LT Dual Very Low Noise, Differential Amplifi er and 15MHz Lowpass Filter DESCRIPTION FEATURES APPLICATIONS TYPICAL APPLICATION

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1 FEATURES n Dua Differentia Ampifi er with MHz Lowpass Fiters th Order Fiters Approximates Chebyshev Response Guaranteed Phase and Gain Matching Resistor-Programmabe Differentia Gain n 7 Signa-to-Noise ( Suppy, P-P Output) n Low Distortion, P-P, 8Ω Load, S = MHz: 8c nd, 9c rd MHz: c nd, 9c rd n Specifi ed for Operation with, and ± Suppies n Fuy Differentia Inputs and Outputs n Adjustabe Output Common Mode otage n Sma mm 7mm.7mm QFN Package APPLICATIONS n Dua Differentia ADC Driver Pus Fiter n Singe-Ended to Differentia Converter n Matched, Dua, Differentia Fiter Stage n Common Mode Transation of Differentia Signas n High Speed ADC Antiaiasing and DAC Smoothing in Wireess Infrastructure or Networking Appications n High Speed Test and Measurement Equipment n Medica Imaging LT- Dua ery Low Noise, Differentia Ampifi er and MHz Lowpass Fiter DESCRIPTION The LT - consists of two matched, fuy differentia ampifi ers, each with a th order, MHz owpass fiter. The fi xed frequency owpass fiter approximates a Chebyshev response. By integrating a fi ter and a differentia ampifi er, distortion and noise are made exceptionay ow. At unity gain, the measured in band signa-to-noise ratio is an impressive 7. At higher gains, the input referred noise decreases, aowing the part to process smaer input differentia signas without signifi canty degrading the signa-to-noise ratio. Gain and phase are highy matched between the two channes. Gain for each channe is independenty programmed using two externa resistors. The LT- enabes eve shifting by providing an adjustabe output common mode votage, making it idea for directy interfacing to ADCs. The LT- is fuy specifi ed for operation. The differentia design enabes outstanding performance at a P-P signa eve for a singe suppy. See the back page of this datasheet for a compete ist of reated singe and dua differentia ampifi ers with integrated.mhz to MHz owpass fiters. L, LT, LTC and LTM are registered trademarks of Linear Technoogy Corporation. A other trademarks are the property of their respective owners. TYPICAL APPLICATION.μF.μF LT- INA MIDA OCMA INA INB MIDB OCMB INB A OUTA OUTA B OUTB OUTB Ω Ω Ω Ω 8pF 8pF LTCxx AIN AIN DUAL ADC DOUT DOUT TA Channe to Channe Gain Matching 8 TYPICAL UNITS T A = C GAIN = f IN = MHz GAIN MATCH () TAb fb

2 LT- ABSOLUTE MAXIMUM RATINGS (Note ) Tota Suppy otage... Operating Temperature Range (Note )... C to 8 C Specifi ed Temperature Range (Note 7)... C to 8 C Junction Temperature... C Storage Temperature Range... C to C Input Current IN, IN, OCM, MID (Note 8)...±mA Lead Temperature (Sodering, sec)... C PIN CONFIGURATION TOP IEW MIDA INA INA OCMA 7 MIDB 8 9 INB INB 9 OUTA 8 7 OUTA A OUTB 9 OUTB 8 OCMB B 7 UFF PACKAGE -LEAD (mm 7mm) PLASTIC QFN T JMAX = C, θ JA = C/W, θ JC =.7 C/W EXPOSED PAD (PIN ) IS, MUST BE SOLDERED TO PCB ORDEFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LTCUFF-#PBF LTCUFF-#TRPBF -Lead (mm 7mm) Pastic QFN C to 7 C LTIUFF-#PBF LTIUFF-#TRPBF -Lead (mm 7mm) Pastic QFN 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. Consut LTC Marketing for information on non-standard 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 specifi cations that appy over the fu operating temperature range, otherwise specifi cations are at T A = C. Uness otherwise specifi ed S = ( =, = ), =, and R LOAD = k. PARAMETER CONDITIONS MIN TYP MAX UNITS Fiter Gain Either Channe, S = IN = P-P, f IN = DC to khz... IN = P-P, f IN =.MHz (Gain Reative to khz) IN = P-P, f IN = 7.MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = 7MHz (Gain Reative to khz) fb

