a FEATURES High Dynamic Range Output IP3: +28 dBm: Re 50 @ 250 MHz Low Noise Figure: 5.9 dB @ 250 MHz Two Gain Versions: AD8350-15: 15 dB AD8350-20: 20 dB -3 dB Bandwidth: 1.0 GHz Single Supply Operation: 5 V to 10 V Supply Current: 28 mA Input/Output Impedance: 200 Single-Ended or Differential Input Drive 8-Lead SOIC Package and 8-Lead microSOIC Package Low Distortion 1.0 GHz Differential Amplifier AD8350 FUNCTIONAL BLOCK DIAGRAM 8-Lead SOIC and SOIC Packages (with Enable) IN+ 1 ENBL 2 + - VCC 3 OUT+ 4 8 IN- 7 GND 6 GND 5 OUT- AD8350 APPLICATIONS Cellular Base Stations Communications Receivers RF/IF Gain Block Differential A-to-D Driver SAW Filter Interface Single-Ended-to-Differential Conversion High Performance Video High Speed Data Transmission PRODUCT DESCRIPTION The AD8350 series are high performance fully-differential amplifiers useful in RF and IF circuits up to 1000 MHz. The amplifier has excellent noise figure of 5.9 dB at 250 MHz. It offers a high output third order intercept (OIP3) of +28 dBm at 250 MHz. Gain versions of 15 dB and 20 dB are offered. The amplifier can be operated down to 5 V with an OIP3 of +28 dBm at 250 MHz and slightly reduced distortion performance. The wide bandwidth, high dynamic range and temperature stability make this product ideal for the various RF and IF frequencies required in cellular, CATV, broadband, instrumentation and other applications. The AD8350 is designed to meet the demanding performance requirements of communications transceiver applications. It enables a high dynamic range differential signal chain, with exceptional linearity and increased common-mode rejection. The device can be used as a general purpose gain block, an A-to-D driver, and high speed data interface driver, among other functions. The AD8350 input can also be used as a singleended-to-differential converter. The AD8350 is offered in an 8-lead single SOIC package and SOIC package. It operates from 5 V and 10 V power supplies, drawing 28 mA typical. The AD8350 offers a power enable function for power-sensitive applications. The AD8350 is fabricated using Analog Devices' proprietary high speed complementary bipolar process. The device is available in the industrial (-40C to +85C) temperature range. REV. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 2001 (@ 25C, VS = 5 V, G = 15 dB, unless otherwise noted. All specifications refer to AD8350-SPECIFICATIONS differential inputs and differential outputs unless noted.) Parameter DYNAMIC PERFORMANCE -3 dB Bandwidth Bandwidth for 0.1 dB Flatness Slew Rate Settling Time Gain (S21)1 Gain Supply Sensitivity Gain Temperature Sensitivity Isolation (S12)1 NOISE/HARMONIC PERFORMANCE 50 MHz Signal Second Harmonic Third Harmonic Output Second Order Intercept2 Output Third Order Intercept2 250 MHz Signal Second Harmonic Third Harmonic Output Second Order Intercept2 Output Third Order Intercept2 1 dB Compression Point (RTI)2 Voltage Noise (RTI) Noise Figure INPUT/OUTPUT CHARACTERISTICS Differential Offset Voltage (RTI) Differential Offset Drift Input Bias Current Input Resistance CMRR Output Resistance POWER SUPPLY Operating Range Quiescent Current Power-Up/Down Switching Power Supply Rejection Ratio Conditions Min VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VOUT = 1 V p-p 0.1%, VOUT = 1 V p-p VS = 5 V, f = 50 MHz VS = 5 V to 10 V, f = 50 MHz TMIN to TMAX f = 50 MHz 14 Typ 0.9 1.1 90 90 2000 10 15 0.003 -0.002 -18 Max 16 Unit GHz GHz MHz MHz V/s ns dB dB/V dB/C dB VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VS = 5 V VS = 10 V VS = 5 V VS = 10 V -66 -67 -65 -70 58 58 28 29 dBc dBc dBc dBc dBm dBm dBm