DEMO MANUAL DC2496A-A/DC2496A-B LTC6432-15 100kHz to 1000MHz Differential ADC Driver/IF/RF Amplifier Description Demonstration circuit 2496A features the LTC6432-15 ended inputs and outputs so that the LTC6432-15 perfor- differential ADC Driver/IF Amplifier. The LTC 6432-15 has mance may be evaluated with standard test equipment. a fixed power gain of 15.9dB and works from 100kHz The native LTC6432-15 has 100 differential source and to 1400MHz. It is part of the high linearity LTC643X-YY load impedances, so the demo circuit uses 2:1 transform- amplifier series. ers to convert the differential input/output impedances to 50 single-ended impedance. As a differential amplifier, the LTC6432-15 offers flat gain and impressive linearity from 100kHz to 1GHz using a Design files for this circuit board are available at single output bias network. Since high fidelity differen- DEMO MANUAL DC2496A-A/DC2496A-B o Demo Circuit 2496A is a high linearity, fixed gain amplifier. operation. The V pull-up networks (L1, L2, L3, L4, R1, CC It is designed for ease of use. The LTC6432-15 is inter- R5, R9 and R13) and the de-coupling capacitors (C2, C3, nally matched to 100 differential source and load imped- C4, C5, C19, C20, C21 and C22) provide the proper DC ances from 100kHz to 1400MHz. Due to the unpopularity bias to the RF OUT nodes. A single 5V supply is required of 100 differential test equipment, transformers have for the V pins on the device. CC been added to convert these impedances to single-ended A pair of stability networks have been added. They consist 50. Hence, demo boards with various transformers are of a 1F capacitor (C6 and C15) and 348 resistor (R4 built for corresponding working frequency ranges. The and R14) in parallel at the LTC6432-15 inputs to ensure frequency range of the 2496A evaluation circuit is limited low frequency stability. by these input and output transformers. There are provi- It is important to note that X8R capacitors are used in sions for installing various SMT transformers on either the RF signal path. The DC block and feedback caps have the top or bottom side of DC2496As PCB. been specified as X8R capacitors. High capacitance den- Because LTC6432-15 has a very wide working frequency sity (high capacitor values in a small package) typically range, no single transformer can cover its full 13 octave contribute distortion products due to their poor voltage frequency band. The DC2496A PCB is quite versatile. coefficient. Film and NPO capacitors have low distortion There are footprints for various transformers on the PCB. but are unwieldy at 1F values. As a compromise we have Two demo board versions cover most commonly used found that X8R capacitors exhibit low distortion at reason- frequencies as shown in Table 1. able capacitance densities. Table 1. Frequency Ranges and Suggested 2:1 Transformers. If the user is concerned with thermal heating and the DC NUMBER FREQUENCY TRANSFORMERS MANUFACTURER associated reliability, the chip provides a means to deter- (MHz) PART mine the chip temperature. The T DIODE pin (turret E4) 2496A-A 0.1 to 20 SYTX2-6T-1+ can be forward biased to ground with 1mA of current. The 2496A-B 1 to 250 ADT2-1T+ Mini-Circuits measured voltage will be an indicator of the chip junction -- 20 to 400 ADT2-1T-1P+ temperature (T ). J -- 200 To 950 ADTL2-18+ Please note that eight DNC pins are connected on the Please note that the suggested frequency bands are demo board. These connections are not utilized for normal narrower than small-signal S-Parameters would indicate. operation and should be left open circuit on the final PCB. At the edges of their useful band, these transformers contribute distortion that degrades the performance of Table 2 shows the function of each input and output on the LTC6432-15. the board. Table 2. DC2496A board I/O descriptions Figure1 and Figure2 show demo board DC2496A-A and DC2496A-B schematics. Each demo circuits sche- CONNECTOR FUNCTION matic shows the required passive support components. J1 (IN) Single-ended input. Impedance matched to 50. Drive from a 50 network analyzer or signal source. At the boards inputs and outputs are the low frequency J4 (OUT) Single-ended output. Impedance matched to 50. transformer, SYTX2-6T-1+ or the mid-frequency trans- Drives a 50 network analyzer or spectrum analyzer. former, ADT2-2T+. Each of these transformers has a 1:2 E4 (T DIODE) When forward biased, the measured voltage will be an impedance transformation ratio. The input and output DC indicator of the chip junction temperature (T ). J blocking capacitors (C7, C9, C12 and C17) are required E2 (V ) Positive supply voltage source. CC because this device is internally DC-biased for optimal E3 (GND) Supply ground. dc2496aaf 2 peration