LT1227 140MHz Video Current Feedback Amplifier U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO 140MHz Bandwidth: AV = 2, RL = 150Ω 1100V/µs Slew Rate Low Cost 30mA Output Drive Current 0.01% Differential Gain 0.01° Differential Phase High Input Impedance: 14MΩ, 3pF Wide Supply Range: ±2V to ±15V Shutdown Mode: IS < 250µA Low Supply Current: IS = 10mA Inputs Common Mode to Within 1.5V of Supplies Outputs Swing Within 0.8V of Supplies ■ ■ ■ Video Amplifiers Cable Drivers RGB Amplifiers Test Equipment Amplifiers 50Ω Buffers for Driving Mixers The LT1227 is manufactured on Linear Technology’s proprietary complementary bipolar process. , LTC and LT are registered trademarks of Linear Technology Corporation. U ■ A shutdown feature switches the device into a high impedance, low current mode, allowing multiple devices to be connected in parallel and selected. Input to output isolation in shutdown is 70dB at 10MHz for input amplitudes up to 10VP-P. The shutdown pin interfaces to open collector or open drain logic and takes only 4µs to enable or disable. The LT1227 comes in the industry standard pinout and can upgrade the performance of many older products. For a dual or quad version, see the LT1229/1230 data sheet. U APPLICATIO S ■ The LT®1227 is a current feedback amplifier with wide bandwidth and excellent video characteristics. The low differential gain and phase, wide bandwidth, and 30mA output drive current make the LT1227 well suited to drive cables in video systems. TYPICAL APPLICATIO Video Cable Driver Differential Gain and Phase vs Supply Voltage 0.20 + 75Ω LT1227 75Ω CABLE RF 1k VOUT VOUT =1 VIN 75Ω 0.16 0.16 0.12 0.12 0.08 0.08 ∆φ DIFFERENTIAL GAIN (%) – RG 1k 0.20 NTSC COMPOSITE f = 3.58MHz DIFFERENTIAL PHASE (DEG) VIN 0.04 0.04 1227 TA01 ∆G 0 5 7 11 13 9 SUPPLY VOLTAGE (±V) 15 0 LT1227 • TA02 1 LT1227 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage ..................................................... ±18V Input Current ...................................................... ±15mA Output Short Circuit Duration (Note 2) ........ Continuous Operating Temperature Range LT1227C .................................................. 0°C to 70°C LT1227M (OBSOLETE) .................... – 55°C to 125°C Storage Temperature Range ................. – 65°C to 150°C Junction Temperature Plastic Package ................................................ 150°C Ceramic Package (OBSOLETE) ........................ 175°C Lead Temperature (Soldering, 10 sec.)................ 