LT Very Low Noise, Differential Amplifi er and 2.5MHz Lowpass Filter FEATURES DESCRIPTION APPLICATIONS TYPICAL APPLICATION

Transcription

1 FEATURES n ±.db (Max) Rippe 4th Order Lowpass Fiter with.mhz Cutoff n Programmabe Differentia Gain via Two Externa Resistors n Adjustabe Output Common Mode otage n Operates and Specifi ed with,, ± Suppies n 8dB S/N with Suppy and RMS Output n Low Distortion, RMS, 8Ω Load MHz: 9dBc nd, 88dBc rd n Fuy Differentia Inputs and Outputs n Compatibe with Popuar Differentia Ampifi er Pinouts n SO-8 and DFN- Packages APPLICATIONS n High Speed ADC Antiaiasing and DAC Smoothing in Networking or Ceuar Basestation Appications n High Speed Test and Measurement Equipment n Medica Imaging n Drop-in Repacement for Differentia Ampifi ers L, LT, LTC, LTM, Linear Technoogy and the Linear ogo are registered trademarks of Linear Technoogy Corporation. A other trademarks are the property of their respective owners. TYPICAL APPLICATION -BIT 4kHz to.mhz DISCRETE MULTI-TONE SIGNAL AT MSPS LADCOM I OUT A LTC8 I OUT B CLK DAC Output Fiter MHz.Ω.Ω 8Ω 8Ω DESCRIPTION LT-. ery Low Noise, Differentia Ampifi er and.mhz Lowpass Fiter (S8 Pin Numbers Shown).μF 4 7 LT-. 8.μF OUT OUT TAa (dbm) The LT -. combines a fuy differentia ampifier with a 4th order.mhz owpass fiter approximating a Chebyshev frequency response. Most differentia ampifiers require many precision externa components to tai or gain and bandwidth. In contrast, with the LT-., two externa resistors program differentia gain, and the fiter s.mhz cutoff frequency and passband rippe are internay set. The LT-. aso provides the necessary eve shifting to set its output common mode votage to accommodate the reference votage requirements of A/Ds. Using a proprietary interna architecture, the LT-. integrates an antiaiasing fiter and a differentia ampifier/driver without compromising distortion or ow noise performance. At unity gain the measured in band signato-noise ratio is an impressive 8dB. At higher gains the input referred noise decreases so the part can process smaer input differentia signas without signifi canty degrading the output signa-to-noise ratio. The LT-. aso features ow votage operation. The differentia design provides outstanding performance for a 4 P-P signa eve whie the part operates with a singe suppy. The LT-. is avaiabe in SO-8 and DFN- packages. For simiar devices with higher cutoff frequency, refer to the LT-, LT-, LT- and LT- data sheets. DAC Output Spectrum BASEBAND SIGNAL 4 DAC OUTPUT IMAGE (dbm) LT-. Output Spectrum FREQUENCY (MHz) TAb FREQUENCY (MHz) TAc fe

2 LT-. ABSOLUTE MAXIMUM RATINGS Tota Suppy otage... Input Current (Note 8)...±mA Operating Temperature Range (Note )... 4 C to 8 C Specifi ed Temperature Range (Note 7)... 4 C to 8 C (Note ) Junction Temperature... C Storage Temperature Range... C to C Lead Temperature (Sodering, sec)... C PIN CONFIGURATION TOP IEW IN IN NC NC OCM MID 4 9 NC OUT 8 7 OUT DF PACKAGE -LEAD (4mm 4mm) PLASTIC DFN T JMAX = C, θ JA = 4 C/W, θ JC = 4 C/W EXPOSED PAD (PIN ) IS, MUST BE SOLDERED TO PCB TOP IEW IN OCM OUT IN MID OUT S8 PACKAGE 8-LEAD PLASTIC SO T JMAX = C, θ JA = C/W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LTCS8-.#PBF LTCS8-.#TRPBF 8-Lead Pastic SO C to 7 C LTIS8-.#PBF LTIS8-.#TRPBF I 8-Lead Pastic SO 4 C to 8 C LTCDF-.#PBF LTCDF-.#TRPBF -Lead (4mm 4mm) Pastic DFN C to 7 C LTIDF-.#PBF LTIDF-.#TRPBF -Lead (4mm 4mm) Pastic DFN 4 C to 8 C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LTCS8-. LTCS8-.#TR 8-Lead Pastic SO C to 7 C LTIS8-. LTIS8-.#TR I 8-Lead Pastic SO 4 C to 8 C Consut LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a abe on the shipping container for the DFN Package. Consut LTC Marketing for information on nonstandard ead based fi nish parts. For more information on ead free part marking, go to: For more information on tape and ree specifi cations, go to: ELECTRICAL CHARACTERISTICS The denotes the specifications which appy over the fu operating temperature range, otherwise specifications are at T A = C. Uness otherwise specified S = ( =, = ), R IN = 8Ω, and R LOAD = k. PARAMETER CONDITIONS MIN TYP MAX UNITS Fiter Gain, S = IN = P-P, f IN = DC to khz...4 db R IN = 8Ω IN = P-P, f IN = 7kHz (Gain Reative to khz).. db IN = P-P, f IN =.9MHz (Gain Reative to khz)... db IN = P-P, f IN =.MHz (Gain Reative to khz)... db fe

