Output Noise of AD5541A and AD5542A


I'm a DFAE in Japan. Our customer asks a question about AD5541A and AD5542A. Comparing the output noise spec between AD5541A and AD5542A, AD5542A is better than AD5541A. Since AD5542A has RFB and RINV, I thought that the noise would be worse because it was affected by those Johnson noises. But in reality it was the opposite. Could you please tell me the reason?