Modern wireless system design is usually a team effort, with RF engineers working on the front end and the baseband guys working on the digital back end. The trouble in receiver design, though, is at the interface where the downconverted signal at some IF must then be digitized and sent to the baseband section. This is a tricky area that neither the RF nor baseband engineers are generally prepared to attack. A mixed-signal expert is usually needed to build the critical interface.
With IFs well into the many megahertz range, special differential amplifier to converter matching circuits and critical printed-circuit board (PCB) layouts are required. Recognizing this problem, Linear Technology has come up with an IF receiver module that eliminates the need to design that special interface. The LTM9001 implements the signal chain from the filtered and downconverted IF to the analog-to-digital converter (ADC) output (see the figure).
This system-in-a-package (SiP) module consists of a differential input amplifier with a gain of 20 dB, a 162.5-MHz LC bandpass filter with a bandwidth of 50 MHz for anti-aliasing, and a 16-bit, 130-Msample/s ADC all on a common die in a land-grid array (LGA) package of 11.25 by 11.25 mm. Additionally, it includes all bypass capacitors and other needed discretes.
The amplifierâ??s input impedance is available in 50-, 200-, or 400-Ω versions. The ADCâ??s signal-to-noise ratio (SNR) is 72 dB, and its spurious-free dynamic range (SFDR) is 82 dB. The ADC outputs are either CMOS or low-voltage differential signaling (LVDS), pin selectable. The module operates from a 3.3-V supply and dissipates 1.65 W.
The really great news about this product is that it will be available in custom form. For example, you can select the input amplifier gain from 8-, 14-, 20-, or 26-dB choices. The IF range may be up to 300 MHz, and the ADC can be had in sampling rates from 10 to 160 Msamples/s. The anti-alias filter may also be a bandpass or low pass.
If youâ??re designing high-end basestations, satellite communications receivers, special communications receivers, spectrum analyzers, or other wireless test gear, the LTM9001 is worth an evaluation. Available now, it costs $82 in quantities of 1000 units. Contact the company for more details and quotes on your custom needs.
LINEAR TECHNOLOGIES www.linear.com