what adc to use for digital am receiver

What are you trying to digitize? Digitized tuner or digitized output? They drives different requirements.

HI Linnix,

My radio would consist of a antenna and then a Low pass filter (analog) to select only the AM band. After this lowpass filter I want to use a a/d converter so that I can carry out the rest of demodulation( like downconversion etc) digitally.

Thanks.

Peak voltage from the antenna will vary from a few tens of microvolts to volts depending on your antenna and how close you are to the nearest AM transmitter.

My guess is that with a 10 bit ADC it would be normal to not have enough bits to demodulate weak stations with the input gain at a level where strong local stations are not clipping.

Bob

That's why you need the tuner to block the strong stations and AGC (Automatic Gain Control) to normalize the tunned signal.

10 bits should be fine for voice. Don't expect HiFi, digital or not.

You are not getting OP's goal, it is to digitize and simultaneously demodulate all channels at once. 12 bit 20 MSPS ADC is minimum for the task, more bits means better channel seperation and S/N for any channel.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller

If you are not too close to a local station, and if your local stations don't run a lot of power, you should be OK with about 0dBm full scale. If you have one station that is very strong (e.g., 5kW a kilometer away) I would recommend a passive notch filter to attenuate it. If you set full scale at about 0dBm, you should do fine if your ADC has a noise level of about -120dBfs/Hz. You'll want an ADC with low intermodulation distortion and good linearity to low levels. You only need a sample rate a little over twice the highest frequency of interest, but beware of the alias protection requirements. We generally use about 11th order elliptical filters. Nice thing is that the AM broadcast signals are generally pretty strong, so unless there are local hams or other users of the HF band, the potential alias signals shouldn't be terribly strong compared with the AM broadcast stuff. But because local conditions can vary drastically from place to place and even time to time, be prepared to either characterize your spectrum beforehand, or adjust things after you build the receiver. The actual number of bits in the ADC is less relevant than you might think, provided it has low enough noise and good enough linearity and distortion performance. Also, you can trade off sample rate for number of bits, to some extent: decimating a faster sample rate will get you more bits (slowly).

If it were my project, I'd look to digitize at 5Ms/s; the antialias filter would cut off above 2MHz and would be at least 100dB down at

3MHz and above. (11th order elliptical should get you close to 120dB if you're careful in its construction and use good coils.) I think there are a few good ADCs that will do 5Ms/s and 16 bits...but since I generally work at much higher sample rates, I'm not sure what the current state of 5Ms/s parts is.

Cheers, Tom