Hi, I want to rebuild a amplifier that Amplifies a 2.8Vpp DC-50MHZ Signal. The Output should be 12dB (11,3Vpp) as in the technical Datasheet mentioned. So far so good, it works with the THS3491 (right on the edge, but it works in the simulation. Now I want to design the Attenuation on CH1 and CH2. It attenuate 33dB. Problem I have with this is, that the Attenuation build a Voltage Divider with a T/Pi Attenuator and the 50 Ohm&also the 50 Ohm Load. It changes my Output Voltage.. How can I make that the CH1&CH2 Path (for measuring internal and output Voltage) don't change my Voltage? I thought that I could use a Buffer, than the Input is high impedance. But I couldn't find any Buffer that works with 0.1dB flatness at 50MHz and also the Input would be 22.5Vpp on the one at CH1.. How would you tackle this? Datasheet of Reference Design I want to build: https://www.omicron-lab.com/products/vector-network-analysis/accessories/b-amp-12-amplifier Thanks
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-33dB.GIF
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I suspect the TO speaks mainly German. So my answer written in German further back, first the translation made by DeepL: I assume that the following happens in the B-Amp 12: The two attenuators are resistor dividers with 50 ohm output impedance. They don't need to be T or Pi dividers. However, the load and the change in output impedance must be compensated by making the series resistance and gain slightly larger. The circuit shows estimated values, an exact calculation is more complex. There is of course a feedback from the Att_Out to the VOut. The high attenuation is chosen so that it can be neglected. Otherwise another buffer would be necessary. ------------------------- Ich vermute, der TO spricht hauptsächlich Deutsch. Also meine in Deutsch geschriebene Antwort weiter hinten, zuerst die von DeepL erstellte Übersetzung. Ich nehme an, dass im B-Amp 12 folgendes passiert: Die beiden Abschwächer sind Widerstands-Teiler mit 50 Ohm Ausgangsimpedanz. Das brauchen keine T- oder Pi-Teiler zu sein. Allerdings muss die Belastung und die Änderung der Ausgangsimpedanz dadurch kompensiert werden, dass der Längswiderstand und die Verstärkung etwas größer werden. Die Schaltung zeigt Schätzwerte, eine genaue Berechnung ist aufwändiger. Es gibt natürlich eine Rückwirkung vom Att_Out auf den VOut. Die hohe Dämpfung ist gewählt, damit sie vernachlässigt werden kann. Andernfalls wäre ein weiterer Buffer erforderlich.
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