kgl_13gr
Member level 5
Hello! This is my first post to this forum so nice to meet you. Well the fact goes like that:
For a project at university we are required to connect an ADC and DAC in order to create a circuit that will be able to sample the input and reproduce the input waveform in the DACs output. We chose to use ADC0805 and DAC0808 from National Semiconductors. We constructed the circuit and it works fine for DC inputs.
We set up the ADC to do continuous conversions with a clock frequency of 640kHz. The reference voltage is 5.12 V and the analog input can be up to 5V positive. We use as an input a fully-rectified sinus. Now i have two problems-questions:
1)The A/D can sample with a frequency of at leaste 6.5 MHz. The D/A has a worst-case settling time of 1.2 μS(833 kHz). That means that a signal with frequency under 400 kHz should be sampled perfectly! We can get a pretty good signal in the DAC output only for frequencies below 300Hz!!!
2)(and most improtant) When we increase the amplitude of the sinus applied to the A/D input over 1 V it is chopped!! Any ideas why this could happen??
Thanks in advance for any ideas!
For a project at university we are required to connect an ADC and DAC in order to create a circuit that will be able to sample the input and reproduce the input waveform in the DACs output. We chose to use ADC0805 and DAC0808 from National Semiconductors. We constructed the circuit and it works fine for DC inputs.
We set up the ADC to do continuous conversions with a clock frequency of 640kHz. The reference voltage is 5.12 V and the analog input can be up to 5V positive. We use as an input a fully-rectified sinus. Now i have two problems-questions:
1)The A/D can sample with a frequency of at leaste 6.5 MHz. The D/A has a worst-case settling time of 1.2 μS(833 kHz). That means that a signal with frequency under 400 kHz should be sampled perfectly! We can get a pretty good signal in the DAC output only for frequencies below 300Hz!!!
2)(and most improtant) When we increase the amplitude of the sinus applied to the A/D input over 1 V it is chopped!! Any ideas why this could happen??
Thanks in advance for any ideas!