3 LT-. ELECTRICAL CHARACTERISTICS The denotes the specifications which appy over the fu operating temperature range, otherwise specifications are at T A = C. Uness otherwise specified S = ( =, = ), R IN = 8Ω, and R LOAD = k. PARAMETER CONDITIONS MIN TYP MAX UNITS IN = P-P, f IN =.MHz (Gain Reative to khz)..9 db IN = P-P, f IN = 7.MHz (Gain Reative to khz) 4 db IN = P-P, f IN =.MHz (Gain Reative to khz) db Fiter Gain, S = IN = P-P, f IN = DC to khz...4 db R IN = 8Ω IN = P-P, f IN = 7kHz (Gain Reative to khz).. db IN = P-P, f IN =.MHz (Gain Reative to khz)... db IN = P-P, f IN =.MHz (Gain Reative to khz)... db IN = P-P, f IN =.MHz (Gain Reative to khz)..9 db IN = P-P, f IN = 7.MHz (Gain Reative to khz) 4 db IN = P-P, f IN =.MHz (Gain Reative to khz) db Fiter Gain, S = ± IN = P-P, f IN = DC to khz...4 db Fiter Gain, R IN = 4Ω IN =. P-P, f IN = DC to khz, S = IN =. P-P, f IN = DC to khz, S = IN =. P-P, f IN = DC to khz, S = ± db db db Fiter Gain Temperature Coeffi cient (Note ) f IN = khz, IN = P-P 78 ppm/ C Noise Noise BW = khz to.mhz μ RMS Distortion (Note 4) MHz, RMS, R L = 8Ω nd Harmonic rd Harmonic Differentia Output Swing Measured Between Pins 4 and S = S = dbc dbc P-P DIFF P-P DIFF Input Bias Current Average of Pin and Pin 8 μa Input Referred Differentia Offset R IN = 8Ω, Differentia Gain = / S = S = S = ± R IN = 4Ω, Differentia Gain = 4/ S = S = S = ± Differentia Offset Drift μ/ C Input Common Mode otage (Note ) Differentia Input = m P-P, S =.. R IN 4Ω S = S = ±.... Output Common Mode otage (Note ) Differentia Input = P-P, S = Pin 7 = Open S = S = ± Output Common Mode Offset (with Respect to Pin ) S = S = S = ± Common Mode Rejection Ratio db otage at MID (Pin 7) S = (S8) S = (DFN) S = MID Input Resistance kω OCM Bias Current OCM = MID = S / S = S = Power Suppy Current S =, S = S =, S = S = ± m m m m m m m m m μa μa ma ma ma fe

