Dual Lowpass Filter with Differential Amplifier and Guaranteed Matching

The LT6604-xx consists of two matched, fully differential amplifiers, combined with 4th order filters approximating a Chebyshev lowpass response. Each device offers guaranteed matched amplitude and phase characteristics, enhancing the performance of current and next generation wireless communication standards such as LTE (Long Term Evolution) and WiMAX, while addressing the challenge of channel matching.

These products offer best-in-class low distortion and low noise, supporting a high system signal-to-noise performance. The differential output stage of each filter is designed to drive directly into high-sampling rate A/D converters with minimum distortion and high signal-to-noise performance. Each amplifier has a minimum output swing of 2Vp-p and an adjustable common-mode voltage, allowing it to interface to a wide range of A/D converters. The small 4mm x 7mm package offers significant space savings compared to prior discrete solutions.

The LT6604-xx combines baseband channel filtering and gain matching to form a compact solution for high-performance I/Q demodulators. Additionally, these devices can be used as pre-filters for multichannel A/D converters. Each filter in the LT6604 offers better than 0.9dB of in-band gain flatness right up to the cutoff frequency. The 4th order Chebyshev filter provides sharp roll-off while exhibiting minimum group delay response. The filter characteristics are specified for 3V, 5V and ±5V supply operation. Each differential filter/amplifier gain can be set from 0dB to more than 12dB using a pair of external resistors.

The LT6604 draws a total quiescent supply current of 26mA per channel. All four devices are offered in a 34-lead, 4mm x 7mm QFN surface mount package with identical pinouts. Two grades are offered, including a commercial grade with guaranteed operation from 0°C to 70°C.