dBm VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VS = 5 V VS = 10 V VS = 5 V VS = 10 V VS = 5 V VS = 10 V f = 150 MHz f = 150 MHz -48 -49 -52 -61 39 40 24 28 2 5 1.7 6.8 dBc dBc dBc dBc dBm dBm dBm dBm dBm dBm nV/Hz dB VOUT+ - VOUT- TMIN to TMAX 1 0.02 15 200 -67 200 mV mV/C A dB Real f = 50 MHz Real Powered Up, VS = 5 V Powered Down, VS = 5 V Powered Up, VS = 10 V Powered Down, VS = 10 V 4 25 3 27 3 f = 50 MHz, VS = 1 V p-p OPERATING TEMPERATURE RANGE -40 28 3.8 30 4 15 -58 11.0 32 5.5 34 6.5 V mA mA mA mA ns dB +85 C NOTES 1 See Tables II-III for complete list of S-Parameters. 2 Re: 50 . Specifications subject to change without notice. -2- REV. A AD8350 AD8350-20-SPECIFICATIONS (@ 25C, V = 5 V, G = 20 dB, unless otherwise noted. All specifications refer to S differential inputs and differential outputs unless noted.) Parameter DYNAMIC PERFORMANCE -3 dB Bandwidth Bandwidth for 0.1 dB Flatness Slew Rate Settling Time Gain (S21)1 Gain Supply Sensitivity Gain Temperature Sensitivity Isolation (S12)1 NOISE/HARMONIC PERFORMANCE 50 MHz Signal Second Harmonic Third Harmonic Output Second Order Intercept2 Output Third Order Intercept2 250 MHz Signal Second Harmonic Third Harmonic Output Second Order Intercept2 Output Third Order Intercept2 1 dB Compression Point (RTI)2 Voltage Noise (RTI) Noise Figure INPUT/OUTPUT CHARACTERISTICS Differential Offset Voltage (RTI) Differential Offset Drift Input Bias Current Input Resistance CMRR Output Resistance POWER SUPPLY Operating Range Quiescent Current Power-Up/Down Switching Power Supply Rejection Ratio Conditions Min VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VOUT = 1 V p-p 0.1%, VOUT = 1 V p-p VS = 5 V, f = 50 MHz VS = 5 V to 10 V, f = 50 MHz TMIN to TMAX f = 50 MHz 0.7 0.9 90 90 2000 15 20 0.003 -0.002 -22 Max 21 Unit GHz GHz MHz MHz V/s ns dB dB/V dB/C dB VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VS = 5 V VS = 10 V VS = 5 V VS = 10 V -65 -66 -66 -70 56 56 28 29 dBc dBc dBc dBc dBm dBm dBm dBm VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VS = 5 V, VOUT = 1 V p-p VS = 10 V, VOUT = 1 V p-p VS = 5 V VS = 10 V VS = 5 V VS = 10 V VS = 5 V VS = 10 V f = 150 MHz f = 150 MHz -45 -46 -55 -60 37 38 24 28 -2.6 1.8 1.7 5.6 dBc dBc dBc dBc dBm dBm dBm dBm dBm dBm nV/Hz dB VOUT+ - VOUT- TMIN to TMAX 1 0.02 15 200 -52 200 mV mV/C A dB Real f = 50 MHz Real Powered Up, VS = 5 V Powered Down, VS = 5 V Powered Up, VS = 10 V Powered Down, VS = 10 V 4 25 3 27 3 f = 50 MHz, VS = 1 V p-p OPERATING TEMPERATURE RANGE -40 NOTES 1 See Tables II-III for complete list of S-Parameters. 2 Re: 50 . REV. A 19 Typ -3- 28 3.8 30 4 15 -45 11.0 32 5.5 34 6.5 V mA mA mA mA ns dB +85 C AD8350 PIN FUNCTION DESCRIPTIONS ABSOLUTE MAXIMUM RATINGS* Supply Voltage, VS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 V Input Power Differential . . . . . . . . . . . . . . . . . . . . . . +8 dBm Internal Power Dissipation . . . . . . . . . . . . . . . . . . . . 400 mW JA SOIC (R) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100C/W JA SOIC (RM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133C/W Maximum Junction Temperature . . . . . . . . . . . . . . . . . 125C Operating Temperature Range . . . . . . . . . . . -40C to +85C Storage Temperature Range . . . . . . . . . . . . -65C to +150C Lead Temperature Range (Soldering 60 sec) . . . . . . . . . 300C *Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. PIN CONFIGURATION IN+ 1 8 AD8350 Pin Function Description 1, 8 IN+, IN- 2 ENBL 3 4, 5 VCC OUT+, OUT- 6, 7 GND Differential Inputs. IN+ and IN- should be ac-coupled (pins have a dc bias of midsupply). Differential input impedance is 200 . Power-up Pin. A high level (5 V) enables the device; a low level (0 V) puts device in sleep mode. Positive Supply Voltage. 