Figure 3: LTC5593 dual passive mixer in a receiver application Figure 1: Block diagram of dual-channel mixer


enabling the receiver to meet sensitivity and spurious requirements.


Another important performance target for multichannel receivers is the channel- to-channel isolation. The channel-to- channel isolation is the IF level at the undriven channel’s output relative to the IF level at the driven channel’s output. This parameter is usually specified to be 10dB better than the antenna-to-antenna isolation to avoid degrading system performance. Based on its precise IC design, the LTC5593 achieves 44dB of channel-to-channel isolation at 3.6GHz, and 52dB at 2.6GHz, which satisfies many multichannel application requirements.


Figure 2: LTC5593 LO return loss for different operating states


required external components to about 19, minimising board area, complexity, and cost.


Receiver application The functional diagram of an LTC5593 mixer in a two-channel receiver is shown in Figure 3. Single-ended RF signals are amplified and filtered before being applied to the mixer inputs. In this example, differential IF signal paths are shown, eliminating the need for an IF balun. The SAW filter, IF amplifier, and lumped-element bandpass filter are all differential. With the circuit


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component values as shown, this example receiver supports 150MHz IF bandwidth. Higher bandwidth can be achieved by lowering the resistance across the differential pins – with a slight reduction in gain. High-selectivity SAW filters are used in many MIMO receivers to block unwanted spurs and noise at the mixer output. The mixers’ 8dB of conversion gain compensates for the high insertion loss of these filters and reduces their impact on the system noise floor. The overall mixer performance allows the filter loss to be accommodated while


Power consumption and solution size With the maturing of multiband / multimode base station topologies and a more refined system definition migrating from 4G to the future 5G networks, wireless infrastructure systems are moving toward platform configurations that allow implementation of various band or mode requirements with minimal hardware and software changes. The LTC559x family of dual mixers all share a common pinout, making it easy to use the same board layout for all bands. The continued growth of wireless communications has also spurred the use of smaller cells such as picocells and femtocells. The need for more, and smaller cells, plus the increased use of remote radio heads has placed additional constraints on infrastructure systems, demanding higher integration and smaller solution size.


As the number of cells grows, power consumption has also become increasingly important as energy costs go up proportionally. In remote radio heads, on the other hand, thermal stress is a major concern due to reliance on passive cooling. Simply reducing the solution size is not sufficient, as reduced system size would result in higher power density, higher junction temperatures and potentially reduced component reliability. Thus, it is necessary to simultaneously reduce system power consumption and size. This goal is


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challenging, because the RF performance must not be compromised.


In the past, combining two individual mixers on one chip would result in total power consumption of 2 watts. To reduce power consumption, the LTC5593 family of mixers has been designed for 3.3V operation instead of 5V. Low voltage circuit design techniques reduce power dissipation without impacting conversion gain, IIP3 or noise figure performance. The only parameter affected by the lower supply voltage is the output P1dB performance, which is approximately 10.4dBm. The P1dB is limited by the output voltage swing at the open collectors of the IF amplifiers when driving the 200Ω load impedance. For applications where higher P1dB is necessary, the mixers have been specifically designed to allow the use of a 5V supply on the IF amplifier. The higher voltage improves the P1dB to 13.7dBm.


As shown in Table 1, the dual-mixers achieve excellent performance while using just over 1.3W of power, with both channels enabled. For additional power savings, each channel can be independently shut down as desired by using the independent enable controls. In instances where reduced linearity requirements are acceptable, the ISEL pin allows the user to switch to low current mode and further decrease DC power consumption.


Conclusion The LTC5593 dual passive


downconverting mixer delivers the high performance needed to meet the demanding requirements of emerging 5G multichannel infrastructure receivers, pushing higher frequencies and wider bandwidth. The mixer’s combination of high conversion gain, low NF, and high linearity improves overall system performance, and low power


consumption and small solution size meet the more stringent needs of ever-smaller base stations and remote radio heads.


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