HMC472a , HMC1122 , HMC624

Question

Hello, 
 We are going to buy a DSA evaluation board. I am beginner with these stuff... We are between HMC472a , HMC1122 & HMC624a. 
 1) Could you please help choosing? Which DSA is best for our specifications? We will buy the evaluation board of one of these DSA's. We work @2.4GHz and we need fast settling time (That's why all will be working in parallel mode). We are working in 11MHz clock. 
 2) Can the parallel pins be controlled from FPGA pins? We are going to connect this DSA evaluation board with FPGA ( Probably LVCMOS or LVTTL 3.3V , is it ok? ). Do they need common ground or is it ok to supply directly from the FPGA Bank Output Pins? 
 3) What are the Switches intended for in evaluation boards? Do Direct/Latched modes are related to Switches or not? Manuals refer: "Directed Parallel Mode is ideal for manual control of the attenuator". Does manual means with Switches and only Latched can be used with real-time digital control via FPGA? 
 Thanks in advance, 
 Theo

hkumar · Accepted Answer

Hi THKont, 
 These attenuators can be controlled in many ways: - Direct Parallel Mode : In this mode, the voltages are applied to the parallel control pins (D0 to D5). Any changes to the parallel control voltages is directly applied to the RF transistors and results in an immediate change to the state of the attenuator. For easier debugging of boards, often times the DSA are configured in direct parallel modes and the parallel control pins are connected to mechanical switches. You can omit this and connect to the FPGA - the applications section of the datasheet has more information on how to do so. - Latched Parallel Mode : In this mode, the voltages are applied to the parallel control pins (D0 to D5), and then a LE (latch enable) pulse is applied. Only when the LE pulse is applied, the voltages is transferred to the RF transistors and the state of the attenuator changes. - Serial Mode : Some attenuators have an integrated SPI controller that supports a 4-wire SPI protocol. You can use SERIN, LE, CLK, SEROUT to control the state of the attenuator. 
 All of the attenuators you list above will work for your application. Due to the inherent gate-lag effect of the GaAs process, the Silicon digital attenuators typically have a faster RF settling time. The HMC1122 looks like the best fit for your application. This attenuator typically settles to 0.1dB of the final RF value in 200ns. The RF settling time should be the same regardless of the mode of operation (assuming the control pulses themselves are fast enough). 
 Please refer to the Electrical Specifications table of the datasheet to determine if the part is compatible with LVTTL controls. This is specified in the Digital Control Inputs section. 
 Curious - what application is this for? Please let me know if you have any other questions. 
 Thanks, HK.

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Products In This Thread

HMC472a , HMC1122 , HMC624

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