Electronic Design

Digitally Programmable IF VGA Improves Signal Integrity

The LT5554 broadband digitally programmable gain IF amplifier from Linear Technology features a 48-dBm output third-order intercept (OIP3) at 200 MHz. It also boasts very low noise, enabling high-dynamic-range performance in wireless communication receivers and signal-processing systems.

A 7-bit parallel word digitally controls the device’s gain from 2 to 18 dB, producing the finest 0.125-dB steps gain control granularity of any amplifier available, according to the company. The LT5554 settles in less than 5 ns from a gain change, producing low glitch noise and supporting very fast and accurate automatic gain control (AGC) performance. Its output stage can drive into 50-O loads with low distortion and noise, enabling high spurious-free dynamic range performance in analog-to-digital converter (ADC) systems.

The LT5554’s OIP3 performance remains consistently high over a wide varying signal level range, while the closest competing solution is limited to a narrow ±1-dB signal level range, Linear says. Wireless technology like Long Term Evolution (LTE) and WiMAX use modulated signals with a 12-dB crest factor, requiring the maintenance of linearity performance over wide operating levels for consistent basestation performance.

The amplifier offers a ±0.1-dB gain accuracy from –40°C to 85°C, while the closest competing device has a ±0.5-dB accuracy over a similar temperature range, the company says. Linear also claims the LT5554 provides the finest 0.125-dB gain control step granularity of any IF amplifier on the market.

Additionally, the LT5554 is a full differential input and output amplifier. It may be overdriven, and it can recover in less than 5 ns. Linear also says it provides excellent reverse isolation, suiting it to drive high-speed, high-resolution analog-to-digital converters where the input sampling noise can couple back to the RF and IF circuits.

Powered by a single 5-V supply, the LT5554 draws 200 mA. It can be shut down via an ENABLE pin. When it shutdown, it draws a typical supply current of 4 mA and a maximum of 5.1 mA. It comes in a 32-lead, 5- by 5-mm plastic quad flat no-lead surface-mount package. Available immediately from stock, prices start at $4.40 each in 1000-piece lots.

Linear Technology


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