EL5108 Video Buffer Forms Differential Line Driver/Receiver ® October 19, 2004 Application Note The EL5108 Video Buffer can be used to implement differential line drivers and receivers with a minimum of external components (see Figure 2). Common mode rejection is set by the internal matched thin film resistors which are pin strapped to set the various closed loop gains that are required. AN9524.1 The oscilloscope photograph illustrates the common mode rejection of the receiver. VIN is a 10MHz, 1.5VP-P sine wave. The ground reference of U1 is driven by a 1MHz, 1.5VP-P common mode signal. The combined signal, seen on the top trace is measured at RX-. VOUT, on the bottom trace, is a faithful reproduction of VIN with the common mode signal removed. VIN is terminated into 75Ω and drives U1 and U2 amplifiers. U1 has a gain of -1 while U2 has a gain of +1. These amplifiers create a differential signal with a gain of 2. Series 75Ω resistors provide impedance matching to the transmission line. R X- The 150Ω termination resistor on the receive side of the transmission line provides proper impedance matching and attenuation for a gain of one at the receive input. U3 and U4 perform differential to single ended conversion and provide common mode rejection. VOUT U3 is configured in a gain of +2. U2B subtracts out common mode signals and applies a gain of +2 to differential signals. When VOUT is terminated into 75Ω, the overall gain from VIN to VOUT is unity. Because of the gain of +2 in U3, the peak voltage at the receiver may not exceed 1.5V. VIN = 10MHz, 1.5VP-P VCM = 1MHz, 1.5VP-P ON GROUND OF U1 WITH RESPECT TO U3 FIGURE 1. COMMON MODE REJECTION VIN 75Ω + - 100Ω + U1 75Ω - TX + - U3 RX 150Ω + + U2 + - + 75Ω U4 75Ω + VOUT - 75Ω FIGURE 2. DIFFERENTIAL VIDEO LINE DRIVER/RECEIVER 1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 321-724-7143 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 1995, 2004. All Rights Reserved All other trademarks mentioned are the property of their respective owners. Application Note 9524 All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see www.intersil.com 2