20-dB gain broadband differential amplifier with high linearity

October 17, 2014 // By Graham Prophet
LTC6430-20 is a 20 MHz to 2 GHz differential input and output 20 dB gain amplifier that offers linearity of +51dBm OIP3 (output third order intercept) and 2.9 dB noise figure at 240 MHz.

It has OP1dB (output 1-dB compression point) of +23.9 dBm. The LTC6430-20 is offered in an A-grade version, which is 100% tested and guaranteed to a minimum OIP3 of +44.8 dBm, with a typical of +48.3 dBm at 380 MHz. Its gain is also guaranteed at minimum of 19.6 dB and maximum of 22.1 dB. A B-grade version offers a typical OIP3 of +46.3 dBm at the same frequency.

The LTC6430-20 is suitable for amplifying IF and RF signals in low distortion, high dynamic range transmitters or receivers at frequencies to 1.5 GHz. Higher frequencies up to 2 GHz can be achieved with appropriate impedance matching. The LTC6430-20's linearity characteristics are particularly notable when the device is used as an IF amplifier driving differential inputs of high speed A/D converters in main receivers or digital predistortion receivers whose performance relies on low distortion and high dynamic range. The device is suitable as a low noise amplifier for a wide range of broadband and narrowband radios that operate in the VHF/UHF bands, such as broadcast equipment, cable networks, white space broadband data services and low-band LTE/LTE-Advanced wireless base stations.

Both inputs and outputs of the LTC6430-20 are internally 100Ω matched differential from 20 MHz to 1.2 GHz, and have a 20.5 dB power gain with a frequency response flatness of better than 0.5 dB over that frequency range. The internal 100Ω matching simplifies design and allows easy cascading for higher gains, requiring minimum external components. Moreover, the differential configuration produces exceptionally low 2nd order harmonic distortion. For instance, at 380MHz, the 2nd order harmonic spur is -70 dBc relative to the fundamental.

Produced using an advanced SiGe BiCMOS process, the LTC6430-20 offers inherently stable performance, tolerating wide variations in power supply voltage and temperature. The device is specified for a case operating temperature range from -40°C to 85°C. It comes in a 4 x 4 mm QFN package, and is powered