4 LT-. ELECTRICAL CHARACTERISTICS Note : Stresses beyond those isted under Absoute Maximum Ratings may cause permanent damage to the device. Exposure to any Absoute Maximum Rating condition for extended periods may affect device reiabiity and ifetime. Note : This is the temperature coeffi cient of the interna feedback resistors assuming a temperature independent externa resistor (R IN ). Note : The input common mode votage is the average of the votages appied to the externa resistors (R IN ). Specifi cation guaranteed for R IN 4Ω. For ± suppies, the minimum input common mode votage is guaranteed by design to reach. Note 4: Distortion is measured differentiay using a singe-ended stimuus. The input common mode votage, the votage at OCM, and the votage at MID are equa to one haf of the tota power suppy votage. Note : Output common mode votage is the average of the votages at Pins 4 and. The output common mode votage is equa to the votage appied to Pin. Note : The LTC-. is guaranteed functiona over the operating temperature range of 4 C to 8 C. Note 7: The LTC-. is guaranteed to meet specifi ed performance from C to 7 C and is designed, characterized and expected to meet specifi ed performance from 4 C and 8 C, but is not tested or QA samped at these temperatures. The LTI-. is guaranteed to meet specifi ed performance from 4 C to 8 C. Note 8: The inputs are protected by back-to-back diodes. If the differentia input votage exceeds.4, the input current shoud be imited to ess than ma. TYPICAL PERFORMANCE CHARACTERISTICS GAIN (db) OUTPUT IMPEDANCE (Ω) k Ampitude Response Passband Gain and Group Deay Passband Gain and Group Deay S = ±. R IN = 8Ω GAIN = M M M FREQUENCY (Hz) G GAIN (db) S = R IN = 8Ω 8 GAIN = T A = C FREQUENCY (MHz) G Output Impedance vs Frequency (OUT or OUT ) CMRR PSRR. k M M M FREQUENCY (Hz) G4 CMRR (db) k IN = P-P S = R IN = 8Ω GAIN = 8 4 GROUP DELAY (ns) k k M M M FREQUENCY (Hz) G GAIN (db) S = R IN = 4Ω GAIN = 4 T A = C FREQUENCY (MHz) PSRR (db) k G 8 4 TO DIFFERENTIAL OUT S = GROUP DELAY (ns) k k M M M FREQUENCY (Hz) G 4 fe

5 TYPICAL PERFORMANCE CHARACTERISTICS LT-. DISTORTION (db) Distortion vs Frequency DIFFERENTIAL INPUT, ND HARMONIC DIFFERENTIAL INPUT, RD HARMONIC SINGLE-ENDED INPUT, ND HARMONIC SINGLE-ENDED INPUT, RD HARMONIC DISTORTION (db) Distortion vs Frequency DIFFERENTIAL INPUT, ND HARMONIC DIFFERENTIAL INPUT, RD HARMONIC SINGLE-ENDED INPUT, ND HARMONIC SINGLE-ENDED INPUT, RD HARMONIC. IN = P-P S = R L = 8Ω AT EACH OUTPUT FREQUENCY (MHz). IN = P-P S = R L = 8Ω AT EACH OUTPUT FREQUENCY (MHz) G7 G8 DISTORTION (db) Distortion vs Frequency DIFFERENTIAL INPUT, ND HARMONIC DIFFERENTIAL INPUT, RD HARMONIC SINGLE-ENDED INPUT, ND HARMONIC SINGLE-ENDED INPUT, RD HARMONIC IN = P-P S = ± R L = 8Ω AT EACH OUTPUT FREQUENCY (MHz) G9 DISTORTION (db) Distortion vs Signa Leve ND HARMONIC, DIFFERENTIAL INPUT RD HARMONIC, DIFFERENTIAL INPUT ND HARMONIC, SINGLE-ENDED INPUT RD HARMONIC, SINGLE-ENDED INPUT S = F = MHz R L = 8Ω AT EACH OUTPUT 4 INPUT LEEL ( P-P ) G DISTORTION (db) Distortion vs Signa Leve ND HARMONIC, DIFFERENTIAL INPUT RD HARMONIC, DIFFERENTIAL INPUT ND HARMONIC, SINGLE-ENDED INPUT RD HARMONIC, SINGLE-ENDED INPUT S = F = MHz R L = 8Ω AT EACH OUTPUT INPUT LEEL ( P-P ) G DISTORTION (db) Distortion vs Signa Leve ND HARMONIC, DIFFERENTIAL INPUT RD HARMONIC, DIFFERENTIAL INPUT ND HARMONIC, SINGLE-ENDED INPUT RD HARMONIC, SINGLE-ENDED INPUT S = ± F = MHz R L = 8Ω AT EACH OUTPUT INPUT LEEL ( P-P ) G fe