5 V to 10 V. Differential Outputs. OUT+ and OUT- should be ac-coupled (pins have a dc bias of midsupply). Differential input impedance is 200 . Common External Ground Reference. IN- GND TOP VIEW VCC 3 (Not to Scale) 6 GND ENBL 2 OUT+ 4 7 5 OUT- ORDERING GUIDE Model Temperature Range Package Description Package Option Brand Code AD8350AR15 AD8350AR15-REEL AD8350AR15-REEL7 AD8350ARM15 AD8350ARM15-REEL AD8350ARM15-REEL7 AD8350AR20 AD8350AR20-REEL AD8350AR20-REEL7 AD8350ARM20 AD8350ARM20-REEL AD8350ARM20-REEL7 AD8350-EVAL -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C 8-Lead SOIC 8-Lead SOIC 13" Reel 8-Lead SOIC 7" Reel 8-Lead microSOIC 8-Lead microSOIC 13" Reel 8-Lead microSOIC 7" Reel 8-Lead SOIC 8-Lead SOIC 13" Reel 8-Lead SOIC 7" Reel 8-Lead microSOIC 8-Lead microSOIC 13" Reel 8-Lead microSOIC 7" Reel SOIC Evaluation Board SO-8 SO-8 SO-8 RM-8 RM-8 RM-8 SO-8 SO-8 SO-8 RM-8 RM-8 RM-8 Standard Standard Standard J2N J2N J2N Standard Standard Standard J2P J2P J2P CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD8350 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. -4- WARNING! ESD SENSITIVE DEVICE REV. A Typical Performance Characteristics-AD8350 20 25 VCC = 10V 40 15 30 VCC = 5V 20 10 5 VCC = 5V 15 10 10 VCC = 5V 0 -40 -20 0 20 40 TEMPERATURE - C 0 60 80 1 10 100 1k FREQUENCY - MHz 5 10k TPC 2. AD8350-15 Gain (S21) vs. Frequency TPC 1. Supply Current vs. Temperature 500 300 300 400 VCC = 10V 200 VCC = 5V 250 VCC = 10V 200 1 10 100 FREQUENCY - MHz TPC 4. AD8350-15 Input Impedance vs. Frequency 10 100 FREQUENCY - MHz 1k TPC 5. AD8350-20 Input Impedance vs. Frequency 800 10k SOIC SOIC 100 0 1 1k 100 1k FREQUENCY - MHz 200 100 100 10 300 VCC = 5V 150 150 IMPEDANCE - 350 250 1 TPC 3. AD8350-20 Gain (S21) vs. Frequency 350 IMPEDANCE - IMPEDANCE - 20 VCC = 10V GAIN - dB VCC = 10V GAIN - dB SUPPLY CURRENT - mA 50 0 10 100 FREQUENCY - MHz 1000 TPC 6. AD8350-15 Output Impedance vs. Frequency -5 -10 -10 -15 ISOLATION - dB IMPEDANCE - 400 SOIC 200 0 -15 VCC = 10V -20 0 100 10 FREQUENCY - MHz 1000 TPC 7. AD8350-20 Output Impedance vs. Frequency REV. A ISOLATION - dB SOIC 600 VCC = 10V -20 -25 -30 1 10 100 1k FREQUENCY - MHz 10k TPC 8. AD8350-15 Isolation (S12) vs. Frequency -5- VCC = 5V -25 VCC = 5V 1 10 100 1k FREQUENCY - MHz 10k TPC 9. AD8350-20 Isolation (S12) vs. Frequency AD8350 -40 -45 -40 VOUT = 1V p-p -45 HD2 (VCC = 5V) -55 HD3 (VCC = 5V) -60 -65 HD3 (VCC = 10V) -50 HD2 (VCC = 10V) -55 -60 -65 -70 -70 -75 -75 -80 0 50 100 150 200 250 300 FUNDAMENTAL FREQUENCY - MHz TPC 10. AD8350-15 Harmonic Distortion vs. Frequency -45 FO = 50MHz -80 -65 HD2 (VCC = 10V) -85 0 HD3 (VCC = 10V) OIP2 - dBm (Re: 50) HD2 (VCC = 10V) -75 50 100 150 200 250 300 FUNDAMENTAL FREQUENCY - MHz 0 0.5 1 1.5 2 2.5 3 OUTPUT VOLTAGE - V p-p 66 66 61 61 VCC = 10V 56 51 VCC = 5V 46 36 3.5 TPC 13. AD8350-20 Harmonic Distortion vs. Differential Output Voltage 50 100 150 200 FREQUENCY - MHz 250 31 26 VCC = 5V 16 100 150 200 FREQUENCY - MHz 250 300 VCC = 10V 31 26 21 TPC 16. AD8350-15 Output Referred IP3 vs. Frequency 11 VCC = 10V 51 VCC = 5V 46 0 10.0 VCC = 5V 16 50 3.5 0 50 100 150 200 FREQUENCY - MHz 250 300 TPC 17. AD8350-20 Output Referred IP3 vs. Frequency -6- 50 100 150 200 FREQUENCY - MHz 250 300 TPC 15. AD8350-20 Output Referred IP2 vs. Frequency 1dB COMPRESSION - dBm (Re: 50) VCC = 10V 0 1 1.5 2 2.5 3 OUTPUT VOLTAGE - V p-p 56 36 300 36 OIP3 - dBm (Re: 50) OIP3 - dBm (Re: 50) 0 41 36 11 0.5 41 TPC 14. AD8350-15 Output Referred IP2 vs. Frequency 41 21 0 