DEMO CIRCUIT 1418 DEMO CIRCUIT 1418 QUICK START GUIDE LTC6604-X QUICK START GUIDE LTC6604-2.5, LTC6604-5, LTC6604-10 and LTC6604-15 Dual, Matched, Fully-Differential, Lowpass Filter DESCRIPTION Demonstration circuit 1418 features the LT6604-XX se- thth ries ofries of a du a dual, al, matchedmatched,, f fully differenully differenttial 4ial 4 or ordderer lolow-w- Table 1. The DC1418 Assemblies papassss filter filter approximating a Ch approximating a Chebyshev frequency re-ebyshev frequency re- sponsesponse. The . The cutoffcutoff frequ frequeencies (Fc) oncies (Fc) of f LT6604-XX are: LT6604-XX are: ASSEMBLY 2.52.5MMHHzz, 5, 5MMHHzz, 10, 10MHz and 15MHzMHz and 15MHz. (see Tab. (see Tablle e 1). 1). TheThe DC1418A-A LTC6604-2.5, Fc = 2.5MHz LT6604-XX combines a lowpass filter with two fullyLT6604-XX combines a lowpass filter with two fully DC1418A-B LTC6604-5, Fc = 5MHz differendifferenttial matched aial matched ammplifiers for driving the differ-plifiers for driving the differ- DC1418A-C LTC6604-10, Fc = 10MHz ential inputs of a dual analog to Digital Converter ential inputs of a dual analog to Digital Converter DC1418A-D LTC6604-15, Fc = 15MHz (ADC) and band-limiting the baseband signal of digi-(ADC) and band-limiting the baseband signal of digi- tal communital communications receiver. cations receiver. Each LT6604-XX filter IC Each LT6604-XX filter IC requrequires onires only tly twwo o extexternernaal inputl input resisto resistorrs to s to setset th the e fil-fil- Figure 1. The DC1418 Top Silk Screen ters diffters differential gain.erential gain. A DC1418 A DC1418 bbooaard contrd contains ains anan LT6604-XX configuLT6604-XX configurred wited with h input resistinput resistors as tors as twwo o uunitynity gagaiinn di differefferentiantial aml amplplifieifiersrs/low/lowpapassss filfiltterers.s. GaiGainns gs grreeaateterr than on than one re reeqquuirire che changangiingng the inp the inpuut rt reessiiss-- torstors to to a a lolowewer r vavaluelue ( (rrefeferer to anto an LT LTC660C6604-4-XX dXX daatata sh sheeteet andand thethe DC1 DC14418 sch18 scheemmataticic). ). ConnConnectectionion t to the o the diffdifferential erential input input and outputand output of of a a DC1DC1418 is 418 is ththrough SMA rough SMA connectors. On-board juconnectors. On-board jumpmpers ers configure the DC1418 foconfigure the DC1418 for r dual odual orr sin single suppgle supply oply opera-era- tion tion and and intinteernal ornal orr extexternal outputernal output common common (VOCM) (VOCM) modmodee biasing biasing.. The d The diifffferenerential inputial input of a DC141t of a DC1418 is 8 is AC AC coupled and coupled and can bcan bee con configurfigured fed for or DC coupling bDC coupling byy re-re- placing placing shoshorrttiing thng the inpue inputt cap capacitors acitors with zero ohwith zero ohms ms surfsurfacace-e-momoununt ret resisistostorr j juumpmperers. Ins. In addi additiontion, t, thhee DC1DC1418 has 418 has surfsurface-moace-moununt pads to adt pads to add input passive d input passive cocomponents mponents ffor inputor input sign signal al ffiilteringltering and and DC DC bbiiasingasing.. DesignDesign files ffiles for this or this circuitcircuit board are available. board are available. Call the LCall the LTTC factorC factoryy.. , LTC and LT are registered trademarks of Linear Technology Corporation. 1 DEMO CIRCUIT 1418 QUICK START GUIDE LTC6604-X QUICK TEST SET UP Dual Power Supply Oscilloscope (100MHz) Signal Generator with 50 Ohm Output 50 Ohm Terminator Figure 2. Dual Supply Test Set Up Connections (set the JP1 shunt to VMIDA and the JP2 shunt to DUAL). Quick Test Procedure 2. Testing the VinB to VoutB Signal Path. A DC1418 has two pairs of differential inputs, Connect signal generator to Vin+B and terminate Vin-B Vin+A/Vin-A and Vin+B/Vin-B and two pairs of differen- with a 50 ohm terminator. Set the generator for a 1MHz, tial outputs Vout-A /Vout+A and Vout-B/Vout-B. 2Vp-p, and sinewave. Connect oscilloscope channel 1 to Vout-B and channel 2 to Vout+B. The oscilloscope 1. Testing the VinA to VoutA Signal Path. channels connected to Vout-B and Vout+B show a Connect a DC1418 board as shown in Figure 2 (connect 1MHz, 1Vp-p, sinewave. signal generator to Vin+A and terminate Vin-A with a 50 ohm terminator). Set the generator for a 1MHz, 2Vp-p, Note 1: For unity gain testing the DC1418 inputs must and sinewave. The oscilloscope channels connected to be ideally driven by a zero ohm source (the outputs of a Vout-A and Vout+A show a 1MHz, 1Vp-p, sinewave (see high speed differential amplifier). However with the 50 Note 1). ohm impedance of the generators output and termina- tor is in series with the input resistors and the input to output gain is less than one. Note 2: For single supply testing set the JP2 shunt to SINGLE. 2