CLC730036

8-Pin Dual Op Amp Eval. Boards N Part Numbers CLC730038, CLC730036 September 1997 1. Cut the input trace as shown in Figure 2 2. Use 25Ω for Rin 3. Terminate Rg at the input trace instead of ground (See Figure 2) 4. Add Rt for desired input impedance (input impedance = Rg||Rt) CLC730038 - DIP packages Uses all through-hole components CLC730036 - SOIC packages Uses all surface-mount components ■ Cut Here Both boards have identical circuit configurations and are designed for non-inverting gains. Inverting gains or other circuit configurations can be obtained with slight modifications to the boards. Use the evaluation boards as a: RF1 ■ Basic Operation Figure 1 shows the non-inverting schematic for both boards. The input signal is brought into the board through SMA connectors to the non-inverting input of the amplifier. The resistor Rin is used to set the input termination resistance to the op amp. The noninverting gain is set by the following equation: 25Ω RIN1 RG1 Rt Guide for high frequency layout Tool to aid in device testing and characterization ■ 830037 C VER Comlinear (970) 226-0500 ■ IN1 Figure 2: Modifications for Inverting Gains (CLC730038 board shown) Figure 3 illustrates the inverting schematic for both boards. +VCC C3 R Non-inverting Gain: 1 + f Rg 5 + 25Ω Rin2 The value of the feedback resistor, Rf, has a strong influence on AC performance. Refer to the product data sheet for feedback resistor selection. The output of the op amp travels through a series resistance, Rout, and then leaves the board through an SMA connector. The series resistance, Rout, matches transmission lines or isolates the output from capacitive loads. Dual Wideband Op Amp Evaluation Board The CLC730038 and CLC730036 evaluation boards are designed to aid in the characterization of Comlinear’s 8-pin, dual monolithic amplifiers. 3 25Ω Rin1 + C1 8 1 Channel 1 IN1 2 Rg1 - OUT1 Rout1 4 + Channel 2 IN2 6 Rg2 - 7 OUT2 Rout2 Rf2 Rt2 Rf1 C2 Rt1 + Select Rt to yield desired input impedance = Rg||Rt C4 -VCC Figure 3: Inverting Gain Configurations +VCC C3 + IN1 Rin1 3 + C1 8 2 - IN2 Rout1 4 5 OUT1 1 Channel 1 Rin2 + Channel 2 6 Rf1 7 OUT2 Rout2 Rf2 C2 Rg1 Isolation and Channel Matching Performance For maximum isolation between channels, proper power supply decoupling is required. Always include the bypass capacitors C1, C2, C3, and C4. The use of good quality capacitors also helps to achieve better isolation performance. Rg2 + C4 -VCC Figure 1: Non-inverting Gain Configurations Inverting Gain Operation The evaluation boards can be modified to provide an inverting gain configuration. Complete these steps to modify the board: © 1997 National Semiconductor Corporation Printed in the U.S.A. The evaluation boards have also been designed to minimize channel-to-channel crosstalk. The input and output pins of the amplifier are sensitive to the coupling of parasitic capacitances caused by power or ground planes and traces. To reduce the influence of these parasitics, the ground plane has been removed around these sensitive nodes. In multilayer boards, remove both the ground and power traces and planes around the input and output pins. http://www.national.com Layout Considerations General layout and supply bypassing play major roles in high frequency performance. When designing your own board, use the evaluation board as a guide and follow these steps as a basis for high frequency layout: Test Box (terminated in 50Ω) 1. Use a ground plane. 2. Include 6.8µF tantalum and 0.1µF ceramic capacitors on both supplies. 3. Place the 6.8µF capacitors within 0.75 inches of the power pins. 4. Place the 0.1µF capacitors less than 0.1 inches from the power pins. 5. Remove the ground plane under and around the part, especially near the input and output pins to reduce parasitic capacitance. 6. Minimize all trace lengths to reduce series inductances. 7. Use individual flush-mount sockets, for prototyping. Low Impedance Resistor Probe Test Box and Evaluation Board Ground Figure 4: “Cable/Resistor” Probe Configuration This “cable/resistor” probe, shown in Figure 4, forms a voltage attenuator between the resistor and the 50Ω termination resistance of the test box. This method allows measurements to be performed directly on the output pin of the amplifier. When evaluating only one channel on the board, complete the following on the unused channel: Measurement Hints If 50Ω coax and 50Ω Rin/Rout resistors are used, many of the typical performance plots found in the product data sheets can be reproduced. 1. Included Rf and Rg as shown in Figure 1 2. Ground the input 3. Load the output with 50Ω to ground When SMA connectors and cables are not available to evaluate the amplifier, do not use normal oscilloscope probes. Use low impedance resistive divider probes of 100 to 500Ω. If a low impedance probe is not available, then a section of 50Ω coaxial cable and a low impedance resistor (10Ω to 50Ω) may be used. Follow these 3 steps to create a “cable/resistor” probe: Power Supplies Refer to the product data sheet for the recommended supply voltages. Component Values ■ Rf, Rg - Use the product data sheet to select values ■ Rin, Rout - 50Ω (Refer to Basic Operation section for details) ■ Rt - Optional resistor for inverting gain configurations (Refer Inverting Gain Operation section for details) ■ C3, C4 - 6.8µF tantalum capacitors ■ C1, C2 - 0.1µF ceramic capacitors 1. Connect one end of the coax’s center to a test measurement box terminated in 50Ω. 2. Connect the other end of the cable’s center conductor to the low impedance resistor. (The open side of the resistor is now a probe.) 3. Connect the ground shield of the cable to evaluation board ground and test box ground. http://www.national.com 50Ω Coaxial Cable 2 DIP – Top Side DIP – Bottom Side SOIC – Top Side SOIC – Bottom Side +Vcc + C3 ROUT2 + C4 -Vcc OUT1 OUT2 GND RG2 IN2 RF2 C1 C2 ROUT1 RF1 Comlinear (970) 226-0500 RIN2 630037 B VER RG1 RIN1 IN1 3 http://www.national.com Customer Design Applications Support National Semiconductor is committed to design excellence. For sales, literature and technical support, call the National Semiconductor Customer Response Group at 1-800-272-9959 or fax 1-800-737-7018. Life Support Policy National’s products are not authorized for use as critical components in life support devices or systems without the express written approval of the president of National Semiconductor Corporation. As used herein: 1. Life support devices or systems are devices or systems which, a) are intended for surgical implant into the body, or b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. N National Semiconductor Corporation National Semiconductor Europe National Semiconductor Hong Kong Ltd. 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