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  • 7-bit 0.25dB Glitch-Free Wideband Digital Step Attenuator

  • Created: Aug 02, 2015

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Summary

This design is a 7-bit glitch-free wideband digital step attenuator with 0.25dB attenuation. An RF Attenuator is the opposite of an RF amplifier in that it reduces the amount of signal power in a system (i.e. attenuates the signal). Attenuation is required when the received signal level is too high that the system could not handle. The purpose of attenuation is to protect the circuit from receiving a significant amount of signal and to improve impedance matching.


This design features the Integrated Device Technology F1956, which offers very high reliability due to its construction from a monolithic silicon die in a QFN package. Also, the insertion loss is very low with minimal distortion. The device is designed to be extremely accurate which improves signal-to-noise ratio (SNR) and/or adjacent channel leakage power ratio (ACLR) by ensuring the system gain is achieved as close to target value as possible. Also, the settling time in parallel mode is very fast such that it is ideal for fast switching systems. The F1956 can be programmed using either the parallel or serial interface; selectable via VMODE pin 3. Serial mode is selected by floating VMODE (pin 3) or pulling it to a voltage > VIH and parallel mode is selected by setting pin 3 to logic LOW (0 V). Finally, the device is Glitch-Free with less than 2 dB of ringing across the attenuation range as compared to competing digital step attenuators (DSAs) that glitch as much as 10 dB during most significant bit (MSB) state changes.


This design is applicable to applications such as Base Station (BTS) radio cards, repeaters, point-to-point nodes and test-and-measurement equipment, and numerous other non-BTS applications. It can also be used for level control on the output of items such as signal generators since it is capable of generating 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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