DVB-S Half-NIM Tuner Reference Design Uses the MAX2120 Tuner

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. 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 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.