3 LT- ELECTRICAL CHARACTERISTICS The denotes specifi cations that appy over the fu operating temperature range, otherwise specifi cations are at T A = C. Uness otherwise specifi ed S = ( =, = ), =, and R LOAD = k. PARAMETER CONDITIONS MIN TYP MAX UNITS Matching of Fiter Gain, S = IN = P-P, f IN = DC to khz.. IN = P-P, f IN =.MHz (Gain Reative to khz) IN = P-P, f IN = 7.MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = 7MHz (Gain Reative to khz) Matching of Fiter Phase, S = Fiter Gain Either Channe, S = Matching of Fiter Gain, S = Matching of Fiter Phase, S = IN = P-P, f IN =.MHz IN = P-P, f IN = 7.MHz IN = P-P, f IN = MHz IN = P-P, f IN = DC to khz IN = P-P, f IN =.MHz (Gain Reative to khz) IN = P-P, f IN = 7.MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = 7MHz (Gain Reative to khz) IN = P-P, f IN = DC to khz IN = P-P, f IN =.MHz (Gain Reative to khz) IN = P-P, f IN = 7.MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = MHz (Gain Reative to khz) IN = P-P, f IN = 7MHz (Gain Reative to khz) IN = P-P, f IN =.MHz IN = P-P, f IN = 7.MHz IN = P-P, f IN = MHz Fiter Gain Either Channe, S = ± IN = P-P, f IN = DC to khz... Fiter Gain, = Ω IN =. P-P, f IN = DC to khz S = S = S = ± Fiter Gain Temperature Coeffi cient (Note ) f IN = khz, IN = P-P 78 ppm/ C Noise Noise BW = khz to MHz, = 9 μ RMS Distortion (Note ) MHz, P-P, R L = 8Ω, S = nd Harmonic rd Harmonic MHz, P-P, R L = 8Ω, S = nd Harmonic rd Harmonic Channe Separation (Note 9) MHz, P-P, R L = 8Ω 7 MHz, P-P, R L = 8Ω Differentia Output Swing Measured Between OUT and OUT, OCM shorted to MID S = S = P-P_DIFF P-P_DIFF Input Bias Current Average of IN and IN 9 μa Input Referred Differentia Offset = S = S = S = ± = Ω S = S = S = ± deg deg deg deg deg deg c c c c m m m m m m fb

4 LT- ELECTRICAL CHARACTERISTICS The denotes specifi cations that appy over the fu operating temperature range, otherwise specifi cations are at T A = C. Uness otherwise specifi ed S = ( =, = ), =, and R LOAD = k. PARAMETER CONDITIONS MIN TYP MAX UNITS Differentia Offset Drift μ/ C Input Common Mode otage (Note ) Differentia Input = m P-P, = Ω S = S = S = ± Output Common Mode otage (Note ) Differentia Output = P-P, MID = Open, Common Mode otage at OCM S = S = S = ± Output Common Mode Offset (with Respect to OCM ) S = S = S = ± Common Mode Rejection Ratio otage at MID S = S =.... MID Input Resistance kω OCM Bias Current OCM = MID = S / S = S = Power Suppy Current (per Channe) S =, S = S = S = S = ± Power Suppy otage m m m μa μa ma ma ma ma 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 ( ). Note : The input common mode votage is the average of the votages appied to the externa resistors ( ). Specifi cation guaranteed for Ω. Note : Distortion is measured differentiay using a differentia 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 OUT and OUT votages. The output common mode votage is equa to OCM. Note : The LTC- is guaranteed functiona over the operating temperature range C to 8 C. Note 7: The LTC- is guaranteed to meet C to 7 C specifi cations and is designed, characterized and expected to meet the extended temperature imits, but is not tested at C and 8 C. The LTI- is guaranteed to meet specifi ed performance from C to 8 C. Note 8: Input pins (IN, IN, OCM and MID ) are protected by steering diodes to either suppy. If the inputs shoud exceed either suppy votage, the input current shoud be imited to ess than ma. In addition, the inputs IN, IN are protected by a pair of back-to-back diodes. If the differentia input votage exceeds., the input current shoud be imited to ess than ma. Note 9: Channe separation (the inverse of crosstak) is measured by driving a signa into one input, whie terminating the other input. Channe separation is the ratio of the resuting output signa at the driven channe to the output at the channe that is not driven. fb

