Maxim > Design Support > Technical Documents > Application Notes > Wireless and RF > APP 2243 Keywords: rf, rfic, wireless, lna, vga, if, step, attenuator, rf ics, radio frequency, rfics, low noise amplifier, amps APPLICATION NOTE 2243 MAX2371 Makes a Terrific IF AGC Amplifier at 220MHz By: Roger Bremer, Strategic Applications Engineer Sep 26, 2003 Abstract: The MAX2371 is an ideal low-noise amplifier (LNA) at low IF frequencies when a large dynamic range of gain is needed. This part works at frequencies not specified in the data sheet. Specific to this note is the 220MHz frequency. General Description The MAX2371 is a low-noise amplifier (LNA) IC designed for very low intermediate frequency receiver applications. The LNA features both a switched attenuator and an automatic gain control (AGC) intended as a low-noise gain stage. Between these two features, the device provides over 65dB of gain-control range. The LNA has a selectable current mode. When high current mode is selected, the IC will perform with maximum gain, IP3 and low noise figure. When peak performance is not required, low-current mode slightly degrades the aforementioned parameters while reducing current consumption. Click here for an overview of the wireless components used in a typical radio transceiver. Although the MAX2371 is specified in its data sheet as operating between 136 and 174 MHz, the part also functions well at other frequencies. The data in this note documents performance at 220MHz. The only change required to use the MAX2371 at this alternative frequency is to update the component values for the input and output matching networks. The values used are represented in the MAX2371 EVKit Schematic and BOM included at the end of this note. Test Setup Test Conditions: 1) Vcc = 2.85 V 2) Frequency = 220 MHz 3) Input Power = -30 dBm 4) Two Tone Spacing = 625 kHz 5) RF_ATTN = LOW 6) LNA_I = HIGH Test Setup Diagram: Page 1 of 6 Figure 1. Diagram of the LNA test setup used to evaluate the MAX2371. Measurement Results Parameter Measured Data Comment Max. Gain(dB) 12.5 Vgc = 1/2 Vcc Noise Figure(dB) 2.2 Vgc = 1/2 Vcc IIP3(dBm) 1.5 Vgc = 1/2 Vcc Dynamic Range(dB) 55.0 From VGC Gain Step (dB) 17.5 From RF_ATTN Icc over Gain(mA) 3.7 Gain, IIP3, P1dB IIP3, P1dB and Gain were measured for the MAX2371 over control voltage and temperature to show all operating conditions. Three temperatures were tested (-10°C, +25°C, +70°C) along with 8 AGC voltages. The results are plotted below. Page 2 of 6 Figure 2. The downward sloped curve set shows that Gain varies less than 0.3dB over temperature. Figure 3. IIP3 has a variance of approximately 3.5dB over temperature. Page 3 of 6 Figure 4. Input P1dB varies by less than 2dB over temperature. MAX2371 IF Amplifier Circuit S11 and Circuit S22 S11 and S22 were measured against control voltage. The results are plotted below. The input and output were each matched to 50 ohms using single section L-C matches. Figure 5. Variance of S11 and S22 over VGC range. Conclusion This study of the MAX2371 illustrates its effectiveness and viability as an LNA at 220MHz. The IC provides good noise figure and low current consumption while offering a wide gain range. MAX2371 EVKit Schematic Page 4 of 6 Figure 6. MAX2371 EVKit BOM Item Reference Description Value 1 C1 0402 Capacitor Open 2 C10 0402 Capacitor 0.015uF 3 C19 Capacitor 100nF 4 C2 0402 Capacitor 8.2pF 5 C3 0402 Capacitor Open 6 C4 0402 Capacitor 1500pF 7 C5 0402 Capacitor 1500pF 8 C6 0402 Capacitor 4.7pF 9 C7 0402 Capacitor Open 10 C8 0805 Capacitor 1.0uF 11 C9 Capacitor 10nF 12 J1-3 Three PIN INLINE HEADER 13 J4 SIX PIN INLINE HEADER 14 J5-6 Two PIN INLINE HEADER 15 L1 0603 Inductor 16 L2 17 L4 0603 Inductor 33nH 18 L5 Inductor 82nH Open 39nH Page 5 of 6 19 P1-2 SMA Connector 20 R1 1.1K 21 R2 220 22 R3 0 23 U1 MAX2371EGC LNA/AGC Attenuator Related Parts MAX2371 LNAs with Step Attenuator and VGA Free Samples More Information For Technical Support: http://www.maximintegrated.com/support For Samples: http://www.maximintegrated.com/samples Other Questions and Comments: http://www.maximintegrated.com/contact Application Note 2243: http://www.maximintegrated.com/an2243 APPLICATION NOTE 2243, AN2243, AN 2243, APP2243, Appnote2243, Appnote 2243 Copyright © by Maxim Integrated Products Additional Legal Notices: http://www.maximintegrated.com/legal Page 6 of 6