19-1493; Rev 0; 7/99 MAX2685 Evaluation Kit The MAX2685 evaluation kit (EV kit) simplifies testing of the MAX2685. This EV kit allows evaluation of the lownoise amplifier (LNA) as well as the downconverter mixer. Component List DESIGNATION QTY Features ♦ +2.7V to +5.5V Single-Supply Operation ♦ 50Ω SMA Inputs and Outputs ♦ Fully Assembled and Tested ♦ Allows Testing of All Device Functions DESCRIPTION C1, C3, C5, C17 4 0.1µF ceramic capacitors C2, C14, C15 0 Not installed C4, C8 2 47pF ceramic capacitors C6, C7, C10 2 330pF ceramic capacitors C9 1 3.3pF ceramic capacitor C11, C18 2 6pF ±0.1pF ceramic capacitors C12 1 1000pF ceramic capacitor C13 1 12pF ±0.1pF ceramic capacitor C16 1 10µF tantalum capacitor AVX TAJC106K016 L1 1 12nH inductor Toko LL1608-SH12NK L2 1 680nH ±5% inductor Coilcraft 1008CS-681XJBC 5% L3 1 820nH ±5% inductor Coilcraft 1008CS-821XJBC 5% L4 1 Not installed R1, R2 2 1kΩ resistors R3 1 75Ω resistor R4 1 15kΩ resistor R5 1 0Ω resistor R6, R7, R8 3 Not installed IFOUT+, IFOUT-, LNAIN, LNAOUT, LO, MIXIN 6 SMA connectors (PC edge mount) Ordering Information PART TEMP. RANGE MAX2685EVKIT -40°C to +85°C IC PACKAGE 16 QSOP _________________________Quick Start The MAX2685 EV kit is fully assembled and factory tested. Follow the instructions in the Connections and Setup section for proper device evaluation. Test Equipment Required This section lists the equipment recommended for verifying the MAX2685’s operation. It is intended as a guide only; some substitutions are possible. • Two RF signal generators capable of delivering at least 0dBm of output power at frequencies to 2GHz (HP 8648C or equivalent). One generator is required for the local oscillator (LO) source; the other is required for the mixer and LNA RF input. Only one generator is required to operate the LNA. • An RF spectrum analyzer that covers the MAX2685’s operating frequency range (the HP 8561E, for example). • A power supply that can provide up to 100mA at +2.7V to +5.5V. • An ammeter for measuring the supply current (optional). • Several 50Ω SMA cables. Connections and Setup JU1, JU2 2 3-pin headers GND, VCC 2 Eyelets U1 1 MAX2685EEE (16-pin QSOP) None 1 MAX2685 PC board This step-by-step guide explains how to get the EV kit operational and how to evaluate both the LNA and the downconverter mixer. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. Evaluates: MAX2685 General Description Evaluates: MAX2685 MAX2685 Evaluation Kit Low-Noise Amplifier (LNA) 1) Connect the SHDN jumper (JU2) on the EV kit to the “ON” position, SHDN = V CC . This enables the MAX2685. 2) Connect the GAIN jumper (JU1) on the EV kit to the “HI” position, GAIN = VCC. This places the LNA in high-gain mode. 3) Connect a 3V DC supply (through an ammeter, if desired) to the VCC and GND terminals on the EV kit. 4) Connect one RF signal generator to the LNAIN SMA connector. Do not turn on the generator’s output. Set the generator for an output frequency of 880MHz and a power level of -30dBm. 5) Connect a spectrum analyzer to the LNAOUT SMA connector on the EV kit. Set the spectrum analyzer to a center frequency of 880MHz, a total span of 200MHz, and a reference level of 0dBm. 6) Turn on the DC supply. The supply current should read approximately 8.5mA (if using an ammeter). 7) Activate the RF generator’s output. An 880MHz signal should show on the spectrum analyzer’s display and should indicate a typical gain of 15dB after accounting for cable losses. 8) Test the MAX2685’s low gain mode by changing the output power on the signal generator to -10dBm and setting the GAIN jumper (JU1) on the EV kit to the “LO” position, GAIN = GND. The supply current should read approximately 4mA (if using an ammeter). An 880MHz signal should show on the spectrum analyzer’s display and should indicate an attenuation of 12dB after accounting for cable losses. 9) If desired, test the shutdown feature by moving the SHDN jumper (JU1) into the “OFF” position. This disables the part and reduces supply current below 1.0µA. Downconverter Mixer 1) Connect the GAIN jumper (JU1) on the EV kit to the “HI” position, GAIN = VCC. This places the mixer in high-gain mode. 2) Remove the RF signal generator and spectrum analyzer from the LNAIN and LNAOUT connections. The DC supply connections needed for testing the mixer are the same as in the LNA section. 3) Connect one RF signal generator (with the output disabled) to the LO SMA connector. Set the frequency to 960MHz and the output power to -8dBm. 2 4) Connect the other RF signal generator (with the output disabled) to the MIXIN SMA connector. Set the frequency to 880MHz and the amplitude to -25dBm. 5) Connect the spectrum analyzer to the IFOUT+ SMA connector. Set the spectrum analyzer to an 80MHz center frequency, a 1MHz span, and a 0dBm reference level. 6) Turn on the LO and RF signal generators. 7) An 80MHz signal should show on the spectrum analyzer’s display and should indicate a typical gain of 6.1dB after accounting for cable losses. 