Hello!
We have some questions when using vca2615rgzt. I hope you can give me some help and answers.
Problem: we use vca2615 as part of automatic gain control. Under the condition of almost the same input and output, the maximum difference of VCNTL control voltage of different vca2615 is 0.2V. According to the corresponding curve relationship (as shown in Figure 1), the VCNTL difference of 0.2V means that there is a difference of 5dB magnification. However, the gain error in the chip manual is - 1.5dB and + 1.5dB (as shown in Figure 2).
I would like to know if the 5dB difference in gain between vca2615 devices is normal.
The schematic diagram of our vca2615 part is shown in Figure 3.
Main configuration of vca2615:
LNP Gain(G1,G2)=11;
FB(1-4)=1111;
Vcainsel - used to time-sharing switch the signals of ChannelA and ChannelB to VCAoutA and complete sampling.
Relevant tests we conducted:
Input signal: 3.7mhz sine wave (input from a and B in Fig. 3)
Amplitude: less than 1mV (stable)。
We use an oscilloscope to measure its waveform, through FFT test to the corresponding waveform amplitude corresponding DB value. DB value of signal at each test point. Through their differences, it is found that the VGA part of the chip is the main error source. I'm not sure the VGA part of this error is reasonable.
Table 1 is the data of our test quantity (converted to DB value through FFT function of oscilloscope)
The related schematic diagram and test data are in the attachment word.(I can't upload my schematic and data in this frame)
thank you!VCA2615 chip control gain difference exceeds specification limit.doc