TPC 12. AD8350-15 Harmonic Distortion vs. Differential Output Voltage 41 -85 HD3 (VCC = 10V) -75 HD3 (VCC = 10V) HD2 (VCC = 5V) HD3 (VCC = 5V) DISTORTION - dBc HD3 (VCC = 5V) TPC 11. AD8350-20 Harmonic Distortion vs. Frequency -55 -65 HD3 (VCC = 5V) HD2 (VCC = 5V) -55 OIP2 - dBm (Re: 50) -50 FO = 50MHz HD2 (VCC = 5V) DISTORTION - dBc HD2 (VCC = 10V) DISTORTION - dBc DISTORTION - dBc -45 VOUT = 1V p-p INPUT REFERRED VCC = 10V 7.5 5.0 2.5 0 VCC = 5V -2.5 -5.0 0 100 200 300 400 FREQUENCY - MHz 500 600 TPC 18. AD8350-15 1 dB Compression vs. Frequency REV. A AD8350 10 10 9 9 5.0 VCC = 10V 0 -2.5 -7.5 100 200 300 400 FREQUENCY - MHz 500 VCC = 5V 600 TPC 19. AD8350-20 1 dB Compression vs. Frequency 25 AD8350-20 OUTPUT OFFSET - mV AD8350-15 5 0 -5 0 2 3 4 5 6 7 VCC - Volts 8 9 10 TPC 22. AD8350 Gain (S21) vs. Supply Voltage -20 -20 50 -30 VOUT + (VCC = 5V) 0 VOUT - (VCC = 5V) -50 -100 VOUT + (VCC = 10V) -250 -40 VOUT - (VCC = 10V) 0 20 40 TEMPERATURE - C 60 80 VCC = 5V VOUT PSRR - dB -50 AD8350-15 -70 ENBL -80 5V 30ns -90 1k TPC 25. AD8350 CMRR vs. Frequency REV. A AD8350-20 -60 AD8350-15 -80 AD8350-20 10 100 FREQUENCY - MHz 50 100 150 200 250 300 350 400 450 500 FREQUENCY - MHz -90 -20 500mV -40 -50 -70 -150 TPC 23. AD8350 Output Offset Voltage vs. Temperature VCC = 5V 1 0 -40 -30 -60 VCC = 5V TPC 21. AD8350-20 Noise Figure vs. Frequency 100 -200 -15 1 5 50 100 150 200 250 300 350 400 450 500 FREQUENCY - MHz -10 -20 VCC = 10V 7 VCC = 5V 15 10 8 6 TPC 20. AD8350-15 Noise Figure vs. Frequency 20 GAIN - dB 7 5 0 VCC = 10V 6 VCC = 5V -5.0 8 PSRR - dB 2.5 NOISE FIGURE - dB INPUT REFERRED NOISE FIGURE - dB 1dB COMPRESSION - dBm (Re: 50) 7.5 TPC 26. AD8350 Power-Up/Down Response Time -7- 1 10 100 FREQUENCY - MHz 1k TPC 24. AD8350 PSRR vs. Frequency AD8350 APPLICATIONS Using the AD8350 Figure 1 shows the basic connections for operating the AD8350. A single supply in the range 5 V to 10 V is required. The power supply pin should be decoupled using a 0.1 F capacitor. The ENBL pin is tied to the positive supply or to 5 V (when VCC = 10 V) for normal operation and should be pulled to ground to put the device in sleep mode. Both the inputs and the outputs have dc bias levels at midsupply and should be ac-coupled. 8 R S /2 SOURCE C4 0.001F 6 5 CP + RLOAD R S /2 1 L S /2 2 3 4 CAC L S /2 CAC 0.1F ENBL (5V) +VS (5V TO 10V) Figure 3. Reactively Matching the Input and Output LOAD CAC LS 7 6 - CP Z = 100 8 7 L S /2 AD8350 VS Also shown in Figure 1 are the impedance balancing requirements, either resistive or reactive, of the input and output. With an input and output impedance of 200 , the AD8350 should be driven by a 200 source and loaded by a 200 impedance. A reactive match can also be implemented. C2 0.001F CAC CAC L S /2 CAC LS 5 AD8350 8 RS - 7 6 5 AD8350 + Z = 200 - CP CP RLOAD + VS 1 2 3 4 Z = 100 1 C1 0.001F C3 0.001F C5 0.1F ENBL (5V) +VS (5V TO 10V) Figure 4. Single-Ended Equivalent Circuit When the source impedance is smaller than the load impedance, a step-up matching network is required. A typical step-up network is shown on the input of the AD8350 in Figure 3. For purely resistive source and load impedances the resonant approach may be used. The input and output impedance of the AD8350 can be modeled as a real 200 resistance for operating frequencies less than 100 MHz. For signal frequencies exceeding 100 MHz, classical Smith Chart matching techniques should be invoked in order to deal with the complex impedance relationships. Detailed S parameter data measured differentially in a 200 system can be found in Tables II and III. LOAD 7 6 5 C4 0.001F AD8350 - For the input matching