图1. MAX2120调谐器的DVB-S Half-NIM参考设计。

重要设计特性：

• 采用中国DVB-S市场通用的外壳结构；无需修改即可使用
• 采用分离的LNA有源环通
• LNB 12V馈电

图2. 系统框图

实验室测试

电源电流

Parameter	Conditions	Measured	Units
Supply Current	LNA supply 3.3V, Ta = +25°C	26	mA
	LNA + MAX2120 3.3V, Ta = +25°C	115	mA

 

主信号通道性能
测试条件包括：V_CC =　+3.3V，RF输入信号规格如下表所示；采用默认寄存器设置；T_a = +25°C。

Parameter	Test Conditions	Frequency	Measured	Target	Units
RF Input Frequency		950 to 2150	—	—	MHz
Input Return Loss (75Ω system)	Measure at input port	—	< -6	< -6	dB
Overall Voltage Gain	Unbalanced source impedance = 75Ω, GC1 = 0.5V and GC2 = +15dB	1050MHz	91	> 80	dB
		1550MHz	88
		2150MHz	83
Noise Figure	GC2 = +10dB, GC1 = 0.5V	1050MHz	5.5	< 7	dB
		1650MHz	5.54
		2150MHz	7.45
I/Q Amplitude Error	Measured at 2MHz; filter bandwidth set to 22MHz	—	0.25	< ±1	dB
I/Q Quadrature Phase Error	Measured at 2MHz; filter bandwidth set to 22MHz	—	< 2.5	< 3.5	Deg
IIP3 (In Band)	GC1 set to provide the nominal baseband output drive when mixing down a -23dBm tone at 2055MHz to 5MHz baseband (fLO = 2050MHz). GC2 set for 7dB gain. Two tones at -26dBm each are applied at 2056MHz and 2060MHz. The IM3 tone at 2MHz is measured at baseband.	—	-1.5	-2	dBm
IIP3 (Out of Band)	GC1 set to provide the nominal baseband output drive when mixing down a -23dBm tone at 2055MHz to 5MHz baseband (fLO = 2050MHz). GC2 set for 7dB gain. Two tones at -20dBm each are applied at fLO -100MHz and fLO -195MHz. The IM3 tone at 5MHz is measured at baseband.	—	10	5	dBm
IIP2 (Broadband)	GC1 set to provide the nominal baseband output drive when mixing down a -23dBm tone at 2175MHz to 5MHz baseband (fLO = 2170MHz). GC2 set for 7dB gain. Two tones at -20dBm each are applied at 925MHz and 1250MHz. The IM2 tone at 5MHz is measured at baseband.	—	12.5	14	dBm
Phase Noise	1kHz offset, fLO =1000MHz	—	-73.3	-70	dBc/Hz
	10kHz offset, fLO = 1000MHz		-85.6	-82
	100kHz offset, fLO = 1000MHz		-108.1	-102
	1MHz offset, fLO = 1000MHz		-120.8	-122
Local Oscillator Signal Leakage at RF Input Terminal	Measured at RF input port with 50MHz increment step from 925MHz to 2175MHz	—	< -80	< -63	dBm

 

环通性能

Parameter	Conditions	Measured	Target	Units
Frequency Range	925MHz to 2175MHz	—	—	MHz
Return Loss at TV_OUT	Antenna input terminated with 75Ω	< -6	< -6	dB
Power Gain at TV_OUT	—	-0.4 to 2.8	-1 to 3	dB
Noise Figure at TV_OUT	—	< 5.5	< 6	dB
TV_OUT to ANT_IN Isolation	—	35.1	35	dB

 

系统性能

将MAX2120 Half-NIM调谐器连接到DVB-S解调器进行DVB-S系统性能测试。

图3. 全频段内不加噪声情况下，DVB-S在4.42Msps码率下，系统灵敏度优于-92.5dBm；在27.5Msps码率下，灵敏度优于-84dBm。

图4. 全频段内加噪声情况下，DVB-S在4.42Msps码率下，系统灵敏度优于-85dBm；在27.5Msps码率下，灵敏度优于-77.5dBm。此时，AWGN噪声C/N = 5dB。对4.42Msps的数据速率，噪声带宽为5.7MHz；对于27.5Msps的数据速率，噪声带宽为35.2MHz。

详细说明

MAX2120参考设计为卫星STB提供了一个紧凑的Half-NIM DVB-S调谐器方案，该设计覆盖925MHz到2175MHz整个RF范围。MAX2120为完全集成的硅调谐器，内部包括LNA、RF和IF VGA、混频器以及一个可变带宽的基带LPF。该调谐器采用单电源3.3V供电，外部仅需要少量的无源元件即可组成一个完整的DVB-S RF前端方案。