5 TYPICAL PERFORMAE CHARACTERISTICS LT- GAIN () Ampitude Response S = GAIN = T A = C. FREQUEY (MHz) G GAIN () Passband Gain and Phase GAIN PHASE S = GAIN = T A = C FREQUEY (MHz) G PHASE (DEG) GAIN () Passband Gain and Deay DELAY GAIN S = GAIN = T A = C FREQUEY (MHz) G DELAY (ns) GAIN () 8 Passband Gain and Deay GAIN DELAY S = GAIN = T A = C DELAY (ns) OUTPUT IMPEDAE (Ω) Output Impedance S = GAIN = T A = C CMRR () Common Mode Rejection Ratio IN = P-P S = GAIN = T A = C FREQUEY (MHz).. FREQUEY (MHz). FREQUEY (MHz) G G G PSRR () 8 7. Power Suppy Rejection Ratio Distortion vs Frequency Distortion vs Signa Leve S = IN = m P-P T A = C TO DIFFOUT FREQUEY (MHz) G7 DISTORTION (c) IN = P-P S = R L = 8Ω AT EACH OUTPUT GAIN = T A = C FREQUEY (MHz) G8 DIFFERENTIAL INPUT, ND HARMONIC DIFFERENTIAL INPUT, RD HARMONIC SINGLE-ENDED INPUT, ND HARMONIC SINGLE-ENDED INPUT, RD HARMONIC DISTORTION (c) S = R L = 8Ω AT EACH OUTPUT GAIN = T A = C ND HARMONIC MHz INPUT RD HARMONIC MHz INPUT ND HARMONIC MHz INPUT RD HARMONIC MHz INPUT INPUT LEEL ( P-P ) G9 fb

6 LT- TYPICAL PERFORMAE CHARACTERISTICS DISTORTION (c) Distortion vs Signa Leve S = ± R L = 8Ω AT EACH OUTPUT GAIN = T A = C ND HARMONIC, MHz INPUT RD HARMONIC, MHz INPUT ND HARMONIC, MHz INPUT RD HARMONIC, MHz INPUT INPUT LEEL ( P-P ) G DISTORTION COMPONENT (c) Distortion vs Input Common Mode Leve ND HARMONIC, S = RD HARMONIC, S = ND HARMONIC, S = RD HARMONIC, S = GAIN = R L = 8Ω AT EACH OUTPUT T A = C P-P MHz INPUT INPUT COMMON MODE OTLAGE RELATIE TO MID () G DISTORTION COMPONENT (c) 7 8 Distortion vs Input Common Mode Leve ND HARMONIC, S = RD HARMONIC, S = ND HARMONIC, S = RD HARMONIC, S = 9 GAIN =, R L = 8Ω AT EACH OUTPUT T A = C, m P-P MHz INPUT INPUT COMMON MODE OTLAGE RELATIE TO MID () G DISTORTION COMPONENT (c) Distortion vs Output Common Mode Leve ND HARMONIC, S = RD HARMONIC, S = ND HARMONIC, S = RD HARMONIC, 7 S = ND HARMONIC, 8 S = ± RD HARMONIC, 9 S = ± P-P MHz INPUT GAIN =, R L = 8Ω AT EACH OUTPUT T A = C..... ( OCM MID ) OLTAGE () G SUPPLY CURRENT (ma) Singe Channe Suppy Current vs Tota Suppy otage T A = 8 C T A = C T A = C 8 TOTAL SUPPLY OLTAGE () G OUT m/di OUT m/di IN IN m/di Transient Response, ns/di DIFFERENTIAL GAIN = SINGLE-ENDED INPUT DIFFERENTAL OUTPUT G CHANNEL SEPARATION () Channe Separation vs Frequency (Note 9) IN = P-P S = R L = 8Ω AT EACH OUTPUT GAIN = FREQUEY (MHz) G fb