300°C ORDER PART NUMBER TOP VIEW NULL 1 8 SHDN LT1227CN8 –IN 2 7 V+ +IN 3 6 OUT V– 4 5 NULL N8 PACKAGE 8-LEAD PLASTIC DIP TJMAX = 150°C, θJA = 100°C/W (N) J8 PACKAGE 8-LEAD CERAMIC DIP TJMAX = 175°C, θJA = 100°C/W (J) LT1227MJ8 OBSOLETE PACKAGE Consider the N8 Package for Alternate Source. ORDER PART NUMBER TOP VIEW NULL 1 8 SHDN –IN 2 7 V+ +IN 3 6 V– 4 LT1227CS8 OUT 5 NULL S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 150°C, θJA = 150°C/W 1227 Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCM = 0, ±5V ≤ VS ≤ ±15V, pulse tested, unless otherwise noted. SYMBOL VOS PARAMETER Input Offset Voltage IIN+ Input Offset Voltage Drift Noninverting Input Current CONDITIONS TA = 25°C MIN TYP ±3 ● 10 ±0.3 ● TA = 25°C ● IIN– Inverting Input Current ±10 TA = 25°C ● en +in –in RIN Input Noise Voltage Density Noninverting Input Noise Current Density Inverting Input Noise Current Density Input Resistance CIN Input Capacitance Input Voltage Range f = 1kHz, RF = 1k, RG = 10Ω, RS = 0Ω f = 1kHz f = 1kHz VIN = ±13V, VS = ±15V VIN = ±3V, VS = ±5V ● ● VS = ±15V, TA = 25°C ● VS = ±5V, TA = 25°C ● CMRR 2 Common Mode Rejection Ratio VS = ±15V, VCM = ±13V, TA = 25°C VS = ±15V, VCM = ±12V VS = ±5V, VCM = ±3V, TA = 25°C VS = ±5V, VCM = ±2V ● ● 1.5 1.5 ±13 ±12 ±3 ±2 55 55 55 55 3.2 1.7 32 14 11 3 ±13.5 ±3.5 62 61 MAX ±10 ±15 ±3 ±10 ±60 ±100 UNITS mV mV µV/°C µA µA µA µA nV/√Hz pA/√Hz pA/√Hz MΩ MΩ pF V V V V dB dB dB dB LT1227 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCM = 0, ±5V ≤ VS ≤ ±15V, pulse tested, unless otherwise noted. SYMBOL PSRR PARAMETER Inverting Input Current Common Mode Rejection Power Supply Rejection Ratio AV Noninverting Input Current Power Supply Rejection Inverting Input Current Power Supply Rejection Large-Signal Voltage Gain ROL Transresistance, ∆VOUT/∆IIN– VOUT Maximum Output Voltage Swing CONDITIONS VS = ±15V, VCM = ±13V, TA = 25°C VS = ±15V, VCM = ±12V VS = ±5V, VCM = ±3V, TA = 25°C VS = ±5V, VCM = ±2V VS = ±2V to ±15V, TA = 25°C VS = ±3V to ±15V VS = ±2V to ±15V, TA = 25°C VS = ±3V to ±15V VS = ±2V to ±15V, TA = 25°C VS = ±3V to ±15V VS = ±15V, VOUT = ±10V, RL = 1k VS = ±5V, VOUT = ±2V, RL = 150Ω VS = ±15V, VOUT = ±10V, RL = 1k VS = ±5V, VOUT = ±2V, RL = 150Ω VS = ±15V, RL = 400Ω, TA = 25°C MIN ● 4.5 ● ● 0.25 ● ● ● ● ● ● RL = 0Ω, TA = 25°C VS = ±15V, VOUT = 0V, TA = 25°C 55 55 100 100 ±12 ±10 ±3 ±2.5 30 VS = ±15V, Pin 8 Voltage = 0V, TA = 25°C ±3.7 60 10 120 ● I8 SR tr, tf BW tr, tf tS Shutdown Pin Current (Note 4) Output Leakage Current, Shutdown Slew Rate (Notes 5 and 6) Rise and Fall Time, VOUT = 1VP-P Small-Signal Bandwidth Small-Signal Rise and Fall Time Propagation Delay Small-Signal Overshoot Settling Time Differential Gain (Note 7) Differential Phase (Note 7) VS = ±15V VS = ±15V, Pin 8 Voltage = 0V, TA = 25°C TA = 25°C VS = ±5V, RF = 1k, RG = 1k, RL = 150Ω VS = ±15V, RF = 1k, RG = 1k, RL = 150Ω VS = ±15V, RF = 1k, RG = 1k, RL = 100Ω VS = ±15V, RF = 1k, RG = 1k, RL = 100Ω VS = ±15V, RF = 1k, RG = 1k, RL = 100Ω 0.1%, VOUT = 10V, RF = 1k, RG = 1k, RL = 1k VS = ±15V, RF = 1k, RG = 1k, RL = 150Ω VS = ±15V, RF = 1k, RG = 1k, RL = 1k VS = ±15V, RF = 1k, RG = 1k, RL = 150Ω VS = ±15V, RF = 1k, RG = 1k, RL = 1k Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: A heat sink may be required depending on the power supply voltage. Note 3: The supply current of the LT1227 has a negative temperature coefficient. For more information, see Typical Performance Characteristics curves. ● 500 50 50 5 5 72 72 270 240 ±13.5 ● Positive Supply Current, Shutdown MAX 10 10 10 10 80 2 ● Maximum Output Current Supply Current (Note 3) 60 60 ● VS = ±5V, RL = 150Ω, TA = 25°C IOUT IS TYP 3.5 1100 8.7 140 3.3 3.4 5 50 0.014 0.010 0.010 0.013 15.0 17.5 300 500 300 10 UNITS µA/V µA/V µA/V µA/V dB dB nA/V nA/V µA/V µA/V dB dB kΩ kΩ V V V V mA mA mA µA µA µA µA V/µs ns MHz ns ns % ns % % DEG DEG Note 4: Ramp Pin 8 voltage down from 15V while measuring IS. When IS drops to less than 0.5mA, measure Pin 8 current. Note 5: Slew rate is measured at ±5V on a ±10V output signal while operating on ±15V supplies with RF = 2k, RG = 220Ω and R L = 400Ω. Note 6: AC parameters are 100% tested on the ceramic and plastic DIP package parts (J and N suffix) and are sample tested on every lot of the SO packaged parts (S suffix). Note 7: NTSC composite video with an output level of 2V. 3 LT1227 U W TYPICAL PERFOR A CE CHARACTERISTICS Voltage Gain and Phase vs Frequency, Gain = 6dB 135 225 4 3 VS = ±15V RL = 100Ω RF = 910Ω 1 0 0.1 RF = 750Ω 100 RF = 1k 80 60 40 RF = 2k 20 0 1 10 FREQUENCY (MHz) 0 100 2 4 6 8 10 12 14 SUPPLY VOLTAGE (±V) LT1227 • TPC01 135 20 180 GAIN 225 18 17 16 VS = ±15V RL = 100Ω RF = 825Ω 15 14 0.1 120 100 RF = 250Ω RF = 500Ω 80 RF = 750Ω 60 RF = 1k 40 RF = 2k 41 135 40 180 225 37 35 34 0.1 VS = ±15V RL = 100Ω RF = 500Ω 2 4 6 8 10 12 14 SUPPLY VOLTAGE (±V) 16 100 18 RF = 500Ω 100 80 RF = 750Ω 60 RF = 1k 40 RF = 2k 0 18 2 4 6 8 10 12 14 SUPPLY VOLTAGE (±V) 18 16 16 14 14 RF = 500Ω RF = 1k 10 RF = 2k 8 18 LT1227 • TPC06 18 12 16 –3dB Bandwidth vs Supply Voltage, Gain = 100, RL = 1k 6 4 RF = 500Ω 12 RF = 1k RF = 2k 10 8 6 4 2 0 0 1 10 FREQUENCY (MHz) 120 20 2 LT1227 • TPC07 4 –3dB BANDWIDTH (MHz) VOLTAGE GAIN (dB) 90 PHASE SHIFT (DEG) 42 16 PEAKING ≤ 0.5dB PEAKING ≤ 5dB LT1227 • TPC05 0 38 6 8 10 12 14 SUPPLY VOLTAGE (±V) 0 0 45 GAIN 4 140 –3dB Bandwidth vs Supply Voltage, Gain = 100, RL = 100Ω PHASE 2 LT1227 • TPC03 0 100 44 36 0 –3dB Bandwidth vs Supply Voltage, Gain = 10, RL = 1k 140 Voltage Gain and Phase vs Frequency, Gain = 40dB 39 0 160 LT1227 • TPC04 43 40 180 20 1 10 FREQUENCY (MHz) RF = 1k 60 18 PEAKING ≤ 0.5dB PEAKING ≤ 5dB 160 –3dB BANDWIDTH (MHz) VOLTAGE GAIN (dB) 90 21 PHASE SHIFT (DEG) 45 22 19 16 180 0 PHASE RF = 1.5k 80 –3dB Bandwidth vs Supply Voltage, Gain = 10, RL = 100Ω 24 RF = 2k 100 LT1227 • TPC02 