LMH6515EVAL

User's Guide SNOA482B – September 2007 – Revised May 2013 AN-1580 LMH6515EL Digital Controlled, Variable Gain Amplifier Evaluation Board 1 General Description The LMH6515EL evaluation board is designed to aid in the characterization of Texas Instruments high speed LMH6515 digital controlled, variable gain amplifier. Use the evaluation board as a guide for high frequency layout and as a tool to aid in device testing and characterization. 2 Basic Operation The LMH6515 DVGA has differential inputs and differential outputs. The LMH6515 will also support single ended to differential conversion with no transformer required on the input. To aid evaluation with 50 Ω single ended test equipment the LMH6515EL evaluation board provides for input and output transformers. For driving the evaluation board from a differential source, symmetrical signal paths are provided. Both input and output paths support fully differential signal paths. For component locations, see the schematic in Figure 1. The evaluation board uses end-mounted SMA connectors. On the IN+ input, resistor R1 provides input termination. The analog supply (VCCA) can be from 4 V to 5.25 V. The capacitor C5 is a supply bypass capacitor and should be low ESR ceramic. Resistors R11 and R12 as well as capacitor C4 should be left empty. The LMH6515EL evaluation board is designed for transformers wtih DC isloation between the primary and secondary windings. If baluns (transmission line transformers with no DC blocking) are used make sure to have DC isolation for all transformer pads. Transformer T1 can provide both impedance matching as well as single ended to differential conversion. The 2:1 (4:1 impedance) transformer matches 50 Ω equipment with the 200 Ω input impedance of the LMH6515 DVGA and there is an optional capacitor at C3, if additional stability is required. Do not connect the transformer secondary winding directly to ground. The LMH6515 has a self biased input common mode voltage of approximately 1.3 V. The amplifier will bias up to the optimal input common mode point. The resistors R2, R24, and R25 are normally left empty. These resistors can be used to force the LMH6515 input common mode to a value different than it's self biased state. Most applications will not require this function. If using a transmission line transformer for T1, capacitor C1 is necessary to preserve the proper input common mode voltage. For single ended inputs to the amplifier see Figure 7 and Figure 8 The LMH6515EL evaluation board is shipped with a transformer to facilitate testing with single ended equipment. To drive the LMH6515 evaluation board with a differential signal transformer T1 must be removed. Then, load capacitor C1 and C16 and cut the trace connecting the capacitor C2. R1 and R5 should be loaded with appropriate valued resistors (normally 50Ω). The C3 capacitor is not needed for this case and the transformer pads should be shorted with a low inductance wire: pad 6 to pad 1 and pad 4 to pad 3. On the output side of the board is transformer T2. C11 isolates the output common mode voltage from the output transformer primary windings. The output coupling capacitors C13 and C14 are necessary for Balun transformers which provide no DC isolation between the primary and secondary windings, and are also necessary when driving differential loads. All trademarks are the property of their respective owners. SNOA482B – September 2007 – Revised May 2013 Submit Documentation Feedback AN-1580 LMH6515EL Digital Controlled, Variable Gain Amplifier Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 1 Basic Operation www.ti.com For differential output signals remove transformer T2. Capacitor C11 can be left empty. Do not install resistor R4. Using the transformer T2 pads, place coupling capacitors between pads 3 and 4 and between pads 1 and 6 where the