6 LT-. TYPICAL PERFORMANCE CHARACTERISTICS DISTORTION COMPONENT (db) Distortion vs Input Common Mode Leve ND HARMONIC, S = RD HARMONIC, S = ND HARMONIC, S = RD HARMONIC, S = P-P MHz INPUT R IN = 8Ω GAIN = INPUT COMMON MODE OLTAGE RELATIE TO MID () G DISTORTION COMPONENT (db) Distortion vs Input Common Mode Leve ND HARMONIC, S = RD HARMONIC, S = ND HARMONIC, S = RD HARMONIC, S = P-P MHz INPUT, R IN = 4Ω, GAIN = 4 INPUT COMMON MODE OLTAGE RELATIE TO MID () G4 DISTORTION COMPONENT (db) Distortion vs Output Common Mode Leve ND HARMONIC, S = RD HARMONIC, S = ND HARMONIC, S = RD HARMONIC, S = ND HARMONIC, S = ± RD HARMONIC, S = ± TOTAL SUPPLY CURRENT (ma) Suppy Current vs Tota Suppy otage T A = 8 C T A = C T A = 4 C P-P MHz INPUT, R IN = 8Ω, GAIN = OLTAGE OCM TO MID () TOTAL SUPPLY OLTAGE () G G Transient Response Gain = OUT m/di DIFFERENTIAL INPUT m/di ns/di G7 fe

7 PIN FUNCTIONS (DFN/SO) IN and IN (Pins, /Pins, 8): Input Pins. Signas can be appied to either or both input pins through identica externa resistors, R IN. The DC gain from differentia inputs to the differentia outputs is 8Ω/R IN. NC (Pins,, /NA): No Connection OCM (Pin /Pin ): DC Common Mode Reference otagefor the nd Fiter Stage. Its vaue programs the common mode votage of the differentia output of the fiter. This is a high impedance input, which can be driven from an externa votage reference, or it can be tied to MID on the PC board. OCM shoud be bypassed with a.μf ceramic capacitor uness it is connected to a ground pane. and (Pins 4, 8, 9/Pins, ): Power Suppy Pins. For a singe. or suppy ( grounded) a quaity.μf ceramic bypass capacitor is required from the positive suppy pin ( ) to the negative suppy pin ( ). The bypass LT-. shoud be as cose as possibe to the IC. For dua suppy appications, bypass to ground and to ground with a quaity.μf ceramic capacitor. OUT and OUT (Pins, 7/Pins 4, ): Output Pins. These are the fiter differentia outputs. Each pin can drive a Ω and/or pf oad to AC ground. MID (Pin /Pin 7): The MID pin is internay biased at mid-suppy, see Bock Diagram. For singe suppy operation, the MID pin shoud be bypassed with a quaity.μf ceramic capacitor to. For dua suppy operation, MID can be bypassed or connected to a high quaity DC ground. A ground pane shoud be used. A poor ground wi increase noise and distortion. MID sets the output common mode votage of the st stage of the fiter. It has a.kω impedance, and it can be overridden with an externa ow impedance votage source. BLOCK DIAGRAM IN R IN IN MID OUT 8Ω OCM OP AMP k k 8Ω 8Ω OCM PROPRIETARY LOWPASS FILTER STAGE 8Ω 8Ω 8Ω IN R IN IN OCM OUT BD fe 7

