[EMAIL PROTECTED] wrote: > On Thu, 21 Jun 2007, Matt Ettus wrote: > >> >>> >>> If there is no dc-removing capacitor in the circuitry , then should I >>> not expect that for a board using a single (positive) supply, that the >>> signal is always above zero? >>> >> >> >> No, you can put a negative voltage in, as long as it doesn't go below >> -3.33V. You need to look at the schematics -- the 8132 is a >> differential opamp with a common mode output set at 3.3V/2. >> > I meant that if you operate single supply, a negative input would be > mapped to a voltage referenced to the common mode output, not to zero. > So -.1 V would become 3.3/2 -.1 = 1.55 V. That's what the data sheet > seems to indicate if I read it correctly. Am I reading it correctly?
If you put 0V in, both outputs of the amp should be at 3.3/2. If you put in a positive voltage V, the + output should go up by V/2 and the negative output should go down by V/2. The reverse happens for negative voltages. >> Basically, the differential amps will clip if you go outside the range >> of -3.3V to +3.3V. You will also damage the differential amp if you go >> below -3.3V. >> >> The ADC will clip if you go outside the range -2V to +2V when set for >> minimum gain. >> >> >> Back to the subject of what your signal generator is doing, I don't >> know. If you measure the voltage on the sma connector with nothing >> connected, you will see that it is 0. If you connect a 1 V source >> through a 50 ohm resistor, you will see that there is 0.5V at the >> connector. If you connect -1 V through a 50 ohm resistor, you will see >> -0.5V at the connector. > > I do not. In fact, with no voltage applied to a powered up USRP, I > actually see +.109 V! So when I apply a -.1 (through a 50 ohm > resistor) I see just above zero. > > I see the behavior you describe only if I unpower the USRP/LF-RX. > What gives? Sounds broken. The LFRX has 2 inputs. Does the other one behave the same way? Matt _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
