The attenuator two-port is generally bidirectional.

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However, in this section it will be treated as though it were one way. In general, either of the two figures applies, but the first figure which depicts the source on the left will be tacitly assumed most of the time.

In the case of the L-pad, the second figure will be used if the load impedance is greater than the source impedance. The L-pad component value calculation assumes that the design impedance for port 1 on the left is equal or higher than the design impedance for port 2.Click here to go to our attenuator calculator.

Click here to go to our page on mechanically-adjustable attenuators new for June ! Reflection attenuators. Clifton Quan's patented attenuator.

Power dissipation in attenuators. Switchable attenuators. Switched-network attenuators.

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Switched-element attenuators. Digital attenuators stepped attenuators. RMS amplitude and phase of switchable attenuators. Variable attenuators. Ray Waugh's PIN diode attenuator. Attenuators are passive resistive elements that do the opposite of amplifiers, they kill gain. Why would you want to do that? Suppose your design specification calls for 10 dB gain, with a 1. You search the amplifier vendors, and locate an amplifier in your frequency band, but it has By adding an attenuator to the input, you can bring the gain down to 10 dB, and you will be improving the input match.

There are five common attenuator topologies used in microwave circuits, the tee, the pi, the bridged tee, the reflection attenuator and the balanced attenuator. The tee, pi and bridged tee each require two different resistor values, while the reflection and balanced attenuators need only a matched pair of resistors.

This allows both the reflection and balanced topologies to be used as variable attenuators with a single control voltage or control current. There are two variations of the reflection attenuator, depending on whether the terminations R 1 are less than or greater than the system characteristic impedance Z 0. When would you use a tee versus a pi versus a bridged tee? Here's some examples. When you are designing a fixed-value 3-dB attenuator on a thin film circuit, with a sheet resistivity fixed at ohms per square, the 8.

On the other hand, if your sheet resistivity was 10 ohms per square, you'd need 29 squares to create R 1 for the pi, and that might prove to be too inductive to work at high frequency.

With thick film circuits, you can take your pick because there are different resistivity values available. The bridged tee can be thought of as a modified pi network. Here are two reasons you might consider it over the pi. First, it only needs two variable resistors pi and tee need three.

Second, the bridged tee uses the full range of resistor values, from zero to infinity, for both R 1 and R 2. For the pi attenuator, R 1 never goes below Z 0 50 ohms so some of the diodes' useful resistance range is wasted.

Finally, the bridged tee has a tendency to match itself to Z 0 at high attenuation values, because of its two fixed resistors. In practice, the pi may give you higher attenuation range. The resistor R 2 can be a "sneak path" in the bridged tee because the diode or FET never reaches zero ohms.

The table below provides equations for solving for the attenuator resistive elements. It is incomplete; did you know that the tee and pi attenuators alone can have twelve forms of these equations, each? Think about this: there are four variables Z0, R1, R2, and dB and only two must be chosen to lock in the other two. Click on the calculator icon to check out our calculator where you'll be able to enter your desired attenuation parameters and we will calculate the resistors for you.

If you use the above equations to calculate R 1 and R 2be sure to observe whether "ATT" is divided by 10 or For those of you too busy or lazy to calculate your own resistor values, the table below should be useful Z 0 is assumed to be 50 ohms, but you can scale the values if necessary.We deliver up-to-date correct, authentic data based on evaluation unbiased at no cost to you.

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Anyone who has to reduce the amplitudes of RF signals in a controlled manner needs an attenuator. Linearly adjustable attenuation networks using special PIN diodes are available for this, but they require quite intricate control circuitry.

A simpler solution is to use an integrated attenuator that can be switched in steps. It can thus be used as an attenuator for cable television signals, for example. The attenuation can be set between 0 and 44 dB in 2-dB steps. An insertion loss of 4 dB must also be taken into account. This base attenuation can be measured in the 0-dB setting, and it forms the reference point for switchable attenuation networks that provide 2, 4, 8, 10 and 20 dB of attenuation.

These are all controlled by a set of 5 TTL inputs. The control signals must have Low levels below 0. A power-down mode, in which the current consumption drops to 0. The sample circuit diagram for the RF shows that the only external components that are needed are decoupling capacitors.

The table lists possible capacitor values. The input and output are matched to ohm operation, but they can also be used with ohm cables with a small increase in reflections. Its data sheet can be found at www.

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Homemade RCA Attenuator

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