7 PIN FUTIONS INA and INA (Pins, ): Channe A Input Pins. Signas can be appied to either or both input pins through identica externa resistors,. The DC gain from differentia inputs to the differentia outputs is /. OCMA (Pin ): DC Common Mode Reference otage for the nd Fiter Stage in Channe A. Its vaue programs the common mode votage of the differentia output of the fi ter. Pin is a high impedance input, which can be driven from an externa votage reference, or Pin can be tied to Pin on the PC board. Pin shoud be bypassed with a.μf ceramic capacitor uness it is connected to a ground pane. (Pins 7,,,, ): Negative Power Suppy Pin (can be ground). MIDB (Pin 8): The MIDB pin is internay biased at midsuppy, see Bock Diagram. For singe suppy operation the MIDB pin shoud be bypassed with a quaity.μf ceramic capacitor to ground. For dua suppy operation, Pin 8 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. Pin 8 sets the output common mode votage of the st Fiter Stage in channe B. It has a.kω impedance, and it can be overridden with an externa ow impedance votage source. INB and INB(Pins, ): Channe B Input Pins. Signas can be appied to either or both input pins through identica externa resistors,. The DC gain from differentia inputs to the differentia outputs is /. OCMB (Pin ): Is the DC Common Mode Reference otage for the nd Fiter Stage in Channe B. Its vaue programs the common mode votage of the differentia output of the fiter. Pin is a high impedance input, which can be driven from an externa votage reference, or Pin LT- can be tied to Pin 8 on the PC board. Pin shoud be bypassed with a.μf ceramic capacitor uness it is connected to a ground pane. A and B (Pins, 7): Positive Power Suppy Pins for Channes A and B. For a singe. or suppy (Pins 7,,, and grounded) a quaity.μf ceramic bypass capacitor is required from the positive suppy pin (Pins, 7) to the negative suppy pin (Pins 7,,, and ). The bypass shoud be as cose as possibe to the IC. For dua suppy appications, bypass the negative suppy pins to ground and Pins and 7 to ground with a quaity.μf ceramic capacitor. OUTB and OUTB(Pins 9, ): Output Pins. Pins 9 and are the fi ter differentia outputs for channe B. With a typica short-circuit current imit greater than ±ma each pin can drive a Ω and/or pf oad to AC ground. OUTA and OUTA (Pins 7, 9): Output Pins. Pins 7 and 9 are the fi ter differentia outputs for channe A. With a typica short-circuit current imit greater than ±ma each pin can drive a Ω and/or pf oad to AC ground. MIDA (Pin ): The MIDA pin is internay biased at midsuppy, see Bock Diagram. For singe suppy operation the MIDA pin shoud be bypassed with a quaity.μf ceramic capacitor to ground. For dua suppy operation, Pin 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. Pin sets the output common mode votage of the st stage fiter stage in channe A. It has a.kω impedance, and it can be overridden with an externa ow impedance votage source. Exposed Pad (Pin ):. The Exposed Pad must be sodered to the PCB. fb 7

8 LT- BLOCK DIAGRAM MIDA A IN A INA k k PROPRIETARY LOWPASS FILTER STAGE Ω 9 8 OUTA IN A INA OCM OP AMP Ω Ω OCM 7 OUTA OCMA Ω A 7 B MIDB 8 k k PROPRIETARY LOWPASS FILTER STAGE IN B INB 9 OCM OP AMP Ω Ω OCM Ω OUTB IN B INB Ω 9 OUTB 7 OCMB B 8 BD 8 fb

9 APPLICATIONS INFORMATION Interfacing to the LT- Note: The LT- contains two identica fi ters. The foowing appications information ony refers to one fiter. The two fiters are independent except that they share the same negative suppy votage. The two fiters can be used simutaneousy by repicating the exampe circuits. The referenced pin numbers correspond to the A channe fiter The LT- channe requires two equa externa resistors,, to set the differentia gain to /. The inputs to the fiter are the votages IN and IN presented to these 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 7 and 9 of the LT- are the fi ter outputs. The difference between OUT and OUT is the differentia output votage. The average of OUT and OUT is the common LT- 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 gain setting resistor form a high pass fiter, attenuating signas beow khz. Larger vaues of couping capacitors wi proportionay reduce this highpass frequency...μf IN 7 / OUT LT- IN.μF IN 9 OUT t 7 IN OUT OUT F t Figure IN t IN.μF.μF.μF..μF 7 / LT- 7 9 OUT OUT OUT OUT F Figure fb 9

10 LT- APPLICATIONS INFORMATION In Figure the LT- is providing of gain. The gain resistor has an optiona pf in parae to improve the passband f atness near MHz. The common mode output votage is set to. Use Figure to determine the interface between the LT- and a current output DAC. The gain, or transimpedance, is defi ned as A = OUT /I IN. To compute the transimpedance, use the foowing equation: R A = (RR) (Ω) By setting R R =, 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 with R = 9.9Ω and R = 87Ω. The votage at MID, for S =., is.. The votage at the DAC pins is given by: R DAC = MID RR I IN R R RR =77m I IN.Ω I IN is I IN or I IN. The transimpedance in this exampe is 9.8Ω. 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 (k) oad resistance. Among practica exampes m P-P (DIFF) IN IN t IN IN pf Ω Ω.μF.μF 7 / LT- 7 9 OUT OUT OUT OUT F t pf Figure CURRENT OUTPUT DAC I IN I IN R R R.μF R..μF / LT OUT OUT NETWORK ANALYZER SOURCE Ω COILCRAFT TTWB- : Ω.Ω Ω..μF 7 / LT- 9 7.μF COILCRAFT TTWB-A : Ω Ω NETWORK ANALYZER INPUT Ω F OUT OUT = I IN IIN R R R F. Figure Figure fb

