Demonstration circuit DC675C is for the evaluation of filter circuits using an LT1568. The LT1568 is a dual 2nd order active-RCfilterbuildingblockwithprecision ±0.75% capacitors and low noise op amps with 180MHz GBW trimmed to ±10% maximum variation. The ±10% GBW variation of the LT1568 op amps allows for minimizing the higher frequency error by decreasing resistor values. The cutoff or center frequency (fC) range of an LT1568 filter is 200kHz to 10MHz (5MHz for a bandpass filter). The low limit of 200kHz was chosen only to minimize resistor noise and DC offsets (using external capacitors the fC frequency can be less than 200kHz).
For testing and evaluation, the DC675C assembly is configured as a single 4th order, 500kHz narrow passband bandpass filter.
For other possible LT1568 configurations, the DC675C has unused pads for 0805 surface mount resistors and capacitors preconfigured with PCB traces to allow for the following high accuracy LT1568 filter circuits:
- 4th order lowpass filter
- 5th order lowpass filter
- 4th order narrow passband bandpass
- 4th order wide passband bandpass
- 4th order highpass filter
Refer to the LT1568 data sheet for additional information about filter circuit configurations.