# 混频器2x2杂散响应与IP2的关系

### 混频器的谐波

fIF = ±fRF ± fLO

fIF = ±m fRF ±n fLO

### 半中频杂散产物的分布

• fRF = 1950MHz
• fLO = 1750MHz
• fIF = 200MHz
• 计算：fHalf-IF = fRF – fIF/2 = 1850

2 × fHalf-IF – 2 × fLO =
2 × (fRF - fIF/2) - 2 × (fRF - fIF) =
2 × fRF – 2 × fIF/2 - 2 × fRF + 2 × fIF = fIF

2 × 1850MHz – 2 × 1750MHz = 200MHz

### 接收机的IP2

2x2杂散响应的抑制度，可以从混频器的IP2指标推导。当定义混频器的IP2或者2x2特性时，一般假定仅RF和LO的基波成分注入混频器端口并且谐波失真仅是由混频器自身产生的。RF通道中混频器前端的镜频抑制滤波器可以衰减掉任何放大器的谐波成分。在LO通路中的噪声衰减器可以衰减掉LO通道中的信号源产生的谐波成分。高电平的注入信号会产生失真或者互调产物，无论是在系统或器件的输入或输出端1，这些产物可以通过计算交调点进行量化。输入交调点为假定所需信号的幅度与不希望产生的谐波成分幅度相同时的输入信号幅度。这种情况下混频器的LO输入保持恒定不变，交调点的阶数或者失真产物仅由RF的乘数而不是LO的乘数决定，这是因为我们仅考虑RF信号的失真变化。失真产物的幅度随着输入信号幅度增加的快慢由失真信号的阶数决定。例如，当输入信号的幅度增加1dB时，2阶互调(IM)产物的幅度会增加2dB。

### 半中频杂散功率电平

• 在1840MHz时的RF杂散电平设定为-5dBm.
• 在1750MHz，LO的电平设定为+6dBm.
• 测量到的典型2RF – 2LO杂散响应低于RF载波电平70dB，单位为dBc.
• 互调抑制比(IMR)为70dBc。

2x2杂散特性电平可以从下式中得到：

IIP2 = 2 × IMR + PSPUR = IMR + PRF
IIP2 = 2 × 70dBc + (-75dBm) = 70dBc + (-5dBm)
IIP2 = +65dBm

IIP2 = 2 × IMR + PSPUR = IMR + PRF
IIP2 = 2 × 65dBc + (-70dBm) = 65dBc + (-5dBm)
IIP2 = +60dBm

### UMTS WCDMA举例

IIP2Cascade = IIP2Mixer – 增益 + 2 × 灵敏度 = +128dBm
IIP2Cascade = 65 – (-2 +25 –2) + 2 × (30 +12) = +128dBm

### 参考文献

1. CDMA Mobile Radio Designby John B. Groe, Lawrence E. Larson, published by Artech House Publishers, 2000.
2. RF and Microwave Circuit Design for Wireless Communications, by Lawrence E. Larson, published by Artech House Publishers, 1997.
3. RF Design Guide Systems, Circuits, and Equations by Peter Vizmuller, published by Artech House, 1995.
4. Understanding and Enhancing Sensitivity in Receivers for Wireless Applications, Technical Brief SWRA030, Texas Instruments, Edited by Matt Loy, May 1999.
5. 3G TS 25.141, 3rd Generation Partnership Project; Technical Specification Group Radio Access Networks; Base station conformance testing (FDD), Release 1999.

### 注

1. 输出交调点是将系统或者电路测量时所得到的输入交调点加上增益(以dB为单位)后得到。

### 参考电路

1. CDMA Mobile Radio Designby John B. Groe, Lawrence E. Larson, published by Artech House Publishers, 2000.
2. RF and Microwave Circuit Design for Wireless Communications, by Lawrence E. Larson, published by Artech House Publishers, 1997.
3. RF Design Guide Systems, Circuits, and Equations by Peter Vizmuller, published by Artech House, 1995.
4. Understanding and Enhancing Sensitivity in Receivers for Wireless Applications, Technical Brief SWRA030, Texas Instruments, Edited by Matt Loy, May 1999.
5. 3G TS 25.141, 3rd Generation Partnership Project; Technical Specification Group Radio Access Networks; Base station conformance testing (FDD), Release 1999.

### Notes

1. The output intercept point is merely the input intercept point plus the gain (in dB) of the circuit or system under measurement.