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## VCA824IDG4 Datasheet(PDF) 25 Page - Texas Instruments

 Part No. VCA824IDG4 Description Ultra-Wideband, > 40-dB Gain Adjust Range, Linear in V/V Variable Gain Amplifier Download 41 Pages Scroll/Zoom 100% Maker TI1 [Texas Instruments] Homepage http://www.ti.com Logo

## VCA824IDG4 Datasheet(HTML) 25 Page - Texas Instruments

 25 / 41 page 9630-3-6-9-12-15-18-21-24Frequency(Hz)1M10M1G100MInitialFrequencyResponseoftheVCA824withRCLoadEqualizedFrequencyResponseRF+VINRG+RG--VINFBRS20WVIN1VCA824RGR1C1RSVIN2G=2 ´´RFRG1+sR CG11+sR C11VCA824www.ti.comSBOS394D – NOVEMBER 2007 – REVISED JANUARY 20169.1.2 Differential EqualizerIf the application requires frequency shaping (the transition from one gain to another), the VCA824 can be usedadvantageously because its architecture allows the application to isolate the input from the gain setting elements.Figure 70 shows an implementation of such a configuration. The transfer function is shown in Equation 5.(5)Figure 70. Differential EqualizerThis transfer function has one pole, P1 (located at RGC1), and one zero, Z1 (located at R1C1). When equalizing anRC load, RL and CL, compensate the pole added by the load located at RLCL with the zero Z1. Knowing RL, CL,and RG allows the user to select C1 as a first step and then calculate R1. Using RL = 75-Ω, CL = 100pF andwanting the VCA824 to operate at a gain of 2 V/V, which gives RF = RG = 453-kΩ, allows the user to selectC1 = 15.5 pF to ensure a positive value for the resistor R1. With all these values known, to achieve greater than300 MHz bandwidth, R1 can be calculated to be 20-Ω. Figure 71 shows the frequency response for both theinitial, unequalized frequency response and the resulting equalized frequency response.Figure 71. Differential Equalization of an RC Load9.1.3 Differential Cable EqualizerA differential cable equalizer can easily be implemented using the VCA824. An example of a cable equalizationfor 100 feet of Belden Cable 1694F is illustrated in Figure 73, with Figure 72 showing the result for thisimplementation. This implementation has a maximum error of 0.2 dB from DC to 70 MHz.Copyright © 2007–2016, Texas Instruments IncorporatedSubmit Documentation Feedback25Product Folder Links: VCA824