Coexist with a wide variety of communication standards , more and more wireless communication devices need to meet multi-band, high-bandwidth requirements that the system design, especially RF circuit design brings a great challenge. Subject to the constraints of semiconductor technologies and RF technology itself is complex, high-performance , broadband radio frequency integrated circuit design is usually very difficult to achieve , RF devices on to meet the high bandwidth, low noise , spurious-free dynamic range and other key technical indicators often inadequacy . And one of the key components as the RF mixer circuit design , no doubt is a typical representative .
Engineers are usually familiar with RF circuit understand two terms - active mixers and passive mixers. Due to the inherent characteristics of the two mixer architecture , active mixers usually means high bandwidth , and is almost identical to the passive mixer low bandwidth mixer. However , mixers , high-bandwidth and high-performance technology seems inherently can not have both fish and bear little embarrassing - active mixer generalities spurious-free dynamic range and linearity features let in a lot of right performance for demanding broadband applications eclipsed , while passive mixers despite spurious-free dynamic range characteristics , linearity next obvious advantages , but low-bandwidth prohibitive. However, in applications such as cellular base stations , the poor working conditions and changing market structure requires the receiving device has a high performance , high bandwidth in order to meet the design requirements , most have adopted a good average of bandwidth but other performance indicators the active mixer . Such a compromise is no doubt there are some performance problems, such as a higher rate of dropped calls .
In a typical application of multi-band wireless communication system / multi-standard cellular base station receivers, wideband radio link inverter, multi-mode cellular repeaters , and picocells applications , if you want to take advantage of the above-mentioned advantages of passive mixer characteristics , the usual solution is to use a plurality of narrow-band mixer. ADI three companies use innovative technologies to improve the effective lifting of the passive mixer bandwidth "curse" , recently launched the industry's first wideband passive mixer frequency range --ADL5811/5812, 700MHz to 2800MHz for , so that the traditional need three passive mixer RF front-end circuits can be realized only a single chip , greatly simplifying system design and improve RF circuit performance ( see Figure 1 ) .
Three innovative technology breakthroughs passive mixer narrowband "fate "
ADL5811/5812 passive mixer eliminates broadband applications has been selected in the active or passive mixer must face the embarrassment of a compromise , because they are not only able to provide engineers need linearity, distortion and noise performance , and support wideband frequency operation in the true sense . The new ADI passive mixer in a single device supports wide frequency range of 700MHz to 2800MHz , the input IP3 ( TOI ) is 24 dBm, SSB noise figure of 11dB, power conversion gain of 7dB. ADL5811/5812 achieve the industry's best linearity, noise figure, spurious-free dynamic range and blocking performance , and these performance specifications remain stable over the entire operating frequency range.
The new passive mixers , thanks to the outstanding performance of the three techniques ( Figure 2 ) : Broadband , limiting LO amplifier ; programmable RF balun transformer ; programmable low -pass filter. Among the most prominent is the broadband square wave limiting LO amplifier with traditional narrowband sine wave LO amplifiers, allowing the higher or lower than the RF input LO applied extremely wide bandwidth , this amplifier can of 250MHz to 2760MHz produce a faster pressure rise time of the square wave in the higher bandwidth and does not cause a DC current to rise . Which is typically a passive mixer narrowband insurmountable problems . Moreover , since no energy storage element , and therefore also with the LO frequency DC power decreases.
Previously, narrowband mixers integrated one kind of magnetic or RF transmission line balun transformer constituted , limited bandwidth greatly limits the application of this type of mixer . ADL5811/5812 industry's first innovative use of programmable RF balun transformer structures to ensure a balanced RF signal is loaded into the FET mixer , can enter the frequency range to achieve the best performance in the 700 MHz to 2800 MHz RF, in provide excellent throughout the RF bandwidth to the RF and LO LO to IF leakage , excellent RF to IF isolation and excellent intermodulation performance. The third innovation ADL5811/5812 is used the output of the mixer incorporates a programmable low -pass filter, low pass filter to filter out unwanted sideband signal to remove unwanted sideband signals caused by the IF amplifier premature compression , which can improve the linearity. ADI design a tunable filter network to provide an appropriate frequency side ( as a function of RF and LO frequencies ) , thereby reducing the load of the unwanted sideband amplitude.
Three main technical progress achievements in high-performance broadband passive mixers : a broadband , limiting LO amplifier ; 2 programmable RF balun transformer ; 3 programmable low -pass filter . . innovative design mixer mixer allows more secure
In addition , ADL5811/5812 used balanced mixer core also provides extremely high input linearity, so that the family of devices can be used in demanding broadband applications. For these applications, if the input is not high linearity , band blocking signals may lead to reduced dynamic range . Balanced mixer core implemented blocking noise figure performance and design is quite narrow-band passive mixer . On ADL5811/5812, immediately after the passive mixer core , using a high linearity IF buffer amplifier , which provides 7 dB typical power conversion gain , and can be used with a variety of output impedance.