11 LT- APPLICATIONS INFORMATION where impedance must be considered is the evauation of the LT- with a network anayzer. 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 unity gain confi guration the LT- requires an source resistance yet the network anayzer output is caibrated for a Ω oad resistance. The : transformer,.ω and Ω resistors satisfy the two constraints above. The transformer converts the singeended 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 : turns (: impedance) transformer and the two Ω 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 ref ections in the cabing between the transformer and anayzer input. Differentia and Common Mode otage Ranges The differentia ampifi ers inside the LT- contain circuitry to imit the maximum peak-to-peak differentia votage through the fiter. This imiting function prevents excessive power dissipation in the interna circuitry and provides output short-circuit protection. The imiting function begins to take effect at output signa eves OUTPUT LEEL () 8 COMPRESSION POINTS RD HARMONIC C ND HARMONIC 8 C RD HARMONIC 8 C ND HARMONIC, C 8 C C 7 MHz INPUT LEEL ( P-P ) F above P-P and it becomes noticeabe above. P-P. This is iustrated in Figure ; the LT- channe was confi gured with unity passband gain and the input of the fiter was driven with a MHz signa. Because this votage imiting takes pace we before the output stage of the fiter reaches the suppy rais, the input/output behavior of the IC shown in Figure is reativey independent of the power suppy votage. The two ampifi ers inside the LT- channe have independent contro of their output common mode votage (see the Bock Diagram section). The foowing guideines wi optimize the performance of the fiter. MID can be aowed to f oat, but it must be bypassed to an AC ground with a.μf capacitor or some instabiity may be 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. The votage on OCM shoud not be more than beow the votage on MID. The votage on OCM shoud not be more than above the votage on MID. OCM is a high impedance input. The LT- was designed to process a variety of input signas incuding signas centered on 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 Distortion vs Input Common Mode Leve in the Typica Performance Characteristics). Figure. Output Leve vs Input Leve, Differentia MHz Input, Gain = fb

12 LT- APPLICATIONS INFORMATION 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- channe (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 feedback resistor and the externa Ω input resistor. The resuting.7ma 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 ampifi er inside the LT- channe, and therefore sets the common mode output votage of the fiter. Since, in the exampe of Figure, OCM differs from MID by., an additiona.ma (.ma per side) of DC current wi f ow in the resistors couping the st differentia ampifi er output stage to the fiter output. Thus, a tota of 9.9mA per channe is used to transate the common mode votages. A simpe modifi cation 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 per channe. Of course, by AC couping the inputs of Figure, the common mode DC current can be reduced to.ma per channe. Noise The noise performance of the LT- channe can be evauated with the circuit of Figure. Given the ow noise output of the LT- and the 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. Exampe: With the IC removed and the Ω resistors grounded, 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 MHz 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. Tabe. Noise Performance PASSBAND GAIN INPUT REFERRED INTEGRATED NOISE khz TO MHz INPUT REFERRED INTEGRATED NOISE khz TO MHz Ω μ RMS μ RMS 7Ω μ RMS 9μ RMS 9μ RMS 9μ RMS fb

