I am developing a hardware where I would like to use an SDR circuit (RTL2832). However on the first prototype the circuit does not work. It has a USB interface however when I connect it to PC the device is not recognized.
On Windows machine I got the following error:
Unknown USB Device (Device Descriptor Request Failed)
usb 1-1: device descriptor read/64, error -71
The RTL2832 circuit is pretty simple. It has some capacitors, eeprom, its own DCDC converter for 1.2V and a USB interface. The DP and DM lines are connected with 27R to the USB interface.
The circuit got the 5V from USB, 3.3V is made by an LDO from USB 5V. The 3.3V is present, 1.2V is produced by the chip, there are no shorts on the board, no high current consumption, no heating, electrically it should work.
The USB lines looks like this:
CH1: DP CH2: DM
Seems like the DM line is on 2.5V and there is a small ~100mVp-p signal on it.
Any idea what to debug? What can be the issue?