Linear Technology’s dual downconverting mixer

Linear Technology’s dual downconverting mixer

On June 8, 2011, Linear Technology introduced the LTC5569, a dual high-performance RF mixer that packs a combination of 26.8-dBm IIP3 (input third-order intercept), 300 mW per mixer, and wide operating frequency coverage to address high density footprints of multimode 4G RRH (Remote radio head) MIMO (multiple-input, multiple-output) receivers. There was a need for this type of product.

Electronic Products Technical Editor Jim Harrison presents award to Linear Technology Product Marketing Manager James Wong.

James Wong, Product Marketing Manager at Linear Technology, commented: “Our customers were building basestation receivers with diversity and MIMO capabilities which required dual or parallel receive paths. Furthermore, the MIMO receivers required a phase-coherent local oscillator (LO) delivered to each mixer, which was difficult to achieve with their current method of using individual (single) mixers for each receive path. These customers were already using our low-power active mixers in their receivers, and they were opposed to using the high-power dual passive mixers that just became available from our competitors. To address this need in the market, we went to work on a very compact dual active downconverting mixer, the LTC5569. This dual mixer is packaged in a small 4 x 4-mm plastic QFN package and requires very few external components. Furthermore, the power consumption is only 45% of the power consumption of a comparable dual passive mixer.”

Challenges

The biggest challenges were designing for high-channel isolation between the two mixers on one common die, and improving second-order distortion. Both of these performance parameters are difficult to simulate and required significant experience and skill in the design and layout phase. The LTC5569 delivers greater than 40-dB channel isolation up to 3 GHz, a significant accomplishment considering the small package and compact board layout. Furthermore, the second-order distortion was 20 dB less than our previous (single) active mixer.

About the team

According to Mr. Wong, “In the initial planning phase, the team involved Design and Marketing who reviewed our concept with customers. In the design phase, we were fortunate to have one of the best IC layout engineers in our company, which played an important role in the success of the channel isolation. Finally, Product and Test Engineering resolved the challenges of testing and producing the two mixers in one package.”

Christina Nickolas