Slide 1 Slide 2 Slide 3 Slide 4 Slide 5 Slide 6 Slide 7 Slide 8 Slide 9 Slide 10 Slide 11 Slide 12 Slide 13 Slide 14 Slide 15 Slide 16 Slide 17 Slide 18 Slide 19 Slide 20 Product List
High Speed Amplifiers for Video Applications Part 2 Slide 7

Here is a circuit arrangement which provides an overall gain of +2, is DC coupled, and delivers "zero-volt-in" -"zero-volt-out" when using a non-rail-to-rail output device such as the LMH6723. In order to accommodate the input common mode voltage range or CMVR of the LMH6723, the network consisting of R1, R2, and R4 is used. This network shifts the zero volt to .7 volt video signal to a voltage within the CMVR of the LMH6723. As a consequence of this action, the video input goes through a signal amplitude loss of about 60% in this case. This loss can be made up for by the action of the LMH6723 Op Amp and proper selection of other gain setting components, R6 through R8. The voltage shift in this case is set so that the lowest voltage on the Op Amp plus input would be at three volts which is well within the device’s input CMVR as we had already explained in the earlier foil. To achieve an overall gain of +2, R8 in conjunction with the parallel combination of R7 and R6 should amount to a gain of +4 for an overall non-inverting gain of +5. As mentioned earlier, this gain of five along with the gain of .4 volts per volt from input to the positive input of the Op Amp yields an overall gain of +2. If you recall from the previous foil, the optimum resistance for the LMH6723 at the gain of +5 is given in that graph to be RF = 470 ohms. That’s why R8 here is shown at that value, 470.

PTM Published on: 2011-11-21