# 集成RF混频器与无源混频器方案的性能比较

Maxim的MAX9993高线性度下变频混频器具有图1所示功能：

MAX9993在PCS和UMTS频带的指标如下：
• 变频增益 = 8.5dB
• 噪声系数 = 9.5dB
• 三阶输入截点(IIP3) = +23.5dBm
• 三阶输出截点(OIP3) = +32dBm
• 二阶输入截点(IIP2) = +60dBm
• 二阶输出截点(OIP2) = +68.5dBm
• 低本振驱动电平：0到+6dBm
• 两路开关(SPDT)为GSM应用选择LO输入(本振开关在无切换应用重，如cdma2000®，选择固定本振信号)

G = 变频功率增益
NF = 噪声系数
IIP3 = 输入三阶截点
OIP3 = 输出三阶截点

G1 = -7.5dB
NF1 = 7.5dB (假设)
IIP31 = +29dBm
OIP31 = IIP31 + G1 = +21.5dBm

Gsys = 系统总增益 = +8.5dB
NFsys = 系统噪声系数 = 9.5dB
IIP3sys = 系统输入三阶截点 = +23.5dBm
OIP3sys = 系统输出三阶截点 = +32dBm

Gsys = 8.5dB
= G1 + G2由此解得G2
G2 = Gsys - G1 = 8.5dB - (-7.5dB)
= 16dB

NFsys = 9.5dB
= 10 * log (系统噪声系数)
= 10 * log (Fsys)
= 10 * log (F1 + (F2 - 1) / G1)

NF2 = 10 * log ((Fsys - F1) * G1 + 1)
= 10 * log ((10^(9.5 / 10) - 10^(7.5 / 10)) * (10^(-7.5 / 10)) + 1)
= 10 * log ((8.91 - 5.62) * 0.18 + 1)
= 10 * log (1.59)
= 2dB

IIP3sys (dBm) = +23.5dBm
= 10 * log (IIP3值)
= 10 * log (1 / (1/10^(IIP31 / 10) + 10^(G1 / 10) / 10^(IIP32 / 10)))

IIP32 (dBm) = 10 * log (10^(G1 / 10) * (1 / (1 / 10^(IIP3sys / 10) - 1 / 10^(IIP31 / 10))))
= 10 * log (10^(-7.5/10) * (1 / (1 / 10^(23.5 / 10) - 1 / 10^(29 / 10))))
= 17.5dBm

OIP32 (dBm) = OIP32 + G2
= +17.5dBm + 16dB
= +33.5dBm

1. Radio Concepts Analog by Ralph S. Carson, published by Wiley, 1990.
2. RF Design Guide Systems, Circuits, and Equations by Peter Vizmuller, published by Artech House, 1995.
3. MAX9993数据资料