F1950 - 7-bit 0.25 dB Glitch-Free™ Digital Step Attenuator

This reference design features the F1950 digital step attenuator. It is a 7 bit step attenuator optimized for applications such as base station radiocards, repeaters, digital pre-distortion, WIMAX transmitter/receiver, RFID handheld, etc. The F1950 attenuator device has a pinpoint accuracy and can settle to an attenuation value in just a matter 400ns. The glitch-free technology included in the design of F1950 attenuator enables the device to switch to its maximum/minimum attenuation value with just a 0.6dB transient overshoot. The device has a very low insertion loss which makes it ideal for applications demanding best signal to noise ratio.

The main supply for the F1950 device ranges from a 3V to 5.25V with a current consumption of 0.25mA. The radio frequency that it can attenuate ranges from 150MHz-4000MHz. To adjust the attenuation value of this device, either of the pins D0-D6 must be pulled to HIGH or LOW depending on the value of attenuation required. The minimum attenuation value that this device can offer when all pins are LOW is around 1.3dB while the maximum attenuation value is 33.0dB when all pins are set to HIGH. The device can operate in two control modes, serial or parallel control mode. The serial mode is selected by floating the VMODE pin of the device or pulling it to a logic input HIGH while in parallel control mode, the user is left with options of running it in direct or latched parallel mode. The direct parallel mode is selected when the VMODE pin is pulled LOW and the LE pin of the device is pulled HIGH while latched parallel mode is selected by pulling VMODE pin LOW and toggling LE pin from HIGH to LOW. In direct parallel mode, the device will react immediately to any changes in the control pins D0-D6 unlike in latched parallel mode that the device will not change its attenuation value unless the LE pin is pulled HIGH.