transformer would have been. These should be low ESR ceramic capacitors with a value of 1nF. These output coupling capacitors are necessary to isolate the output common mode voltage of the LMH6515 from the test equipment. The pads for capacitors C13 and C14 can be used as series output matching resistors. There is no copper between transformer pad #6 and C14. A low impedance short will have to be added manually. Resistors R3 and R4 are normally left empty in this configuration. The evaluation board supports two gain options. As shipped the evaluation board provides for a low gain, 200 Ω output impedance configuration. In order to use the high gain 400 Ω configuration, the traces from pins 13 and 16 to VCCA can be cut. For a detail of the trace cuts required, see Figure 6. SW1 is used to set the five gain control bits. When the latch position of SW1 is in 0 or OFF position, changes in the gain 0 to gain 5 bits are processed by the LMH6515. When the latch switch is in 1 or ON position, the last loaded state is held and gain bit switch changes have no affect. Landings for SMA connectors are also provided for high speed triggering of the gain bits. The LMH6515EL evaluation board is a four layer board; all four layers are detailed in Figure 2 through Figure 5. 2 AN-1580 LMH6515EL Digital Controlled, Variable Gain Amplifier Evaluation Board SNOA482B – September 2007 – Revised May 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Basic Operation www.ti.com SW1-A 7 1 + 6 C15 10P D1 1N5818M GND SW1-F VCCA VCCA 12 VCCA POWER SUPPLY CONNECTIONS R18 4.99k LATCH R21 4.99k GAIN0 R20 10k R23 10k VCCA R11 A/R 9 1 1n C13 L1 1 PH 3 15 C11 14 13 DAP C8 1n C9 0.01P C17 L2 1n 1 PH R16 4.99k VCCA 1 6 C14 OUT- 1n VCCA R4 is shorted on the PC Board R4 0 R17 10k 11 VCCA R13 4.99k R10 4.99k GAIN2 R14 10k SW1-C 9 SW1-D 4 R9 10k 2 A/R 3 GAIN3 C18 0.01P 2 R7 4.99k 1n VCCA 10 R6 10k R2 A/R 4 OUT+ VCCA GAIN1 TP1 R24 A/R C7 R3 A/R T2 TC4-1W SW1-B R25 A/R 0.01P 16 GAIN4 8 C2 is shorted on the PC Board LOAD + C2 A/R VCCA OUT+ GND2 3 5 1n R5 A/R 4 GAIN_4 C16 OUT - U1 IN- SW1-E IN- 8 IN+ GAIN_1 7 C6 12 C3 A/R LOAD - 11 2 6 GND1 GAIN_3 5 GAIN_0 1 R1 A/R GAIN_2 6 1n NC T1 TC4-1W C1 10 IN+ 2 VCCA 3 A/R LATCH 1n C4 4 C5 VCC R12 A/R VCCA GND TEST POINTS GND1 GND2 Figure 1. LMH6515EL Evaluation Board Schematic SNOA482B – September 2007 – Revised May 2013 Submit Documentation Feedback AN-1580 LMH6515EL Digital Controlled, Variable Gain Amplifier Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 3 Basic Operation www.ti.com Figure 2. Evaluation Board Top Layer Figure 3. Evaluation Board Bottom Layer 4 AN-1580 LMH6515EL Digital Controlled, Variable Gain Amplifier Evaluation Board SNOA482B – September 2007 – Revised May 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Basic Operation www.ti.com Figure 4. Evaluation Board Layer 2 Figure 5. Evaluation Board Layer 3 SNOA482B – September 2007 – Revised May 2013 Submit Documentation Feedback AN-1580 LMH6515EL Digital Controlled, Variable Gain Amplifier Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 5 Basic Operation www.ti.com Figure 6. Trace Cuts for High Gain (400 Ω Load) Operation Figure 7. Single Ended Input – No Transformer 6 AN-1580 LMH6515EL Digital Controlled, Variable Gain Amplifier Evaluation Board SNOA482B – September 2007 – Revised May 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Basic Operation www.ti.com VCC VCM = 1.4V C1 LMH6515 RIN = R1 || 200 200 VIN R1 5 WITHOUT THIS CAPACITOR THE INPUT WILL NOT FUNCTION GAIN 1-5 LATCH Figure 8. Schematic for Single Ended Input SNOA482B – September 2007 – Revised May 2013 Submit Documentation Feedback AN-1580 LMH6515EL Digital Controlled, Variable Gain Amplifier Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 7 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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