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Integrated broadband filters and ADCs

Linear Technology has introduced a family of five single and dual active low-pass filters to drive ADCs in broadband wireless communications applications and signal processing equipment.

The LTC6603 is a dual matched programmable 9th order switched capacitor linear-phase filter and ADC driver, with cut-off to 2.5MHz. Gain and cut-off are adjustable via a serial SPI port or can be fixed by pin-strapping. Frequency control over a 100:1 range can be implemented using an external DAC to vary the device's master reference clock.

The second filter in the family, the LTC6601-1, is a lowpass active filter and ADC driver with configurable bandwidth from 5MHz to 28MHz. The filter has a 2nd order linear phase Butterworth response. It has differential inputs and outputs. The filter's on-chip resistors and capacitors that form its cutoff frequency, Q (quality factor of a filter) and gain are laser trimmed at the factory to an absolute tolerance of 0.5% typical. These resistors and capacitors are pinned out, allowing users to pin strap wide combinations of filter response and gain. The amplifier's frequency response is also laser trimmed to provide a highly accurate and repeatable filter response from device to device. Higher order filters can be attained by cascading multiple stages of the LTC6601-1.

Rounding out the family are the LTC6605-7, -10 and -14, which are fixed frequency, 2nd order linear phase dual matched lowpass active filters having bandwidths of 7MHz, 10MHz and 14MHz, respectively. Each filter pairs are tested and guaranteed to offer tight matching of phase and gain characteristics. These filters are ideal for I/Q demodulator channel filtering in WiMAX and broadband wireless access equipment including point-to-point microwave links. The matched filter performance is also suitable for driving multi-channel signal processing and pre-filtering for high speed ADCs.

The LTC6603 comes in a 4mm x 4mm 24-lead QFN package, and the LTC6601-1 in a same sized 20-lead QFN. The LTC6605 family comes in a 6mm x 3mm, 22 leads DFN package. All filters in the family are available in C grade specified for 0°C to 70°C, and I-grade specified for -40°C to 85°C operation.

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