network the source resistance is less than the input resistance of the AD8350. The AD8350 has a nominal 200 input resistance from Pins 1 to 8. The reactance of the ac-coupling capacitors, CAC, should be negligible if 100 nF capacitors are used and the lowest signal frequency is greater than 1 MHz. If the series reactance of the matching network inductor is defined to be XS = 2 f LS, and the shunt reactance of the matching capacitor to be XP = (2 f CP)-1, then: Z = 200 + 1 Z = 200 C1 0.001F ENBL (5V) CAC 0.1F Figure 2 shows how the AD8350 can be driven by a singleended source. The unused input should be ac-coupled to ground. When driven single-endedly, there will be a slight imbalance in the differential output voltages. This will cause an increase in the second order harmonic distortion (at 50 MHz, with VCC = 10 V and VOUT = 1 V p-p, -59 dBc was measured for the second harmonic on AD8350-15). SOURCE 4 ENBL (5V) Figure 1. Basic Connections for Differential Drive 8 3 CAC +VS (5V TO 10V) C2 0.001F 2 2 3 4 C3 0.001F C5 0.1F +VS (5V TO 10V) XS = Figure 2. Basic Connections for Single-Ended Drive Reactive Matching RS x RLOAD where X P = RLOAD x XP RS RLOAD - RS (1) For a 70 MHz application with a 50 source resistance, and assuming the input impedance is 200 , or RLOAD = RIN = 200 , then XP = 115.5 and XS = 86.6 , which results in the following component values: In practical applications, the AD8350 will most likely be matched using reactive matching components as shown in Figure 3. Matching components can be calculated using a Smith Chart or by using a resonant approach to determine the matching network that results in a complex conjugate match. In either situation, the circuit can be analyzed as a single-ended equivalent circuit to ease calculations as shown in Figure 4. CP = (2 x 70 x 106 x 115.5)-1 = 19.7 pF and LS = 86.6 x (2 x 70 x 106)-1 = 197 nH -8- REV. A AD8350 For the output matching network, if the output source resistance of the AD8350 is greater than the terminating load resistance, a step-down network should be employed as shown on the output of Figure 3. For a step-down matching network, the series and parallel reactances are calculated as: RS x RLOAD where X P = RS x XP XS = RLOAD RS - RLOAD (2) The same results could be found using a Smith Chart as shown in Figure 7. In this example, a shunt capacitor and a series inductor are used to match the 200 source to a 50 load. For a frequency of 10 MHz, the same capacitor and inductor values previously found using the resonant approach will transform the 200 source to match the 50 load. At frequencies exceeding 100 MHz, the S parameters from Tables II and III should be used to account for the complex impedance relationships. For a 10 MHz application with the 200 output source resistance of the AD8350, RS = 200 , and a 50 load termination, RLOAD = 50 , then XP = 115.5 and X S = 86.6 , which results in the following component values: CP = (2 x 10 x 106 x 115.5)-1 = 138 pF and LS = 86.6 x (2 x 10 x 106)-1 = 1.38 H LOAD The same results can be obtained using the plots in Figure 5 and Figure 6. Figure 5 shows the normalized shunt reactance versus the normalized source resistance for a step-up matching network, RS < RLOAD. By inspection, the appropriate reactance can be found for a given value of RS/RLOAD. The series reactance is then calculated using XS = RS RLOAD/XP. The same technique can be used to design the step-down matching network using Figure 6. SOURCE SHUNT C SERIES L NORMALIZED REACTANCE - XP /RLOAD 2 1.8 Figure 7. Smith Chart Representation of Step-Down Network RSOURCE XS 0.8 After determining the matching network for the single-ended equivalent circuit, the matching elements need to be applied in a differential manner. The series reactance needs to be split such that the final network is balanced. In the previous examples, this simply translates to splitting the series inductor into two equal halves as shown in Figure 3. 