Application Note Using the ARA05050 Amplifier Sections as Independent General-Purpose Gain Stages Rev 3 RELEVANT PRODUCTS • ARA05050 INTRODUCTION The ARA05050 CATV Reverse Path IC incorporates a Gallium Arsenide die consisting of three sections: (A) Amplifier #1; (B) Attenuator; (C) Amplifier #2. This Application Note describes how to operate these two amplifier sections as independent, stand-alone gain stages. The IC is designed as an integrated up-stream amplifier/attenuator/amplifier for use in first-generation DOCSIS-compatible CATV systems operating in the range of 5MHz to 85MHz. The three sections operate in unison to enable compliance with the relevant DOCSIS specifications that define reversepath gain-control and adjustment. However, the IC is ideal for any application that requires a generalpurpose low-frequency amplifier stage possessing excellent linearity characteristics. Both amplifier stages are identical. They can be operated together in cascade or operated independently with separate power supplies and biasing. The schematic diagrams in Figures 1 and 2 depict the configuration to be used for independent operation of each amplifier. The attenuator stage is disabled in each example. +5V 22uH RF IN 620 0.8pF ½ ARA05050 0.1uF 10 0.1uF 0.1uF 5.1K 20 5.1K 1uF 1.8K 1uF 4 5 11 * 3.3K 1uF RF OUT * 0.0 or 3.9ohms Figure 1: Single-Stage Amp (#1) Configuration Note: Amp Stage #2 and Attenuator Stage disabled. 02/2010 ARA05050 for Low Frequency Amplifier Applications +5V 22uH RF IN ½ ARA05050 620 RF OUT 24 0.1uF 0.1uF 20 5.1K 5.1K 1uF 1.8K 1uF 18 19 0.1uF 25 1uF * 3.3K * 0.0 or 3.9ohms Figure 2: Single-Stage Amp (#2) Configuration Note: Amp Stage #1 and Attenuator Stage disabled. CURRENT CONTROL The current drawn by each amplifier is controlled by adjusting the value of the resistor, Rs, that is placed at pin 11 for Amplifier #1 and at pin 25 for Amplifier #2. Electrical performance is characterized for Rs values of 0-ohms and 3.9-ohms. TYPICAL PERFORMANCE Each amplifier, when operated in accordance with the schematic diagrams shown above, yields a typical Gain, Noise Figure, and Harmonic Linearity performance profile as outlined in the tables below. Table 1: Gain vs. Frequency vs. Rs FREQUENCY 2 Gain(dB) (MHz) Rs = 0 ohms Rs = 3.9 ohms 10 16.32 16.14 20 16.19 16.02 30 16.15 15.99 40 16.08 15.94 50 16.06 15.91 75 15.73 15.60 100 15.42 15.30 125 14.96 14.86 150 14.46 14.45 175 14.15 14.07 200 13.76 13.68 225 13.32 13.25 250 12.88 12.83 Application Note - Rev 3 02/2010 ARA05050 for Low Frequency Amplifier Applications Table 2: Gain vs. Frequency vs. Rs FREQUENCY Gain(dB) (MHz) Rs = 0 ohms Rs = 3.9 ohms 10 16.32 16.14 20 16.19 16.02 30 16.15 15.99 40 16.08 15.94 50 16.06 15.91 75 15.73 15.60 100 15.42 15.30 125 14.96 14.86 150 14.46 14.45 175 14.15 14.07 200 13.76 13.68 225 13.32 13.25 250 12.88 12.83 Table 3: Harmonics vs Frequency (Pout = +58dBmV) FREQUENCY (MHz) Linearity - Harmonics (dBc) Rs = 0 ohms I = 104mA Rs = 3.9 ohms I = 77mA X2 X3 X2 X3 5 -58.4 -66.0 -49.3 -63.0 10 -59.5 -67.0 -49.7 -63.0 12 -60.0 -70.3 -50.3 -69.3 20 -58.8 -69.7 -49.3 -62.0 35 -59.0 -67.3 -52.3 -63.8 Application Note - Rev 3 02/2010 3 ARA05050 for Low Frequency Amplifier Applications S-parameters The input return-loss (S11), forward gain (S21), reverse isolation (S12), and output return-loss (S22) are plotted in the following four graphs presented below. Figure 3: Input Return Loss (S11) Amplifier Stage 1 or 2 Rs=3.9ohm Rs=0.0ohm -5 -10 S11 (dB) -15 -20 -25 -30 0 25 50 75 100 125 Frequency (MHz) 150 175 200 225 250 Figure 4: Gain (dB) (S21) Amplifier Stage 1 or 2 Rs=0.0ohm Rs=3.9ohm 17.0 16.5 16.0 S21 (dB) 15.5 15.0 14.5 14.0 13.5 13.0 0 4 25 50 75 100 125 150 Frequency (MHz) Application Note - Rev 3 02/2010 175 200 225 250 ARA05050 for Low Frequency Amplifier Applications Figure 5: Reverse Isolation (S12) Amplifier Stage 1 or 2 -15 Rs=0.0ohm Rs=3.9ohm -16 -17 -18 S12 (dB) -19 -20 -21 -22 -23 -24 -25 0 25 50 75 100 125 Frequency (MHz) 150 175 200 225 250 Figure 6: Output Return Loss (S22) Amplifier Stage 1 or 2 -5 Rs=0.0ohm Rs=3.9ohm -10 S22 (dB) -15 -20 -25 -30 0 25 50 75 100 125 Frequency (MHz) 150 Application Note - Rev 3 02/2010 175 200 225 250 5 ARA05050 for Low Frequency Amplifier Applications Linearity Plots of the third order output intercept (OIP3) point and the gain compression (P1dB) point as a function of Rs are depicted below. The testing conditions are published in the ARA05050 Data Sheet. Figure 7: OIP3 & P1dB vs Frequency Rs=3.9ohm Rs=0.0ohm 91 69.5 90 69.0 P1dB 89 0.0 3.9 OIP3 (dBmV) 88 87 68.0 67.0 3.9 85 68.5 67.5 0.0 86 66.5 OIP3 84 66.0 83 65.5 82 0 25 50 75 100 125 150 Frequency (MHz) COMPONENT PLACEMENT For best performance, it is suggested that the components be oriented nominally as shown in diagrams 1 & 2 below. Each component is dimensioned as “0603” with the exception of the 22uH inductor. Standard, low-cost double-sided pcb construction utilizing FR4 dielectric is adequate for use with this IC. It is recommended to fabricate the bottom layer as a solid ground plane devoid of DC and signal paths. The one exception that is permissible is the cross-over that can be seen immediately adjacent to the 22uH inductor element. 