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RF/IF Amplifiers
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15V buck-boost converters with ultralow 1.3µA IQ 15 inverting DC/DC controller converts a positive input to a negative output with a single inductor 20 improve solar battery RF/IF Amplifiers with OIP3 of 47dBm/50dBm at 240MHz Ease Implementation, Guarantee Performance Greg Fung charger efficiency in low light 24 replace halogen bulbs with LEDs in 24VAC and 12VAC lighting systems 28 Our communication infrastructure’s limited bandwidth is nearly filled to capacity by our increasing thirst for data transmitted via smartphone, TV, GPS and Wi-Fi. To quench this thirst, communications architects define systems that pack increasingly more data into limited bandwidth, but data rate improvements come at a price: the need for increasingly higher fidelity transmit and receive signal chains. When it comes to amplifiers, low noise and high linearity are required to faithfully reproduce a signal without degrading the original signal. At low signal powers, undesired noise must be low enough to allow the intended signal to rise above the noise floor. At high signal levels, a linear amplifier must prevent unwanted harmonics and intermodulation products from masking the intended signal. The LTC®6431-15 and LTC6430-15 achieve both of these goals. The LTC6431-15 and LTC6430-15 are two fixed gain amplifiers that feature very high OIP3 (linearity) with very low associated noise. The LTC6431-15 is a singleended radio frequency (RF)/intermediate frequency The LT®3795 LED driver reduces peak EMI without incurring LED flicker. See page 12. Caption

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The LTC6431-15 boasts a typical OIP3 of 47dBm at 240MHz— essentially hammering the intermodulation products (IM3) into the noise floor so they don’t interfere with the intended signals. (LTC6430/1-15 continued from page 1) DESIRED TONE DESIRED SIGNAL For instance, if a single tone is injected into a nonlinear amplifier, the result is the desired tone plus its harmonics. Normally, these harmonics can be filtered out, as they are far enough in frequency from the desired tone. If two tones are injected into of an issue, but an amplifier’s linearity becomes increasingly important. Linearity...

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design features The single-ended LTC6431-15 excels as an IF amplifier to overcome filter losses, or as an ADC driver when used with a balun transformer. With its wide bandwidth, the LTC6431-15 can cover the entire CATV band. Z1 Figure 5. Adding matching networks to the input and output INPUT MATCH OUTPUT MATCH OUTPUT Z = 50Ω TRADITIONAL RF AMPLIFIER a nonlinear amplifier, the result is a far more complicated mix of the two desired tones and a multitude of unwanted tones, including harmonics of the two tones, the sum and difference of the two input tones, and other intermodulation products....

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The LTC6430-15 excels as an ADC driver for high speed, high resolution ADCs. The challenge in these applications is to drive the unbuffered ADC inputs to their required input voltage levels while preserving the signal-tonoise ratio (SNR) and spurious free dynamic range (SFDR) of the ADC. Figure 8. Simplified schematic of wideband differential 14-bit ADC driver HIGH LINEARITY SOLVES THE TOUGHEST COMMUNICATION PROBLEMS The LTC6431-15 boasts a typical OIP3 of 47dBm at 240MHz —essentially hammering the IM3 products into the noise floor so that they don’t interfere with the intended signals...

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design features Figure 10. 500MHz single tone SFDR and SNR of LTC6430-15 and LTC2158 driver/ADC combo board (SNR = 61.5dB, SFDR = 75.7dB) to the system impedance, normally 50Ω (Figure 5). These matching networks in turn alter the amplifier’s NF and OIP3— often compromising the NF and OIP3 to achieve a reasonable impedance match. The LTC6431-15 and LTC6430-15 amplifiers internally match their input and output impedance over the 20MHz –1700MHz band, simplifying design while preserving their NF and OIP3. The single ended LTC6431-15 is internally input and output matched to 50W, whereas the...

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Using an appropriate pair of 2:1 balun transformers, the LTC6430-15 provides wideband amplification with low noise and low distortion. In this balanced configuration, the amplifier is matched to 50Ω at the input and output. The balanced configuration also has the advantage of suppressing 2nd order distortion which is critical in multi-octave wideband applications. BALUN_A = ADT2-1T FOR 50MHz TO 300MHz BALUN_A = ADT2-1P FOR 300MHz TO 400MHz BALUN_A = ADTL2-18 FOR 400MHz TO 1300MHz ALL ARE MINI-CIRCUITS CD542 FOOTPRINT signals up to 2GHz. Op amps typically struggle to operate above 200MHz....

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design features A single balun cannot cover the entire LTC6430-15 band of operation. Linear offers several evaluation circuits that cover the amplifier’s intended bandwidth. Conveniently transformed to 50Ω at the input and output(s) for ease of bench characterization, these evaluation circuits also demonstrate the performance of the LTC6430-15 when used in a purely differential application without the baluns. Figure 13. Evaluation circuit of balanced amplifier shown in Figure 12: 50MHz–300MHz (ADT2-1T baluns) 54 Figure 14. Evaluation circuit of balanced amplifier shown in Figure 12:...

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Cable TV offers unique challenges for an amplifier. A high channel count requires excellent 3rd order linearity and due to the multiple octave environment, 2nd order products must be suppressed as well. The LTC6430-15 meets these challenges using a pair of 1.33:1 baluns to transform its inherent 100Ω differential impedance to 75Ω. ADC Driver Table 1 displays minimal degradation of SNR and SFDR for this high speed, high resolution ADC. The LTC6430-15’s high linearity (Figures 10 and 11) and low noise allow the designer to drive the ADC with minimal filtering at the ADC input. All...

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design features The LTC6431-15 and LTC6430-15 are manufactured using a high performance SiGe BiCMOS process, compared to other RF gain blocks manufactured using GaAs transistors. Using a silicon-based process yields better reproducibility over comparable GaAs processes. A BiCMOS process also allows Linear to integrate distortion cancellation, bias control and voltage regulator functions into the devices. SILICON-BASED PROCESS FOR BETTER REPRODUCIBILITY The LTC6431-15 and LTC6430-15 are manufactured using a high performance SiGe BiCMOS process, compared to other RF gain blocks manufactured...

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