8) If desired, connect the GAIN jumper (JU1) on the EV kit to the “LO” position, GAIN = GND. This places the mixer in low-gain mode. An 80MHz signal should appear on the spectrum analyzer’s display and should indicate a typical gain of 4.6dB after accounting for cable losses. Detailed Description The MAX2685 EV kit’s circuitry is described in this section. For more detailed information about the operation of the device itself, refer to the MAX2685 data sheet. Low-Noise Amplifier The LNA circuitry consists of matching networks and DC-blocking capacitors at the input and output. Downconverter Mixer RF Input The downconverter mixer’s RF input, MIXIN, requires a simple matching network. C10 provides DC blocking, and C9 is used to match the input to 50Ω at 880MHz. Downconverter Mixer LO Input The downconverter mixer’s LO input is terminated with a 75Ω resistor, R3, at the SMA input. C8 provides DC blocking. Downconverter Mixer Differential IF Output The mixer output can be evaluated in either a singleended or differential configuration. The MAX2685 EV kit is shipped with a differential to single-ended converter for single-ended testing. See the IF Output Configuration section. _______________________________________________________________________________________ MAX2685 Evaluation Kit Shutdown Jumper JU2 controls the IC’s operating modes. Enable the MAX2685 by connecting the SHDN pin to VCC. Do this by placing the shunt across pins 1 and 2 of jumper JU2. Shut down the MAX2685 by connecting the SHDN pin to GND. Do this by placing the shunt across pins 2 and 3 of jumper JU2. IF Output Configuration The EV board contains a circuit that converts the MAX2685 mixer’s differential output to a single-ended output. This is done with components L2, L3, C11, C13, C18, and R4. The resonant network composed of L2, C11, and C18 transforms the IFOUT- signal by 180° at IFOUT+. L3 is primarily a choke. The 50Ω match on the EV board was obtained by initially using a large value for C13 so it does not affect the impedance. Using a network analyzer calibrated between 70MHz and 90MHz, monitor S22 of the IF output. It is a high-resistance output that swings near the high-impedance end of the Smith chart. Adjust L2, C11, and C18 so that the network analyzer sweep crosses the 50Ω circle at the desired IF frequency, 80MHz. Choose the final value of the series capacitor, C13, to transform the impedance to the center of the Smith chart. This is a narrowband match. To reduce the Q of this match and make it more broadband, add R4. This is required to make the match manufacturable considering variations in component tolerance. In initially choosing the component values for the resonant network (L2, C11, and C18), note that increasing the value of L2 makes the match more broadband. If a higher impedance output is desired to interface with a filter, C13 may not be required and you may set the output impedance with R4. For a differential output, footprints for L4 and C15 are available on the EV board to establish a differential output on the board edge. In addition, footprints labeled as R5–R8 are available for other experimentation. PC Board Layout Good PC board layout is an essential aspect of RF circuit design. The EV kit’s PC board can serve as a guide for laying out a board using the MAX2685. Each VCC node on the PC board has its own decoupling capacitor. This minimizes supply coupling from one section of the MAX2685 to another. A star topology for the supply layout, in which each VCC node on the MAX2685 circuit has a separate connection to a central VCC node, can further minimize coupling between the LNA and mixer sections of the MAX2685. _______________________________________________________________________________________ 3 Evaluates: MAX2685 Gain Control and LNA Bypass Switch Jumper JU1 controls the LNA bypass switch and the overall gain of the MAX2685. Enable the LNA and switch the device to high-gain mode by placing the GAIN jumper (JU1) into the “HI” position, GAIN = VCC. Bypass the LNA and reduce the overall gain by placing the GAIN jumper (JU1) into the “LO” position, GAIN = GND. Evaluates: MAX2685 MAX2685 Evaluation Kit C1 0.1µF J1 L1 12nH C7 330pF LNAIN C2 OPEN 1 R1 1k VCC 1 2 2 C3 0.1µF 3 JU1 GAIN 3 4 5 VCC C4 47pF R2 1k GND 2 1 GND GND GAIN MIXIN VCC GND SHDN GND 6 7 C5 0.1µF 3 JU2 SHDN 8 J4 R3 75Ω LNAOUT GND IFOUT+ IFOUT- VCC C8 47pF 14 C10 330pF 13 J6 MIXIN C9 3.3pF 12 VCC C12 1000pF 11 L3 820nH C13 12pF 10 9 C11 6pF LO J5 MAX2685 15 VCC LNAIN LO VCC LNAOUT 16 L2 680nH R4 15k R5 0Ω IFOUT+ C18 6pF VCC L4 OPEN J8 C6 330pF IFOUT- J9 R7 OPEN VCC J10 C16 2 10µF C17 0.1µF Figure 1. MAX2685 EV Kit Schematic 4 R6 OPEN C14 OPEN C15 OPEN 1 J7 _______________________________________________________________________________________ R8 OPEN MAX2685 Evaluation Kit Evaluates: MAX2685 1.0" Figure 2. MAX2685 EV Kit Component Placement Guide— Component Side 1.0" 1.0" Figure 3. MAX2685 EV Kit Pad Placement Figure 4. MAX2685 EV Kit PC Board Layout—Component Side _______________________________________________________________________________________ 5 Evaluates: MAX2685 MAX2685 Evaluation Kit 1.0" 1.0" Figure 5. MAX2685 EV Kit PC Board Layout—Ground Plane Figure 6. MAX2685 EV Kit PC Board Layout—Solder Side Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 6 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.