6 70.0 P1dB (dBmV) 92 175 200 225 65.0 250 The general orientation of the components is based upon the layout of the ARA05050 Evaluation Test Fixture. The original pcb file defining the Test Fixture artwork is available from ANADIGICS upon request. The pcb layout is designed to enable the operation of both stages simultaneously along with the Attenuator section. However, the user is encouraged to import this pcb file and to modify it in accordance with the particular needs of his system architecture. Application Note - Rev 3 02/2010 ARA05050 for Low Frequency Amplifier Applications RF OUT +5V 22uH 3.3k 4 5 1.8k 1uF 0.8pF 620 RF IN 20 0.1uF 10 0.1uF 11 (2) 1uF 5.1k 5.1k 1uF = GND VIA Figure 8: Single-Stage Amp #1 Components Notes: 1. Amp Stage #2 and Attenuator Stage disabled. (2) 0.0 or 3.9 Ohms. = GND VIA 5.1k 1uF 5.1k 1uF (2) 25 IN 0.1uF 24 0.1uF 20 620 1uF RF 1.8k 19 18 3.3k 22uH RF OUT +5V Figure 9: Single-Stage Amp #2 Components Notes: 1. Amp Stage #1 and Attenuator Stage disabled. (2) 0.0 or 3.9 Ohms. Application Note - Rev 3 02/2010 7 ARA05050 for Low Frequency Amplifier Applications PCB LAYOUT Thermal management and RF parasitics must be considered during the pcb layout process. Thermal Considerations The ARA05050 dissipates a maximum total power of 1.3Watts when both amplifier stages are biased using values for Rs of 0-ohms. Maximum MTF is achieved by minimizing the temperature of the active devices in the circuit die. A heat slug is incorporated into the bottom of the IC package to provide a low-resistance path for efficient thermal energy evacuation. Adequate heat sinking must be applied to the heat slug for optimal thermal management. A metalized pad with via holes to ground as shown in Figure 3 is recommended. The heat slug is soldered to this pad during the assembly process. It is also recommended that the solder mask outline depicted in Figure 4 be adopted for ease of solderability. RF Layout Considerations The ARA05050 is designed to drive a 75-ohm single-ended load. The layout of the PCB affects performance at RF frequencies. 8 The quality of the ground connections is a critical item in an RF layout. These ground connections must be low-impedance and be as short as possible. Specify 0.030-inch diameter via-holes to ground and locate them as close to the ground pins as possible. Other non-ground related aspects must be considered. For example, traces connecting IC pins to their respective components should have a low value of impedance. A few additional special considerations are listed below: Pins 5 & 19: The 1uF capacitor and the 20ohm chip resistor should be as close as possible to the IC pins. Pins 11 & 25: The 1uF bypass capacitor should be close to the pin. All bypass capacitors on the Vdd lines should be located as close as possible to the 22uH inductors. Application Note - Rev 3 02/2010 ARA05050 for Low Frequency Amplifier Applications 0.025 BSC 0.089 0.014 TYP BODY OUTLINE (NOMINAL) 0.025 MIN. 0.163 0.099 0.070 0.197 0.152 REF. 0.150 (12X)0.020 TO 0.060 DIA.P PLATED THRU HOLES. 0.060 TYP. 0.386 REF. 0.400 *Dimensions are in inches [Millimeters] Figure 10: PC Board Layout for Heatsink 0.016 TYP. 0.091 0.0535 0.025 TYP. 0.163 0.242 0.085 0.098 0.025 BSC 0.145 *Dimensions are in inches [Millimeters] Figure 11: Solder Mask Outline Application Note - Rev 3 02/2010 9 ARA05050 for Low Frequency Amplifier Applications ANADIGICS 141 Mount Bethel Road Warren, New Jersey 07059, U.S.A. Tel: +1 (908) 668-5000 Fax: +1 (908) 668-5132 URL: http://www.anadigics.com IMPORTANT NOTICE ANADIGICS, Inc. reserves the right to make changes to its products or to discontinue any product at any time without notice. The product specifications contained in Advanced Product Information sheets and Preliminary Data Sheets are subject to change prior to a product’s formal introduction. Information in Data Sheets have been carefully checked and are assumed to be reliable; however, ANADIGICS assumes no responsibilities for inaccuracies. ANADIGICS strongly urges customers to verify that the information they are using is current before placing orders. warning ANADIGICS products are not intended for use in life support appliances, devices or systems. Use of an ANADIGICS product in any such application without written consent is prohibited. 10 Application Note - Rev 3 02/2010