8 LT-. APPLICATIONS INFORMATION Interfacing to the LT-. Note: The referenced pin numbers correspond to the S8 package. See the Pin Functions for the equivaent DFN- package pin numbers. The LT-. requires two equa externa resistors, R IN, to set the differentia gain to 8Ω/R IN. The inputs to the fiter are the votages IN and IN presented to the see externa components, Figure. The difference between IN and IN is the differentia input votage. The average of IN and IN is the common mode input votage. Simiary, the votages OUT and OUT appearing at Pins 4 and of the LT-. are the fiter outputs. The difference between OUT and OUT is the differentia output votage. The average of OUT and OUT is the common mode output votage. Figure iustrates the LT-. operating with a singe. suppy and unity passband gain; the input signa is DC-couped. The common mode input votage is., and the differentia input votage is P-P. The common mode output votage is., and the differentia output votage is P-P for frequencies beow.mhz. The common mode output votage is determined by the votage at OCM. Since OCM is shorted to MID, the output common mode is the mid-suppy votage. In addition, the common mode input votage can be equa to the mid-suppy votage of MID. Figure shows how to AC coupe signas into the LT-.. In this instance, the input is a singe-ended signa. AC-couping aows the processing of singe-ended or differentia signas with arbitrary common mode eves. The.μF couping capacitor and the 8Ω gain setting resistor form a highpass fi ter, attenuating signas beow khz. Larger vaues of couping capacitors wi proportionay reduce this highpass db frequency. In Figure the LT-. is providing db of gain. The common mode output votage is set to...μf 8Ω IN 4 7 OUT LT-. IN.μF 8 IN OUT 8Ω t IN Figure. (S8 Pin Numbers) OUT OUT F t IN t IN.μF 8Ω.μF.μF 8Ω..μF 4 7 LT-. 8 OUT OUT OUT OUT F t Figure. (S8 Pin Numbers) m P-P (DIFF) IN IN t IN IN 4Ω 4Ω.μF.μF 4 7 LT-. 8 OUT OUT OUT OUT F t 8 Figure. (S8 Pin Numbers) fe

9 APPLICATIONS INFORMATION Use Figure 4 to determine the interface between the LT-. and a current output DAC. The gain, or transimpedance, is defined as A = OUT /I IN. To compute the transimpedance, use the foowing equation: 8 R A = RR ( ) ( Ω) By setting R R = 8Ω, the gain equation reduces to A = R(Ω). The votage at the pins of the DAC is determined by R, R, the votage on MID and the DAC output current. Consider Figure 4 with R = 49.9Ω and R = 4Ω. The votage at MID, for S =., is.. The votage at the DAC pins is given by: R DAC = PIN7 RR 8 I IN R R RR = m I IN 48.Ω I IN is I IN or I IN. The transimpedance in this exampe is 49.Ω. Evauating the LT-. The ow impedance eves and high frequency operation of the LT-. require some attention to the matching networks between the LT-. and other devices. The previous exampes assume an idea (Ω) source impedance and a arge (kω) oad resistance. Among practica exampes where impedance must be considered is the evauation of the LT-. with a network anayzer. LT-. Figure is a aboratory setup that can be used to characterize the LT-. using singe-ended instruments with Ω source impedance and Ω input impedance. For a db gain configuration the LT-. requires a 4Ω source resistance yet the network anayzer output is caibrated for a Ω oad resistance. The : transformer,.ω and 88Ω resistors satisfy the two constraints above. The transformer converts the singe-ended source into a differentia stimuus. Simiary, the output of the LT-. wi have ower distortion with arger oad resistance yet the anayzer input is typicay Ω. The 4: turns (: impedance) transformer and the two 4Ω resistors of Figure, present the output of the LT-. with a Ω differentia oad, or the equivaent of 8Ω to ground at each output. The impedance seen by the network anayzer input is sti Ω, reducing refections in the cabing between the transformer and anayzer input. Differentia and Common Mode otage Ranges The rai-to-rai output stage of the LT-. can process arge differentia signa eves. On a suppy, the output signa can be. P-P. Simiary, a suppy can support signas as arge as 8.8 P-P. To prevent excessive power dissipation in the interna circuitry, the user must imit differentia signa eves to 9 P-P. The two ampifiers inside the LT-. have independent contro of their output common mode votage (see the Bock Diagram section). The foowing guideines wi optimize the performance of the fiter. CURRENT OUTPUT DAC I IN R I IN R.μF R R 7 8 F4..μF 4 LT-. OUT OUT OUT OUT I IN IIN 8 R = R R NETWORK ANALYZER SOURCE Ω COILCRAFT TTWB- : 88Ω 7.Ω 8 88Ω..μF LT-. 4.μF. COILCRAFT TTWB-A 4: 4Ω 4Ω NETWORK ANALYZER INPUT Ω F Figure 4. (S8 Pin Numbers) Figure. (S8 Pin Numbers) fe 9

