DEMO CIRCUIT DC1264 QUICK START GUIDE DEMO CIRCUIT 1264 LOW NOISE, LOW DISTORTION DIFFERENTIAL IF AMPLIFIER QUICK START GUIDE LTC6410-6 Differential IF Amplifier Four-Port Test Board DESCRIPTION Demonstration circuit 1264 features the LTC6410-6 low stations, and other high-speed signal chain applications. noise, low distortion differential Intermediate Frequency (IF) The LTC6410-6 features a fully differential input and output Amplifier. This second evaluation board is meant for four- and is capable of directly driving a 50 load. One standout port network analysis or in-circuit evaluation with a minimal feature of the LTC6410-6 is the ability to independently ad- number of board parasitic to achieve the full performance of just the input impedance with two resistors at the inputs. the LTC6410-6. For a general-purpose evaluation board This allows the user to easily enhance the noise figure and for the LTC6410-6, obtain Demo Circuit 1103. power gain of the system for optimal performance. Design files for this circuit board are available. Call The LTC6410-6 is a high-speed differential amplifier with the LTC factory. superior distortion and noise performance, perfect for de- , LTC and LT are registered trademarks of Linear Technology Corporation. manding communications transceivers, cellular base- QUICK START PROCEDURE Table 1 shows the function of each SMA connector on the 3. Observe the output via J4 and J3. The output is capa- board. Refer to Figure 1 and follow the procedure below: ble of driving a 50 load, such as the input of a net- work or spectrum analyzer. 1. Connect the power supply to the VCC and GND turrets Table 1: DC1264 Connector Descriptions on the board. The LTC6410-6 accepts supply voltages CONNECTOR FUNCTION from 2.8-5.25V. The power supply must be capable of J1 (-IN) Differential Input. AC-Coupled by capacitor C1. J2 (+IN) Differential Input. AC-Coupled by capacitor C2. supplying at least 150mA. The GND turret is directly TP1 (VOCM) Self-Bias Voltage Adjust. Corresponds to VBIAS pin of connected to the board ground for single-supply oper- LTC6410. By default, 1.45V is supplied to this pin by ation. two resistors (VCC=3V). Override this voltage with any low-impedance DC voltage source. 2. Apply an input signal to J2 and J1. The input is fully J3 (-OUT) Differential Output. AC-Coupled by capacitor C3. differential and impedance-matched to 50 by default J4 (+OUT) Differential Output. AC-Coupled by capacitor C3. no external termination is necessary. Resistors R1 and R2 can be used to change the input impedance of the LTC6410. 1 DEMO CIRCUIT DC1264 QUICK START GUIDE LOW NOISE, LOW DISTORTION DIFFERENTIAL IF AMPLIFIER Figure 1. DC1264 Four-Port Evaluation Board ADDITIONAL INFORMATION Although the DC1264 demo board is designed for use with DC-COUPLING THE INPUTS/OUTPUTS four-port network analyzers, it can also be used for in- It is possible to DC-couple the LTC6410 in the signal chain. circuit evaluation of the LTC6410-6, This and other impor- Capacitors C1-C2 and C3-C4 should be replaced with 0 tant board information are included in this section. resistors. The inputs must be biased to within the com- mon-mode range of the LTC6410. SMA CONNECTOR SPACING The input and output SMA connectors are spaced 0.6 The common-mode voltage at the LTC6410 inputs will propagate through to the outputs. The resistive load to (15.24mm) apart, suitable for direct connection to the DC1119 demo board for Linear Technologys LT5527, ground at each output should be considered so that exces- LT5557, and LT5559 high linearity downconverting mixers. sive current is not drawn from the outputs when DC- coupled. A differential R should be used instead to LOAD avoid large quiescent load currents. ADJUSTING THE INPUT IMPEDANCE CHANGING THE BIAS VOLTAGE The input impedance of the LTC6410 can be adjusted in the range of 58-2000 by replacing R1 and R2 with equal- Turret TP1 controls the self-bias voltage of DC1264. This value non-zero resistors. The correct resistor value for the function can be used to bias the next stage for optimum desired differential input impedance is: system performance. By default, internal resistors supply 1.45V to the V pin (with V =3.0V). This voltage can be BIAS CC ()3810 Z 220000 DIFF over-ridden with an external voltage source at TP4 and/or R,R = 1 2 by DC-coupling the inputs of the LTC6410. 2000 Z DIFF Adjusting the input impedance too high may affect the performance of the part. See the LTC6410 datasheet. 2