# Where to find specialty circuits

I have been looking through the internet and I can't find a place that provides specialty electonic circuits. The type I need is a digital filter with and op-amp. I was told they are available. Can someone plaese tell me where I can find this type of circuit.

berkeman
Mentor
Not sure exactly what you're looking for -- can you be more specific? You usually implement a digital filter in a CPLD or FPGA or ASIC or microcontroller (uC) or DSP engine like the TI TMS320 series.

Check out these manufacturer websites to see if you see something close:

Maxim http://www.maxim-ic.com/
Texas Instruments http://www.ti.com/
Linear Technology http://www.linear.com/

What I need is a circuit that includes a analog to digital converter, digital signal processor, digital to analog converter and an op-amp.
I really can't make the circuit myself, so I need a circuit that is premade to my specifications

mgb_phys
Homework Helper
If you need to do it yourself I would probably look at a DSP+FPGA dev kit from someone like altera.

berkeman
Mentor
What I need is a circuit that includes a analog to digital converter, digital signal processor, digital to analog converter and an op-amp.
I really can't make the circuit myself, so I need a circuit that is premade to my specifications
Sounds like you just need to find an evaluation board for your favorite uC that also has those other peripherals on it. That sounds like a pretty common configuration for eval boards. Which uC are you considering? What eval boards are available for those uCs?

I'm sorry but I don't understand what uC stands for. And do you know of any sites that would have a good selection of the certain type of eval board I'm looking for. I did search but couldn't find the particular circuit.

mgb_phys
Homework Helper
uC is microchip or microprocessor, the u should really be a $\mu$

Most simple uC (eg http://en.wikipedia.org/wiki/Atmel_AVR) have ADC and DACs, it depends how fast, how many bits and how complex a program you need

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berkeman
Mentor
I'm sorry but I don't understand what uC stands for. And do you know of any sites that would have a good selection of the certain type of eval board I'm looking for. I did search but couldn't find the particular circuit.
I defined uC for you in my post #2 above. uC = microcontroller, and uP = micoprocessor.

The difference is that a uC is a uP that also has some IO capability.

So I was reading up about eval boards. And I have another question. I read up about FPGA circuits and i was under the asumption that you can program these circuits. What exactly can I program on them, am i able to program the frequency in which the dsp filters and am i able to program the op-amp to create a higher voltage and current.

berkeman
Mentor
So I was reading up about eval boards. And I have another question. I read up about FPGA circuits and i was under the asumption that you can program these circuits. What exactly can I program on them, am i able to program the frequency in which the dsp filters and am i able to program the op-amp to create a higher voltage and current.
FPGAs and CPLDs are configurable digital logic circuits. You write a program in some hardware definition language (HDL or AHDL or VHDL or Verilog, etc.), and compile that program targeted for the particular chip. More complex digital circuits require bigger chips with more gates, etc. inside them. The program will define the input and output pins of the device, and will generally contain code for one or more state machines.

Writing code for a DSP engine on a CPLD or FPGA is a pretty large undertaking, and not what one would typically do for a first project. It would be more straightforward to do the DESP code on the uC in a high level language like C. That said, Xilinx does offer some canned DSP resources for their FPGAs:

http://www.xilinx.com/products/design_resources/dsp_central/grouping/index.htm [Broken]

http://www.xilinx.com/publications/matrix/DSP_selection_guide1.pdf

BTW, that free Xilinx ISE development software is quite good, as long as you have about a spare GB of disk space on your PC.

As for the opamp, that will need to be a separate circuit on the eval board. CPLDs and FPGAs are for building digital circuits.

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Why, specifically do you need to D/A then A/D? Are you implementing a unique filter function? If you just want some filtering done, you can do that in the analog domain, with op-amps, or a specialty chip like: MF10CN - General purpose dual active filter (DIP-20 pkg) from Maxim.

thanks, that is a good idea to use a MF10CN. But when it comes to certain frequencies, do you have to program them or do they come pre-programed for a specific frequency in which to filter at.

Depends on how you set it up, and the capacitor values you select, etc. Can be set up as Low Pass, High Pass, Band Pass, or Band Reject. Read through the design sheet e.g. http://www.national.com/ds/MF/MF10.pdf" [Broken] to get an idea if this is right for you or not. If your filter is simple, an op-amp solution may be even easier, and there are many tutorials available on the web for this. Good luck!

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