0.6 Gain Adjustment 1.6 RLOAD XP 1.4 1.2 1 0.4 0 0.01 0.05 0.09 0.13 0.17 0.21 0.25 0.29 0.33 0.37 0.41 0.45 0.49 0.53 0.57 0.61 0.65 0.69 0.73 0.77 0.2 NORMALIZED SOURCE RESISTANCE - RSOURCE /R LOAD Figure 5. Normalized Step-Up Matching Components 3.2 XS RLOAD XP 2.8 2.6 2.4 8.8 8 8.4 7.6 7.2 6.8 6 6.4 5.6 5.2 4.8 4 4.4 3.6 3.2 2.8 2 2 2.2 2.4 NORMALIZED REACTANCE - XP/RLOAD RSOURCE 3 The effective gain of the AD8350 can be reduced using a number of techniques. Obviously a matched attenuator network will reduce the effective gain, but this requires the addition of a separate component which can be prohibitive in size and cost. The attenuator will also increase the effective noise figure resulting in an SNR degradation. A simple voltage divider can be implemented using the combination of the driving impedance of the previous stage and a shunt resistor across the inputs of the AD8350 as shown in Figure 8. This provides a compact solution but suffers from an increased noise spectral density at the input of the AD8350 due to the thermal noise contribution of the shunt resistor. The input impedance can be dynamically altered through the use of feedback resistors as shown in Figure 9. This will result in a similar attenuation of the input signal by virtue of the voltage divider established from the driving source impedance and the reduced input impedance of the AD8350. Yet this technique does not significantly degrade the SNR with the unnecessary increase in thermal noise that arises from a truly resistive attenuator network. NORMALIZED SOURCE RESISTANCE - RSOURCE/R LOAD Figure 6. Normalized Step-Down Matching Components REV. A -9- AD8350 CAC RS The insertion loss and the resultant power gain for multiple shunt resistor values is summarized in Table I. The source resistance and input impedance need careful attention when using Equation 1. The reactance of the input impedance of the AD8350 and the ac-coupling capacitors need to be considered before assuming they have negligible contribution. Figure 10 shows the effective power gain for multiple values of RSHUNT for the AD8350-15 and AD8350-20. CAC 8 7 RSHUNT 6 5 RL AD8350 - + VS RS RL RSHUNT 1 2 3 4 Table I. Gain Adjustment Using Shunt Resistor, RS = 100 and RIN = 100 Single-Ended CAC CAC 0.1F ENBL (5V) +VS (5V TO 10V) Figure 8. Gain Reduction Using Shunt Resistor RFEXT CAC CAC 8 RS 7 6 5 RSHUNT- IL-dB Power Gain-dB AD8350-15 AD8350-20 50 100 200 300 400 6.02 3.52 1.94 1.34 1.02 8.98 11.48 13.06 13.66 13.98 20 RL AD8350 18 - 16 AD8350-20 + VS 13.98 16.48 18.06 18.66 18.98 14 RL 1 CAC 2 3 4 0.1F ENBL (5V) GAIN - dB RS CAC +VS (5V TO 10V) 12 AD8350-15 10 8 6 4 RFEXT 2 Figure 9. Dynamic Gain Reduction 0 0 Figure 8 shows a typical implementation of the shunt divider concept. The reduced input impedance that results from the parallel combination of the shunt resistor and the input impedance of the AD8350 adds attenuation to the input signal effectively reducing the gain. For frequencies less than 100 MHz, the input impedance of the AD8350 can be modeled as a real 200 resistance (differential). Assuming the frequency is low enough to ignore the shunt reactance of the input, and high enough such that the reactance of moderately sized ac-coupling capacitors can be considered negligible, the insertion loss, IL, due to the shunt