Datasheet LTC6421-20 (Analog Devices) - 10

LTC6421-20
APPLICATIONS INFORMATION
voltage with a 0.1μF bypass capacitor. When interfacing
Test Circuits
with A/D converters such as the LTC22xx families, the Due to the fully-differential design of the LTC6421 and VOCM pin can be connected to the VCM pin of the ADC. its usefulness in applications with differing characteristic specifi cations, two test circuits are used to generate the
Driving A/D Converters
information in this data sheet. Test Circuit A is DC1299, a The LTC6421-20 has been specifi cally designed to interface two-port demonstration circuit for the LTC6420/LTC6421 directly with high speed A/D converters. The back page of family. The schematic and silkscreen are shown in Fig- this data sheet shows the LTC6421-20 driving an LTC2285, ure 4. This circuit includes input and output transformers which is a dual 14-bit, 125Msps ADC. (baluns) for single-ended-to-differential conversion and The V impedance transformation, allowing direct hook-up to a OCM pins of the LTC6421-20 are connected to the V 2-port network analyzer. There are also series resistors CM pins of the LTC2285, which provide a DC voltage level of 1.5V. Both ICs are powered from the same 3V at the output to avoid loading the amplifi er directly with a supply voltage. 50Ω load. Due to the input and output transformers, the –3dB bandwidth is reduced from 1.3GHz to approximately The inputs to the LTC6421-20 can be confi gured in various 1.1GHz. ways, as described in the Input Impedance and Matching section of this data sheet. The outputs of the LTC6421-20 Test Circuit B uses a 4-port network analyzer to measure may be connected directly to the analog inputs of an ADC, S-parameters and gain/phase response. This removes the or a simple lowpass or bandpass fi lter network may be effects of the wideband baluns and associated circuitry, inserted to reduce out-of-band noise. for a true picture of the >1GHz S-parameters and AC characteristics. 642120fb 10 Document Outline FEATURES DESCRIPTION APPLICATIONS TYPICAL APPLICATION ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION ORDER INFORMATION SELECTOR GUIDE DC ELECTRICAL CHARACTERISTICS AC ELECTRICAL CHARACTERISTICS TYPICAL PERFORMANCE CHARACTERISTICS PIN FUNCTIONS BLOCK DIAGRAM APPLICATIONS INFORMATION TYPICAL APPLICATIONS PACKAGE DESCRIPTION REVISION HISTORY TYPICAL APPLICATION RELATED PARTS