Dsp nominal signal level ?
I have read (don"t know if it is right) that the DSP's input is a line in with impedance is typically around 10KΩ.
Also the nominal signal level at DSP input must be around 1 volt peak to peak. So what is this ? if i give 0.1 volt the DSP will not work? if i give 2 volt what?
i send an jpg data of bandwidth 14Khz.My DSPtransmitter is TMS 3220 C6416 DSK and the receiver is TMS 3220 C6713 DSK
tHANs :)
*i have already posted this in DSP forum but nothing yet 2 days
the DSP data sheet is your friend. they may recommend a desired AC pk-pk range for an IF input
If u can not find that, then I would assume the input to the DSP is an Analog to Digital converter that can have inputs between 0V and VCC. VCC, for a dsp, might be 1.1V, 1.5V, 3.3V...depends on what power supply voltage that ADC is running off of.
hi biff44 many thanks for the help. i found the integrated that make the ADC and DAC . is is AIC23 CODEC
http://www.ti.com/lit/ds/symlink/tlv320aic23b.pdf
at page 2-2 i read that:" Line Input to ADC Input signal level (0 dB) 1 V RMS"
at 3.2.1 "The ADC full-scale range
is 1.0 VRMS at AVDD = 3.3 V. The full-scale range tracks linearly with analog supply voltage AVDD. To avoid distortions,
it is important not to exceed the full-scale range."
so to work with efficiency i must feed this DSP with MAXXX 1 V (rms).
if i feed it with 0.5 more BER comes ? what is the minimum?
Usually you must put OpAmp before ADC input. ADC just convert voltage to bits, 16bit adc gives 16bits. If your input is too small, you will not use full resolution, for example only 3bits of 16bits, and your input will be almost the same as noise (1-2bits of noise). If input is too big, you get saturated bit output, for sine wave in would be clamped on both top and bottom side, sometimes look like square wave. So what you do is: put OpAmp with some potentiometers and tune you system for best performance. Sometimes potentiometer-like functionality is built-in in ADC, so you can controll it digitally through ADC commands.
Final perfomance can be also degraded if used wrong capacitor filter (impact on signal phase).
Dear Terminator good morning. Ok i understand what you mean. As you can see to my image of receiver at the end i have an active filter with some gain. But this gain is not so large enough.It gives output 0.1 V p-p and not uniform to all frequencies of the Bandwidth (14Khz).
i will make an non-inverting op.amp with two resistor (potentiometer).it will be ok with this simple structure?
Final stage output on the picture is 10kHz, OpAmp should work perfectily. Potentiometer resistor will help to find optimal value for amplification, and can be replaced to SMD resistor in case of mass production. I am not sure about your input signal. You can try something like MC33077, but if ADC needs more voltage, there are some new operational amplifier ICs with good parameters, or you can put two OpAmp to get best result: first one without potentiometer high-quality weak signal amplifier, second one conventional OpAmp with amplification tuning via potentiometer.
yes the final stage output is 10khz is the "center " freq. in reality is a signal going from : 3 to 17 khZ=BW=14KHZ. i will not have a prob with the op.amp right?
i have used this op amp at 36kHz and 18kHz signals, very good results. OpAmp input directly from Schottky diode mixer with very weak signal.
Actually your signal 14kHz frequency is an audio frequency, i can't imagine opAmp that can't work at least up to 90kHz.
From what i learned recently: in specific applications, where very precise phase is required, filtering capacitors must be choosen carefully. But it seems it is not your case.
So you can pick almost any "audio" operational amplifier.
ok this is fine many thanks.
to make the max voltage transfer: i have 50 ohm output mixer so the input of the op.amp must be at least ten time larger right?the op.amp input is high enough about this.
so maybe i will use this simple configuration http://i1284.photobucket.com/albums/...ps9ea61790.png
Your system already has about 50 to 70dB voltage gain, that's enough for most of the applications. If you adding more gain by OPAMP, it may won't help you a lot, as signal is mixed with noise and also you will encount interference problems.
the signal level into the ADC is depends on the RF signal level input. I thinks it's normal for about 0.1V input, 10dB backoff from full scale. For some OFDM receiver, usually the receiver try to keep the signal level at -10dBFS due to high PAR of OFDM signal. But in your case, it's not a OFDM signal, it's most likely a AM signal. You can decode the signal correctly with higer signal level at ADC input.
hi!
at the time i give 0.1volt peak to peak so 35mv rms.
the codec need maximum 1 volt rms..so i need more gain from op.ampl.
is it more clear now?
I think for this DSP you can use simple practical approach: check out ADC waveform buffer, how it looks like.
1) If it is almost flat line without noise (few little spikes) AND when you touch ADC input with screwdriver you can see big spikes - certainly ADC input is too low, and you need an opAmp
2) If you can see noisy zig-zag waveform with weak presence of received sinusoids, then it is probably problem of your RF part and opAmp will not help.
Or my second favourite RF output checking method:
use earphones cable, weld it to RF part output and connect to notebook/PC microphone input. Then use recording software and listen what comes out from RF part. If you can hear huge noise - problem with RF part output. If it is difficult to hear anything on microphone input (almost silent) - signal is probably too low. Computers audio chip ADC must be very similar to TMS DSP. I think it uses OpAmp on microphone input, or some integrated OpAmp in audio codec IC.
This is cool solution. i will check in the next days :)
i found the coder datasheet.but i don't know what is the minimum voltage level i can offer to work effiently.......