在变频器应用的无源混频器

　　在变频器应用的无源混频器

　　而大多数的下变频混频器设计通常使用主动或电流整流的拓扑结构，新的无源混频器电路，可以提供更好的性能比线性显著。

　　无源下变频混频器的ltc554x家庭覆盖频率从600 MHz到4 GHz，并提供高转换增益和低噪声系数（NF）具有高线性度。这些混频器的目标是在无线基础设施接收器，需要高增益混频器，以克服高的插入损耗，今天的高选择性，如果SAW滤波器。而传统的无源混频器的变频损耗通常有7分贝，新ltc554x混频器集成中频放大器，如图1所示，产生整体转换增益8分贝。这允许一个额外的15分贝中频滤波器的损失，同时仍然使接收器。

　　Active versus passive mixers

　　Most integrated-circuit mixers are based on an active or current commutating topology. Linear Technology has a wide portfolio of active mixers， such as the LT5527 and LT5557， which are widely accepted due to their ease of use and low power consumption. Nevertheless， their 2 dB to 3 dB of conversion gain is not enough for some wireless infrastructure designs. Furthermore， active mixers typically exhibit higher NF than passive mixers with comparable linearity. LTC554x mixers employ a passive mixer core to achieve the lowest NF with high linearity. Table 1 compares the performance of the LTC5541 passive mixer to the LT5557 active mixer. As shown in the table， the passive mixer has approximately 5 dB higher gain， 2 dB lower NF， and 1.7 dB higher IIP3. The LT5557， however， has much lower DC power consumption.