10 LT-. APPLICATIONS INFORMATION MID can be aowed to foat, but it must be bypassed to an AC ground with a.μf capacitor or some instabiity maybe observed. MID can be driven from a ow impedance source, provided it remains at east. above and at east. beow. An interna resistor divider sets the votage of MID. Whie the interna k resistors are we matched, their absoute vaue can vary by ±%. This shoud be taken into consideration when connecting an externa resistor network to ater the votage of MID. OCM can be shorted to MID for simpicity. If a different common mode output votage is required, connect OCM to a votage source or resistor network. For and. suppies the votage at OCM must be ess than or equa to the mid-suppy eve. For exampe, votage ( OCM ). on a singe. suppy. For power suppy votages higher than. the votage at OCM can be set above mid-suppy, as shown in Tabe. The votage on OCM shoud not exceed beow the votage on MID. OCM is a high impedance input. Tabe. Output Common Range for arious Suppies SUPPLY OLTAGE DIFFERENTIAL OUT OLTAGE SWING OUTPUT COMMON MODE RANGE FOR LOW DISTORTION 4 P-P.4 OCM. P-P OCM. P-P.7 OCM. 8 P-P.4 OCM. 4 P-P. OCM. P-P OCM.7 P-P.7 OCM.7 ± 9 P-P OCM 4 P-P. OCM. P-P.7 OCM.7 P-P 4. OCM.7 NOTE: OCM is set by the votage at this R IN. The votage at OCM shoud not exceed beow the votage at MID. To achieve some of the output common mode ranges shown in the tabe, the votage at MID must be set externay to a vaue beow mid suppy. The LT-. was designed to process a variety of input signas incuding signas centered around the mid-suppy votage and signas that swing between ground and a positive votage in a singe suppy system (Figure ). The range of aowabe input common mode votage (the average of IN and IN in Figure ) is determined by the power suppy eve and gain setting (see Eectrica Characteristics). Common Mode DC Currents In appications ike Figure and Figure where the LT-. not ony provides owpass fi tering but aso eve shifts the common mode votage of the input signa, DC currents wi be generated through the DC path between input and output terminas. Minimize these currents to decrease power dissipation and distortion. Consider the appication in Figure. MID sets the output common mode votage of the st differentia ampifi er inside the LT-. (see the Bock Diagram section) at.. Since the input common mode votage is near, there wi be approximatey a tota of. drop across the series combination of the interna 8Ω feedback resistor and the externa 4Ω input resistor. The resuting.ma common mode DC current in each input path,must be absorbed by the sources IN and IN. OCM sets the common mode output votage of the nd differentia ampifier inside the LT-., and therefore sets the common mode output votage of the fiter. Since, in the exampe of Figure, OCM differs from MID by., an additiona μa (μa per side) of DC current wi fow in the resistors couping the st differentia ampifier output stage to fiter output. Thus, a tota of.ma is used to transate the common mode votages. A simpe modification to Figure wi reduce the DC common mode currents by %. If MID is shorted to OCM the common mode output votage of both op amp stages wi be and the resuting DC current wi be ma. Of course, by AC-couping the inputs of Figure, the common mode DC current can be reduced to μa. fe

