Electronic Design

RF/IF Amplifiers Drive High-Frequency ADCs With Low Distortion, High Linearity

The ADL5561 and ADL5562 amplifiers simplify the driving of 12- to-16-bit analog-to-digital converters (ADCs) in advanced wire-line and wireless communications systems. These ultra-low-distortion differential amplifiers efficiently drive the high-speed, high-IF sampling ADCs required by today’s advanced communications systems. Both are capable of maintaining performance while driving ADCs up to 500 MHz, exceeding the industry’s previous maximum of 380 MHz, set in 2005 by ADI’s AD8352 differential amplifier.

Thanks to the use of on-chip, user-selectable gain-setting resistors, ADI can provide detailed specifications at common IF frequencies (70, 100, 140, and 250 MHz) and common gain settings (6, 12, and 15.5 dB). This expedites the design process, provides greater flexibility, and allows the designer to exploit fully the amplifier’s performance at multiple gain settings and IF frequencies. Additionally, the pin-compatible ADL5561 and ADL5562 allow the user to select power consumption and performance to meet the requirements for a given application.

The amplifiers drive 12- to 16-bit ADCs at the highest practical IF frequencies for use in next-generation communications systems, such as 3G LTE (Long-Term Evolution) and NGMN (Next Generation Mobile Networks). Lowering the distortion level of the ADC driver improves system performance at higher frequencies by helping to maximize the receive channel’s spurious-free dynamic range (SFDR) and minimize its signal-to-noise-ratio (SNR).

This improvement minimizes the number of IF frequencies within the radio design, resulting in lower power, cost, component count, and board area, and advancing system-level performance in applications such as wireless base stations, cable communications, medical and instrumentation, military and satellite communications.

The 2-GHz ADL5561 ultra-low-distortion differential amplifier consumes just 40 mA, suiting it for use in sub-140 MHz IF applications. It achieves distortion levels of –86 dBc HD2, –88 dBc HD3, and –95 dBc IMD3 at 100 MHz. The 2.6-GHz ADL5562 ultra-low-distortion differential amplifier consumes 80 mA and achieves distortion levels of –95 dBc HD2, –86 dBc HD3, and –96 dBc IMD3 at 140 MHz.

Both the ADL5561 and ADL5562 operate on a 3-V power supply and are available in a space-saving 3- by 3-mm lead-frame chip-scale package (LFCSP). Furthermore, unlike conventional gallium-arsenide (GaAs) differential amplifiers, which often require the use of a transformer to perform the single-ended to differential conversion, the ADL5561 and ADL5562 can operate in fully differential circuits or provide the single-ended to differential conversion.

The ADL5561 and ADL5562 samples are available now. Production quantities will be available in April 2009. Both devices cost $3.68 each in lots of 1000.

Analog Devices Inc.


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