DEMO MANUAL DC2473A LTC6419 Dual Differential Amplifier/ADC Driver DESCRIPTION Demonstration circuit 2473A features the LTC 6419 Dual C3, C7, C14 and C18 can be replaced by 0 resistors to Differential Amplifier/ADC Driver. It incorporates a variety allow the DC bias to reach the outputs. of passive components to support configurations for var- By default, VOCMA and VOCMB are self-biased and float ied applications. These fully-differential amplifiers accept to a typical 1.25V on each of the common-mode pins single-ended or differential input with almost no difference + (with V = 5V). The VOCMA and VOCMB voltage of the in distortion performance. two amplifiers can be set independently with external DC The LTC6419 is a high speed dual differential amplifier with supply voltage source, or on board voltage dividers R18/ superior distortion and low noise, suitable for demanding R19 and R37/R38. communications transceivers, cellular base-stations and Enable (Shutdown) other high speed signal chain applications. Jumpers JP1 and JP2 control the enable functions of ADDITIONAL INFORMATION amplifiers A and B. When set to the EN position, the part will be on and draw normal operating current. In the DIS The DC2473A demo board is ready for use as-is and is de- position, the part will be in shutdown and draw a very signed for ease of use and with minimum modification. The small amount of leakage current. demo board has features that can be accessed by adding, removing or changing components on the board to config- Ground and V Connections CC ure for single-ended and/or differential inputs and outputs. DC2473A GND turret is not only connected to V of the By default, the board is configured to have dual single-ended LTC6419, it also serves as the demo boards ground. For inputs with transformers, J4 (IN1 ) and J6 (IN2 ) and dual best result, a low impedance return path to the power single-ended outputs with transformers, J1(OUT1 ) and supply from GND is recommended. Short, low impedance J7 (OUT2 ). Each of these ports is matched to 50 im - + wires to the V and GND connectors of DC2473A will yield pedance to facilitate direct connections to test equipment. the best performance from the LTC6419. Driving the Inputs DC-Coupled Schematic Notes It is possible to configure the DC2473A inputs differentially For a 50 external load, transformer T2 or T4 and the with DC coupling. Transformers and components at loca- series 100 resistors (R7, R9 or R26, R28) present each tions T1, T3, C2, C6, C13 and C17 connections should be amplifier with a 400 load impedance. These resistors replaced with 0 resistors. The inputs are now DC-coupled produce a 6dB voltage drop when driving loads. and can be driven single-ended or differentially (resistor Because the unmodified amplifier has 0dB voltage gain, values may be changed to balance the source impedances). and each transformer adds approximately 1dB insertion Changing the Output Common-Voltage loss, the total unmodified demo board will measure ap- proximately 8dB insertion loss from the input port (J4 or The turrets marked VOCM1 and VOCM2 (E2 and E4) J6) to the output port (J1 or J7). control the output (and input, if AC-coupled) common mode voltage of the DC2473A. This function can be used Design files for this circuit board are available at to level-shift the DC output voltage for optimum system DEMO MANUAL DC2473A QUICK START PROCEDURE Table 1 shows the function of each SMA connector on 2. Apply input signal or network analyzer to J4 (IN1 ) the board. Refer to Figure 1 for the connection diagram or J6 (IN2 ). DC2473As input is impedance matched and follow the procedure below: to50. 1. Connect the power supply as shown. The power labels 3. Observe the output via J1 (OUT1 ) or J7 (OUT2 ). The + of V and GND directly correspond to the power sup- output is impedance matched to 50, suitable for the ply. Typical current consumption of LTC6419 is about input of a network or spectrum analyzer. 104mA for both amplifiers. Jumpers JP1 and JP2 Table 1 shows the function of each input and output on enable or shut down the amplifier A and amplifier B, the board. respectively. Table 1. DC2473A Board I/O Descriptions CONNECTOR FUNCTION + J2 (IN1 )/J4 (IN1 ) Can be configured to either single-ended or differential input. + J6 (IN2 )/J8 (IN2 ) + J1 (OUT1 )/J3 (OUT1 ) Can be configured to either single-ended or differential output. With proper + J5 (OUT2 )/J7(OUT2 ) impedance matching, the device can be used to drive a network analyzer, spectrum analyzer or an ADC. E1 (VCM1), E3 (VCM2) The input common mode voltage. Leave open if unused. E2 (VOCM1), E4 (VOCM2) Output common mode adjust. By default, these pins are self-biasing within U1A and U1B. Leave open if unused. + E5 (V ) Positive Supply voltage source E8 (GND) Supply Ground dc2473af 2