divider can be expressed as: RIN ( R IN + RS ) IL ( dB ) = 20 x Log10 RIN RSHUNT ( RIN RSHUNT + RS ) where RIN RSHUNT 100 200 300 400 500 RSHUNT - 600 700 800 Figure 10. Gain for Multiple Values of Shunt Resistance for Circuit in Figure 8 The gain can be adjusted dynamically by employing external feedback resistors as shown in Figure 9. The effective attenuation is a result of the lowered input impedance as with the shunt resistor method, yet there is no additional noise contribution at the input of the device. It is necessary to use well-matched resistors to minimize common-mode offset errors. Quality 1% tolerance resistors should be used along with a symmetric board layout to help guarantee balanced performance. The effective gain for multiple values of external feedback resistors is shown in Figure 11. (3) R x RSHUNT and RIN = 100 single - ended = IN RIN + RSHUNT -10- REV. A AD8350 Driving Lighter Loads 20 It is not necessary to load the output of the AD8350 with a 200 differential load. Often it is desirable to try to achieve a complex conjugate match between the source and load in order to minimize reflections and conserve power. But if the AD8350 is driving a voltage responding device, such as an ADC, it is no longer necessary to maximize power transfer. The harmonic distortion performance will actually improve when driving loads greater than 200 . The lighter load requires less current driving capability on the output stages of the AD8350 resulting in improved linearity. Figure 12 shows the improvement in second and third harmonic distortion for increasing differential load resistance. 18 AD8350-20 16 GAIN - dB 14 12 10 AD8350-15 8 6 4 2 0 0 500 1000 RFEXT - 1500 2000 -66 Figure 11. Power Gain vs. External Feedback Resistors for the AD8350-15 and AD8350-20 with R S = 100 and RL = 100 -68 DISTORTION - dBc -70 The power gain of any two-port network is dependent on the source and load impedance. The effective gain will change if the differential source and load impedance is not 200 . The singleended input and output resistance of the AD8350 can be modeled using the following equations: HD3 -72 -74 -76 -78 RIN RF + RL = RF + RL + 1 + gm x RL RINT HD2 -80 (4) -82 200 300 400 500 600 700 800 900 1000 RLOAD - and 1 1 1 + RS RINT = 1 1 + gm x 1 1 + RS RINT Figure 12. Second and Third Harmonic Distortion vs. Differential Load Resistance for the AD8350-15 with VS = 5 V, f = 70 MHz, and VOUT = 1 V p-p RF + ROUT RF + RS for RS 1 k 1 + gm x RS (5) where = RFEXT//RFINT RF R FEXT = R Feedback External RFINT = 662 for the AD8350-15 = 1100 for the AD8350-20 RINT = 25000 gm = 0.066 mhos for the AD8350-15 = 0.110 mhos for the AD8350-20 = R Source (Single-Ended) RS RL = R Load (Single-Ended) = R Input (Single-Ended) R IN R OUT = R Output (Single-Ended) The resultant single-ended gain can be calculated using the following equation: GV = REV. A RL x ( gm x RF - 1) RL + RS + RF + RL x RS x gm (6) -11- AD8350 EVALUATION BOARD To drive and load the board differentially, transformers T1 and T2 should be removed and replaced with four 0 resistors (0805 size); Resistors R1 and R4 (0 ) should also be removed. This yields a circuit with a broadband input and output impedance of 200 . To match to impedances other than this, matching components (0805 size) can be placed on pads C1, C2, C3, C4, L1, and L2. Figure 13 shows the schematic of the AD8350 evaluation board, for SOIC, as it is shipped from the factory. The board is configured to allow easy evaluation using single-ended 50 test equipment. The input and output transformers have a 4-to-1 impedance ratio and transform the AD8350's 200 input