Very Low Noise, High Frequency Active RC, Filter Building Block

The LT1568 is an easy-to-use, active-RC filter building block with rail-to-rail inputs and outputs. The internal capacitors of the IC and the GBW product of the internal low noise op amps are trimmed such that consistent and repeatable filter responses can be achieved. With a single resistor value, the LT1568 provides a pair of matched 2-pole Butterworth lowpass filters with unity gain suitable for I/Q channels.

By using unequal-valued external resistors, the two 2-pole sections can create different frequency responses or gains. In addition, the two stages may be cascaded to create a single 4-pole filter with a programmable response. Capable of cutoff frequencies up to 10MHz, the LT1568 is ideal for antialiasing or channel filtering in high speed data communications systems. The LT1568 can also be used as a bandpass filter.

The LT1568 features very low noise, supporting signal-to-noise ratios of over 90dB. It also provides single-ended to differential signal conversion for directly driving high speed A/D converters. The LT1568 has a shutdown mode that reduces supply current to approximately 0.5mA on a 5V supply.

The LT1568 is available in a narrow 16-lead SSOP package.

Applications

* Replaces Discrete RC Active Filters and LC Filter Modules

* Antialiasing/Reconstruction Filters

* Dual or I-and-Q Channels (Two Matched 2nd Order Filters in One Package)

* Single-Ended to Differential Conversion

* Video Signal Processing

* Up to 10MHz Center Frequency on a Single 3V Supply

* Easy to Use—A Single Resistor Value Sets Lowpass Cutoff Frequency (200kHz < fC < 5MHz), Unequal Resistor Values Extend Cutoff Frequency Up to 10MHz

* Extremely Flexible—Different Resistor Values Allow Lowpass Transfer Functions with or Without Gain

* SNR = 92dB (fC = 2MHz, 2VP-P)

* THD = –84dB (fC = 2MHz, 1VP-P)

* Internal Capacitors Trimmed to ±0.75%

* Single 4-Pole Lowpass Filter or Matched Pair of 2-Pole Lowpass Filters

* Can be Connected as a Bandpass Filter

* Single-Ended or Differential Output

* Operates from Single 3V (2.7V Min) to ±5V Supply

* Rail-to-Rail Input and Output Voltages