Abstract: This reference design is a commercial Half-NIM DVB-S tuner that uses Maxim's MAX2120 satellite tuner IC. The reference design connects to the motherboard through a 12-pin connector. The downconverted satellite signal from the LNB is supplied to an active, discrete loop-through, which splits the signal into two paths. One signal goes to the MAX2120 and the other provides an additional output from the STB.
Figure 1. DVB-S Half-NIM reference design features the MAX2120 tuner.
Important Design Features
A Popular Form Factor Often Used in the Chinese DVB-S Market; Can Be Adopted Without Physical Modifications
Active Loop-Through Using a Discrete LNA
LNB 12V Power Feed-Through
Figure 2. System block diagram.
Lab Measurements
Supply Current
Parameter
Conditions
Measured
Units
Supply Current
LNA supply 3.3V, Ta = +25°C
26
mA
LNA + MAX2120 3.3V, Ta = +25°C
115
mA
Main Signal Path Performance
Test conditions include VCC =+3.3V; RF input signals as specified in the following table; default register settings; and Ta = +25°C.
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
Loop-Through Performance
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
System Performance
DVB-S system measurements for the MAX2120 Half-NIM are made by connecting to a DVB-S demodulator.
Figure 3. The DVB-S sensitivity without noise is better than -92.5dBm for 4.42Msps, and better than -84dBm for 27.5Msps across the band.
Figure 4. When noise is added, the DVB-S sensitivity is better than -85dBm for 4.42Msps, and better than -77.5dBm for 27.5Msps across the band. For this case, AWGN noise is added with C/N = 5dB. For the 4.42Msps data rate, the noise bandwidth is 5.7MHz; for the 27.5Msps data rate, the noise bandwidth is 35.2MHz.
Detailed Description
This MAX2120 reference design is a compact Half-NIM DVB-S tuner for satellite STB applications. The design covers the RF range from 925MHz to 2175MHz. The MAX2120 is a fully integrated silicon tuner, which includes a LNA, RF and IF VGAs, a mixer, and a variable-bandwidth LPF in the baseband stage. The tuner is powered by a single 3.3V supply. A small number of passive components are needed to form a complete DVB-S RF front-end solution.
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