11 APPLICATIONS INFORMATION Noise The noise performance of the LT-. can be evauated with the circuit of Figure. Given the ow noise output of the LT-. and the db attenuation of the transformer couping network, it wi be necessary to measure the noise foor of the spectrum anayzer and subtract the instrument noise from the fiter noise measurement. IN R IN R IN..μF 4 7 LT-. 8.μF. Ω Ω Figure. (S8 Pin Numbers) COILCRAFT TTWB- : SPECTRUM ANALYZER INPUT F Exampe: With the IC removed and the Ω resistorsgrounded, Figure, measure the tota integrated noise (e S ) of the spectrum anayzer from khz to.mhz. With the IC inserted, the signa source ( IN ) disconnected, and the input resistors grounded, measure the tota integrated noise out of the fiter (e O ). With the signa source connected, set the frequency to khz and adjust the ampitude unti IN measures m P-P. Measure the output ampitude, OUT, and compute the passband gain A = OUT / IN. Now compute the input referred integrated noise (e IN ) as: e IN = (e O ) (e S ) A Tabe ists the typica input referred integrated noise for various vaues of R IN. Tabe. Noise Performance PASSBAND GAIN (/) R IN INPUT REFERRED INTEGRATED NOISE khz TO.MHz INPUT REFERRED INTEGRATED NOISE khz TO MHz 4 4Ω 8μ RMS μ RMS 8Ω 9μ RMS 9μ RMS 8Ω μ RMS 7μ RMS Ω NOISE SPECTRAL DENSITY (n RMS / Hz) 4. SPECTRAL DENSITY. FREQUENCY (MHz) Figure 7. Input Referred Noise, Gain = LT-. INTEGRATED F7 Figure 7 is pot of the noise spectra density as a function of frequency for an LT-. with R IN = 8Ω using the fixture of Figure (the instrument noise has been subtracted from the resuts). The noise at each output is comprised of a differentia component and a common mode component. Using a transformer or combiner to convert the differentia outputs to singe-ended signa rejects the common mode noise and gives a true measure of the S/N achievabe in the system. Conversey, if each output is measured individuay and the noise power added together, the resuting cacuated noise eve wi be higher than the true differentia noise. Power Dissipation The LT-. ampifiers combine high speed with argesigna currents in a sma package. There is a need to ensure that the die s junction temperature does not exceed C. The LT-. S8 package has Pin fused to the ead frame to enhance therma conduction when connecting to a ground pane or a arge meta trace. Meta trace and pated through-hoes can be used to spread the heat generated by the device to the backside of the PC board. For exampe, on a /" FR-4 board with oz copper, a totaof square miimeters connected to Pin of the LT-. S8 ( square miimeters on each side of the PC board) wi resut in a therma resistance, θ JA, of about 8 C/W. Without the extra meta trace connected to 8 4 INTEGRATED NOISE (μ RMS ) fe

12 LT-. APPLICATIONS INFORMATION the pin to provide a heat sink, the therma resistance wi be around C/W. Tabe can be used as a guide when considering therma resistance. Tabe. LT-. SO-8 Package Therma Resistance COPPER AREA TOPSIDE (mm ) BACKSIDE (mm ) BOARD AREA (mm ) THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) C/W 8 C/W 9 C/W C/W C/W Junction temperature, T J, is cacuated from the ambienttemperature, T A, and power dissipation, P D. The power dissipation is the product of suppy votage, S, and suppy current, I S. Therefore, the junction temperature is given by: T J = T A (P D θ JA ) = T A ( S I S θ JA ) where the suppy current, I S, is a function of signa eve, oad impedance, temperature and common mode votages. For a given suppy votage, the worst-case power dissipation occurs when the differentia input signa is maximum, the common mode currents are maximum (see Appications Information regarding Common Mode DC Currents), the oad impedance is sma and the ambient temperature is maximum. To compute the junction temperature, measure the suppy current under these worst-case conditions, estimate the therma resistance from Tabe, then appy the equation for T J. For exampe, using the circuit in Figure with DC differentia input votage of, a differentia output votage of 4, no oad resistance and an ambient temperature of 8 C, the suppy current (current into ) measures 7.mA. Assuming a PC board ayout with a mm copper trace, the θ JA is C/W. The resuting junction temperature is: T J = T A (P D θ JA ) = 8 (.7 ) = 4 C When using higher suppy votages or when driving sma impedances, more copper may be necessary to keep T J beow C. fe