13 APPLICATIONS INFORMATION Figure 8 is pot of the noise spectra density as a function of frequency for an LT- with = using the fi xture of Figure 7 (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- ampifi ers combine high speed with arge signa currents in a sma package. There is a need to ensure that the die s junction temperature does not exceed C. The LT- has an Exposed Pad (pin ) which is connected to the ower suppy ( ). Connecting the pad to a ground pane heps to dissipate the heat generated by the chip. Meta trace and pated through-hoes can be used to spread the heat generated by the device to the backside of the PC board. Junction temperature, T J, is cacuated from the ambient temperature, T A, and power dissipation, P D. The power dissipation is the product of suppy votage, S, and IN...μF 7 / LT- 9.μF 7 Ω Ω COILCRAFT TTWB- : SPECTRUM ANALYZER INPUT Ω F7 LT- 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 worstcase conditions, use C/W as the package therma resistance, then appy the equation for TJ. For exampe, using the circuit in Figure with DC differentia input votage of m, a differentia output votage of, no oad resistance and an ambient temperature of 8 C, the suppy current (current into ) measures ma The resuting junction temperature is: T J = T A (P D θ JA ) = 8 (. ) = C. The therma resistance can be affected by the amount of copper on the PCB that is connected to. The therma resistance of the circuit can increase if the exposed pad is not connected to a arge ground pane with a number of vias. NOISE DENSITY (n RMS / Hz) NOISE DENSITY, GAIN = x NOISE DENSITY, GAIN = x INTEGRATED NOISE, GAIN = x INTEGRATED NOISE, GAIN = x.. FREQUEY (MHz) F8 8 8 INTEGRATED NOISE (μ) Figure 7 Figure 8. Input Referred Noise, Gain = fb

14 LT- TYPICAL APPLICATION Dua Matched I and Q Lowpass Fiter and ADC (Typica Phase Matching ± Degree).μF CMA I.μF.μF 7 / LT- 7 9 Ω Ω.μF.pF.pF.pF INA LTC99 Q.μF 8.μF 9 / LT- 7 Ω Ω GAIN = /.pf.pf.pf CMB INB.μF TA fb

15 PACKAGE DESCRIPTION UFF Package -Lead Pastic QFN (mm 7mm) (Reference LTC DWG # Rev Ø) LT-.7 ±.. ±.. ±.. REF.9 ±..7 ±..8 ±..9 ±.. ±. PACKAGE OUTLINE.9 ±.. ±.. BSC. REF. ±. 7. ±. PIN TOP MARK (NOTE ). ±. RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED.7 ±. R =. TYP.9 ±.. REF PIN NOTCH R =. OR. CHAMFER. ±..7 ±. 7. ±.. REF.8 ±..9 ±.. ±.. REF.. R =. TYP. BSC BOTTOM IEW EXPOSED PAD (UFF) QFN 87 RE Ø. ±..99 ±. NOTE:. DRAWING IS NOT A JEDEC PACKAGE OUTLINE. DRAWING NOT TO SCALE. ALL DIMENSIONS ARE IN MILLIMETERS. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT ILUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED.mm ON ANY SIDE. EXPOSED PAD SHALL BE SOLDER PLATED. SHADED AREA IS ONLY A REFEREE FOR PIN LOCATION ON THE TOP AND BOTTOM OF PACKAGE 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. fb

16 LT- RELATED PARTS PART NUMBER DESCRIPTION COMMENTS Integrated Fiters LTC- ery Low Noise, 8 th Order Fiter Buiding Bock Lowpass and Bandpass Fiters up to khz LTC- khz Linear Phase Lowpass Fiter Continuous Time, 7 th Order, Differentia LTC- Low Noise,.MHz Lowpass Fiter Continuous Time, 7 th Order, Differentia LT8 ery Low Noise, th Order Fiter Buiding Bock Lowpass and Bandpass Fiters up to MHz LTC9-7 Linear Phase, Tunabe th Order Lowpass Fiter Singe-Resistor Programmabe Cut-Off to khz LT-. ery Low Noise Differentia.MHz Lowpass Fiter SNR = 8 at Suppy, th Order Fiter LT- ery Low Noise Differentia MHz Lowpass Fiter SNR = 8 at Suppy, th Order Fiter LT- ery Low Noise Differentia MHz Lowpass Fiter SNR = 8 at Suppy, th Order Fiter LT- ery Low Noise Differentia MHz Lowpass Fiter SNR = 7 at Suppy, th Order Fiter LT- ery Low Noise Differentia MHz Lowpass Fiter SNR = 7 at Suppy, th Order Fiter LT-. Dua ery Low Noise, Differentia Ampifi er and.mhz SNR = 8 at Suppy, th Order Fiter Lowpass Fiter LT- Dua ery Low Noise, Differentia Ampifi er and MHz SNR = 8 at Suppy, th Order Fiter Lowpass Fiter LT- Dua ery Low Noise, Differentia Ampifi er and MHz Lowpass Fiter SNR = 8 at Suppy, th Order Fiter fb LT 9 RE B PRINTED IN USA Linear Technoogy Corporation McCarthy Bvd., Mipitas, CA 9-77 (8) -9 FAX: (8) -7 LINEAR TECHNOLOGY CORPORATION 8