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用于直播卫星接收机中的12GHz频段GaAs双栅MESFET单片混频器已经研制成功。为了减小芯片尺寸,缓冲放大器直接连在混频器的中频输出端后面,而不采用中频匹配电路。混频器和缓冲器制作在各自的芯片上,以便能分别测量。混频器芯片尺寸是0.96×12.6mm,缓冲器芯片尺寸是0.96×0.60mm。用于混频器的双栅FET和用于缓冲器的单栅FET都具有间隔紧密的电极结构。栅长和栅宽分别是1μm和320μm。带有缓冲放大器的混频器在11.7～12.2GHz射频频段提供2.9±0.4dB变频增益和12.3±0.3dB单边带(SSB)噪声系数。本振频率是10.8GHz。将一个单片前置放大器、一个镜象抑制滤波器和一个单片中频放大器与混频器连接起来构成低噪声变频器。变频器在上述频段内提供46.8±1.5dB的变频增益和2.8±0.2dB单边带噪声系数。
A 12GHz band GaAs dual-gate MESFET monolithic mixer for direct broadcast satellite receivers has been developed. In order to reduce the chip size, the buffer amplifier is connected directly to the IF output of the mixer, without the IF matching circuit. Mixers and buffers are fabricated on separate chips so that they can be measured separately. The mixer chip size is 0.96 × 12.6mm and the buffer chip size is 0.96 × 0.60mm. Double-gate FETs for mixers and single-gate FETs for snubbers have closely spaced electrode structures. The gate length and gate width are 1 μm and 320 μm, respectively. The mixer with buffer amplifier provides 2.9 ± 0.4dB conversion gain and 12.3 ± 0.3dB single sideband (SSB) noise figure in the 11.7-12.2GHz RF band. The local oscillator frequency is 10.8GHz. A monolithic preamplifier, an image reject filter, and a monolithic IF amplifier are connected to the mixer to form a low-noise inverter. The inverter provides 46.8 ± 1.5dB of variable frequency gain and 2.8 ± 0.2dB single sideband noise figure in the above frequency bands.