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IF amplifier touts low noise

Posted: 19 Dec 2008     Print Version  Bookmark and Share

Keywords:IF amplifier  dynamic range  OIP3  signal level 


Linear Technology Corp. has developed a broadband digitally programmable gain IF amplifier, featuring a 48dBm output 3rd order intercept (OIP3) at 200MHz.

The LT5554 has very low noise, enabling very high dynamic range performance in wireless communication receivers and signal processing systems. Its gain is digitally controlled from 2- to 18dB by a 7bit parallel word, producing the finest 0.125dB steps gain control granularity of any amplifier available.

The amplifier settles in less than 5ns from a gain change, producing low glitch noise and supporting very fast and accurate AGC (Automatic Gain Control) performance. Its output stage has robust capability to drive into 50Ω loads with low distortion and noise. Thus it enables high spurious-free dynamic range performance in ADC systems.

Unique to the LT5554 is its OIP3 performance, which remains consistently high over a wide varying signal level range. In contrast, the closest competing solution is limited to only a narrow ±dB signal level range. With the new generation of wireless technology such as Long-Term Evolution and WiMAX, which use modulated signals with 12dB crest-factor, the need to maintain linearity performance over wide operating levels is paramount for producing consistent base station performance. Additionally the LT5554 has high gain accuracy of ±0.1dB from -40°C to 85°C, which is a five time improvement over the closest competing offering, which has accuracy of ±0.5dB over similar temperature range.

The LT5554 is a full differential input and output amplifier. Its differential outputs can drive directly into 50Ω loads. The amplifier may be overdriven and can recover very quickly in less than 5ns. Additionally, the amplifier has excellent reverse isolation. These characteristics make the LT5554 a suitable amplifier to drive high speed, high resolution ADCs, where the input sampling noise can couple back to the RF and IF circuits.

The LT5554 is powered from a single 5V supply. It draws a nominal supply current of 200mA. The chip can be shutdown via an ENABLE pin. When in shutdown the device draws a typical supply current of 4mA, and a maximum of 5.1mA. The device comes in a 32-lead, 5mm x 5mm plastic QFN surface mount package. Prices for the LT5554 start at Rs.220.16 ($4.40) each in 1,000-piece quantities. The LT5554 is available immediately from stock.

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