13 PACKAGE DESCRIPTION DF Package -Lead Pastic DFN (4mm 4mm) (Reference LTC DWG # -8-7 Rev Ø) LT-.. REF.7 ±. 4. ±.. ±..8 ±.. ±. PACKAGE OUTLINE. ±.. BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4. ±. (4 SIDES) 7. REF.4 ±..8 ±.. ±. PIN TOP MARK (NOTE ) PIN NOTCH R =. TYP OR. 4 CHAMFER. REF.7 ±. R =. TYP BOTTOM IEW EXPOSED PAD. ±.. BSC (DF) DFN 8 RE Ø.. NOTE:. DRAWING IS PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO- ARIATION (WGGD-X) TO BE APPROED. DRAWING NOT TO SCALE. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED.mm ON ANY SIDE. EXPOSED PAD SHALL BE SOLDER PLATED. SHADED AREA IS ONLY A REFERENCE FOR PIN LOCATION ON THE TOP AND BOTTOM OF PACKAGE fe

14 LT-. PACKAGE DESCRIPTION S8 Package 8-Lead Pastic Sma Outine (Narrow. Inch) (Reference LTC DWG # -8-). BSC.4 ± (4.8.4) NOTE MIN. ± (.79.97)..7 (.8.988) NOTE. ±. TYP RECOMMENDED SOLDER PAD LAYOUT 4.8. (..4).. (.4.8) 4 8 TYP..9 (.4.7).4. (..4).. (.4.7) NOTE: INCHES. DIMENSIONS IN (MILLIMETERS).4.9 (..48) TYP. DRAWING NOT TO SCALE. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED." (.mm). (.7) BSC SO8 4 fe

15 LT-. REISION HISTORY (Revision history begins at Rev E) RE DATE DESCRIPTION PAGE NUMBER E / Updated Order Information section Information furnished by Linear Technoogy Corporation is beieved to be accurate and reiabe. However, no responsibiity is assumed for its use. Linear Technoogy Corporation makes no representation that the interconnection of its circuits as described herein wi not infringe on existing patent rights. fe

16 LT-. TYPICAL APPLICATION th Order Lowpass Fiter (S8 Pin Numbers Shown).μF C = IN IN R R π R.MHz C R R 7 8 8Ω GAIN =, MAXIMUM GAIN = 4 R LT 4.μF OUT OUT TAa GAIN (db) k Ampitude Response Transient Response Gain = M FREQUENCY (Hz) S = ±. GAIN = R = 787Ω T A = C M M TAb OUT m/di DIFFERENTIAL INPUT m/di ns/di TAc RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC - khz Linear Phase Lowpass Fiter Continuous Time, SO8 Package, Fuy Differentia LTC- Low Noise,.MHz Lowpass Fiter Continuous Time, SO8 Package LT7 ery Low Noise, High Frequency Fiter Buiding Bock.4n/ Hz Op Amp, MSOP Package, Fuy Differentia LT8 ery Low Noise, 4th Order Buiding Bock Lowpass and Bandpass Fiter Designs Up to MHz, Differentia Outputs LTC99 Low-Power Differentia In/Out Ampifi er Adjustabe Gain, MSOP Package LTC99- Low-Power Differentia In/Out Ampifi er Fixed Gain of, Matching ±.% LTC99- Low-Power Differentia In/Out Ampifi er Fixed Gain of, Matching ±.% LTC99- Low-Power Differentia In/Out Ampifi er Fixed Gain of, Matching ±.% LTC99- Low-Power Differentia In/Out Ampifi er Fixed Gain of, Matching ±.% LT- ery Low Noise Differentia Ampifi er and MHz 8dB S/N with Suppy, SO-8 Package Lowpass Fiter LT- ery Low Noise Differentia Ampifi er and MHz Lowpass Fiter 7dB S/N with Suppy, SO-8 Package fe LT RE E PRINTED IN USA Linear Technoogy Corporation McCarthy Bvd., Mipitas, CA (48) 4-9 FAX: (48) LINEAR TECHNOLOGY CORPORATION

17 Mouser Eectronics Authorized Distributor Cick to iew Pricing, Inventory, Deivery & Lifecyce Information: Anaog Devices Inc.: LTCS8-. LTIS8-. LTCS8-.#PBF LTIS8-.#PBF LTIS8-.#TR LTCS8-.#TR LTIDF-.#PBF LTCDF-.#PBF LTCDF-.#TRPBF LTCS8-.#TRPBF LTIS8-.#TRPBF LTIDF-.#TRPBF