and output impedances to 50 . In this mode, 0 resistors (R1 and R4) are required. To allow compensation for the insertion loss of the transformers, a calibration path is provided at Test In and Test Out. This consists of two transformers connected back to back. C3 0.001F C1 0.001F IN- T1: TC4-1W (MINI CIRCUITS) 6 1 7 8 5 6 AD8350 R2 0 - L1 (OPEN) L2 (OPEN) + R1 0 R3 0 T2: TC4-1W (MINI CIRCUITS) 1 IN+ R4 0 OUT- 6 OUT+ 1 2 3 4 C2 0.001F +VS TEST IN C4 0.001F A 3 B 2 C5 0.1F SW1 1 T3: TC4-1W (MINI CIRCUITS) 6 1 +VS T4: TC4-1W (MINI CIRCUITS) TEST OUT 1 6 Figure 13. Evaluation Board -12- REV. A AD8350 Table II. Typical Scattering Parameters for the AD8350-15: V CC = 5 V, Differential Input and Output, Z SOURCE(diff) = 200 , ZLOAD(diff) = 200 Frequency - MHz S11 S12 S21 S22 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500 0.015-48.8 0.028-65.7 0.043-75.3 0.057-87.5 0.073-91.8 0.080-95.6 0.100-97.4 0.111-99.1 0.128-103.2 0.141-106.7 0.151-109.7 0.161-111.9 0.179-114.7 0.187-117.4 0.194-121 0.199-121.2 0.215-122.6 0.225-127.0 0.225-127.7 0.244-129.9 0.119176.3 0.119171.1 0.119166.9 0.120163.5 0.119159.8 0.120154.8 0.117151.2 0.121147.3 0.120143.7 0.120140.3 0.120136.6 0.123132.9 0.121130.7 0.122126.6 0.123123.6 0.124120.1 0.126117.2 0.126113.9 0.126112 0.128108.1 5.60-4.3 5.61-8.9 5.61-13.5 5.61-17.9 5.65-22.6 5.68-27.0 5.73-31.8 5.78-36.3 5.83-41.0 5.90-45.6 6.02-50.2 6.14-55.1 6.19-60.2 6.27-65.0 6.43-70.1 6.61-75.8 6.77-81.7 6.91-87.6 7.06-93.8 7.27-99.8 0.034-4.8 0.032-14.3 0.036-30.2 0.043-39.6 0.053-40.6 0.058-37 0.072-45.1 0.077-47.7 0.091-52.5 0.104-55.1 0.108-54.2 0.122-51.5 0.135-55.6 0.150-56.9 0.162-60.9 0.187-60.3 0.215-63.3 0.242-63.9 0.268-65.2 0.304-68.2 Table III. Typical Scattering Parameters for the AD8350-20: V CC = 5 V, Differential Input and Output, Z SOURCE(diff) = 200 , ZLOAD(diff) = 200 Frequency - MHz S11 S12 S21 S22 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500 0.017-142.9 0.033-114.9 0.055-110.6 0.073-109.4 0.089-112.1 0.098-116.5 0.124-118.1 0.141-119.4 0.159-122.6 0.170-128.5 0.186-131.6 0.203-132.9 0.215-135.0 0.222-136.9 0.242-142.4 0.240-145.2 0.267-146.7 0.266-150.7 0.267-153.7 0.285-161.1 0.074174.9 0.074171.0 0.075167.0 0.075163.1 0.075159.2 0.076153.8 0.075150.2 0.076147.2 0.077142.2 0.078139.5 0.078135.8 0.080132.5 0.080129.3 0.082125.9 0.082123.6 0.084120.3 0.084117.3 0.086115.1 0.087112.8 0.088110.9 9.96-4.27 9.98-8.9 9.98-13.3 10.00-17.7 10.12-22.1 10.20-26.4 10.34-30.9 10.50-35.6 10.65-40.1 10.80-44.7 11.14-49.3 11.45-54.7 11.70-60.3 11.93-65.0 12.39-70.3 12.99-76.8 13.34-84.0 13.76-90.1 14.34-97.5 14.89-105.0 0.023-16.6 0.022-2.7 0.023-23.5 0.029-22.7 0.037-18.0 0.045-3.2 0.055-15.7 0.065-15.6 0.080-17.7 0.085-22.4 0.096-23.5 0.116-25.9 0.139-29.6 0.161-32.2 0.173-38.6 0.207-37.6 0.241-48.1 0.265-49.7 0.317-53.5 0.359-59.2 REV. A -13- AD8350 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 8-Lead Plastic SOIC (SO-8) 0.1968 (5.00) 0.1890 (4.80) 0.1574 (4.00) 0.1497 (3.80) 8 5 1 4 0.2440 (6.20) 0.2284 (5.80) PIN 1 0.0196 (0.50) 45 0.0099 (0.25) 0.0500 (1.27) BSC 0.0688 (1.75) 0.0532 (1.35) 0.0098 (0.25) 0.0040 (0.10) 8 0.0098 (0.25) 0 0.0500 (1.27) 0.0160 (0.41) 0.0075 (0.19) 0.0192 (0.49) 0.0138 (0.35) SEATING PLANE 8-Lead microSOIC Package (RM-8) 0.122 (3.10) 0.114 (2.90) 8 5 0.199 (5.05) 0.187 (4.75) 0.122 (3.10) 0.114 (2.90) 1 4 PIN 1 0.0256 (0.65) BSC 0.120 (3.05) 0.112 (2.84) 0.006 (0.15) 0.002 (0.05) 0.018 (0.46) SEATING 0.008 (0.20) PLANE 0.120 (3.05) 0.112 (2.84) 0.043 (1.09) 0.037 (0.94) 0.011 (0.28) 0.003 (0.08) -14- 33 27 0.028 (0.71) 0.016 (0.41) REV. A -15- -16- PRINTED IN U.S.A. C01014-1.5-6/01(A)