Tool/software:
I am doing testing on the frequency response, and things are not looking as flat as they should be according to the datasheet.
My samplerate is 744kHz, and I am using the linear-phase interpolation filters.
According to the datasheet, that would be -0.2dB @ 0.15xFS = 111kHz.
I am measuring around -0.6dB @ 90kHz.
Test methodology: DAC is being fed 16 bit I2S from DSP generating a sine wave.
Just wondering if there is something wrong with my expectations, testing methods, or settings used to initialize the DAC (included below).
// SW reset
data = 0x00;
i2c_write_reg(kDacBus, kDacAddress, 0x00, &data, 1);
data = 0x01;
i2c_write_reg(kDacBus, kDacAddress, 0x01, &data, 1);
std::this_thread::sleep_for(std::chrono::milliseconds(2));
data = 0x00;
i2c_write_reg(kDacBus, kDacAddress, 0x00, &data, 1);
// Bring out of sleep mode
data = 0x09;
i2c_write_reg(kDacBus, kDacAddress, 0x02, &data, 1);
std::this_thread::sleep_for(std::chrono::milliseconds(2));
// Disable GPIO1
data = 0;
i2c_write_reg(kDacBus, kDacAddress, 0x0a, &data, 1);
// Primary ASI: I2S, 16 bit data
data = 0x40;
i2c_write_reg(kDacBus, kDacAddress, 0x1a, &data, 1);
// Primary ASI RX Channel 2: I2S right slot 0
data = 0x30;
i2c_write_reg(kDacBus, kDacAddress, 0x29, &data, 1);
// DAC demod rate override
data = (1 << 4);
i2c_write_reg(kDacBus, kDacAddress, 0x4f, &data, 1);
// DAC: wide bandwidth
data = 0xe1;
i2c_write_reg(kDacBus, kDacAddress, 0x65, &data, 1); // Channel 1p
i2c_write_reg(kDacBus, kDacAddress, 0x6c, &data, 1); // Channel 2p
data = 0xe0;
i2c_write_reg(kDacBus, kDacAddress, 0x66, &data, 1); // Channel 1m
i2c_write_reg(kDacBus, kDacAddress, 0x6d, &data, 1); // Channel 2m
// Disable DAC biquads
data = (1 << 4);
i2c_write_reg(kDacBus, kDacAddress, 0x73, &data, 1);
// Disable inputs, enable outputs
data = 0x0c;
i2c_write_reg(kDacBus, kDacAddress, 0x76, &data, 1);
// Power up DAC
data = 0x40;
i2c_write_reg(kDacBus, kDacAddress, 0x78, &data, 1);
