Original question:
Hi, I'm using VCA822 with cascade structure. Therefore, I could not give the right results of the simulations. With this structure below,
After U1, Instead of 1V, I get 724.8 mV as seen below.
After U2, I must get 2V if input 1V because I set the gain voltage as -0.6V (2V/V gain). Or for 724.8 mV, at least I must get approximately 1.5V. But I get 1.076V as seen below.
Why this results are so wrong? Am I making a mistake? Could you help me?
Hi Betul,
The behavior you are seeing is a result of the value of Rg and Rf you selected. As section 7.6 Figures 1 and 2 show, the differential input voltage and maximum gain adjust range are dependent on the values of Rg and Rf.
On the first stage, if decrease the input voltage you will see that you will reach the expected gain. If the required input voltage is 20mV, you can change Rg to 100 ohms and Rf to 5 kohms.
I have also attached a simulation of the cascaded VCA822 configuration you can use to simulate the behavior.
Thanks,
Nick