Voltage Gain and Phase vs Frequency, Gain = 20dB 23 RF = 750Ω 140 120 20 –3dB BANDWIDTH (MHz) 2 RF = 500Ω –3dB BANDWIDTH (MHz) 5 180 GAIN 140 120 PEAKING ≤ 0.5dB PEAKING ≤ 5dB 160 –3dB BANDWIDTH (MHz) 90 7 180 PEAKING ≤ 0.5dB PEAKING ≤ 5dB 160 –3dB BANDWIDTH (MHz) VOLTAGE GAIN (dB) 45 PHASE SHIFT (DEG) PHASE 8 6 180 0 10 9 –3dB Bandwidth vs Supply Voltage, Gain = 2, RL = 1k –3dB Bandwidth vs Supply Voltage, Gain = 2, RL = 100Ω 0 2 4 6 8 10 12 14 SUPPLY VOLTAGE (±V) 16 18 LT1227 • TPC08 0 2 4 6 8 10 12 14 SUPPLY VOLTAGE (±V) 16 18 LT1227 • TPC09 LT1227 U W TYPICAL PERFOR A CE CHARACTERISTICS Maximum Capacitive Load vs Feedback Resistor Total Harmonic Distortion vs Frequency 0.1 10000 VS = ±5V VS = ±15V 100 10 2 1 FEEDBACK RESISTOR (kΩ) VO = 7VRMS 3 1k 10k FREQUENCY (Hz) OUTPUT SATURATION VOLTAGE (V) –1.5 –2.0 2.0 1.5 V – = –2V TO –18V –0.5 70 RL = ∞ ±2V ≤ VS ≤ ±18V –1.0 1.0 0.5 50 25 0 75 TEMPERATURE (°C) 100 V– –50 –25 125 50 25 75 0 TEMPERATURE (°C) 80 POWER SUPPLY REJECTION (dB) SPOT NOISE (nV/√Hz OR pA/√Hz) 100 –in 10 en +in 1 1k 10k FREQUENCY (Hz) 50 40 30 –50 –25 125 100k LT1227 • TPC16 25 50 75 100 125 150 175 TEMPERATURE (°C) 0 LT1227 • TPC15 Power Supply Rejection vs Frequency Spot Noise Voltage and Current vs Frequency 100 60 LT1227 • TPC14 LT1227 • TPC13 10 100 Output Impedance vs Frequency 100 VS = ±15V RL = 100Ω RF = RG = 1k 60 POSITIVE NEGATIVE 40 20 VS = ±15V 10 OUTPUT IMPEDANCE (Ω) –25 100 Output Short-Circuit Current vs Junction Temperature 0.5 V– –50 10 FREQUENCY (MHz) LT1127 • TPC12 OUTPUT SHORT-CIRCUIT CURRENT (mA) V+ V+ 1.0 1 100k Output Saturation Voltage vs Temperature V + = 2V TO 18V AV = +2 LT1227 • TPC11 Input Common Mode Limit vs Temperature –1.0 AV = +1 10 0 100 LT1227 • TPC10 –0.5 AV = +10 AV = –1 15 5 VO = 1VRMS 0.001 10 1 0 0.01 VS = ±15V RL = 1k RF = 1k 20 OUTPUT VOLTAGE (VP-P) CAPACITIVE LOAD (pF) 1000 25 VS = ±15V RL = 400Ω RF = RG = 1k TOTAL HARMONIC DISTORTION (%) RL = 1k PEAKING ≤ 5dB GAIN = 2 COMMON MODE RANGE (V) Maximum Undistorted Output vs Frequency 1 RF = RG = 2k RF = RG = 1k 0.1 0.01 0 10k 100k 1M 10M FREQUENCY (Hz) 100M LT1227 • TPC17 0.001 10k 100k 1M 10M FREQUENCY (Hz) 100M LT1227 • TPC18 5 LT1227 U W TYPICAL PERFOR A CE CHARACTERISTICS Settling Time to 1mV vs Output Step Settling Time to 10mV vs Output Step 10 VS = ±15V RF = RG = 1k 8 13 12 4 NONINVERTING 2 INVERTING 0 –2 –4 4 2 NONINVERTING 0 INVERTING –2 –4 8 –8 5 60 40 SETTLING TIME (ns) 80 –10 100 4 4 0 12 16 8 SETTLING TIME (µs) 1M 10M FREQUENCY (Hz) 0.10 0.20 VS = ±15V AV = 2 RL = 1k RF = 1k RG = 1k 1M 10M 2ND 3RD –50 VS = ±15V AV = 2 RL = 1k RF = 1k RG = 1k 0.06 100k 1M –60 10M LT1227 • TPC24 Test Circuit for 3rd Order Intercept VS = ±15V RL = 100Ω RF = 680Ω RG = 75Ω 40 100M FREQUENCY (Hz) 3rd Order Intercept vs Frequency 3RD ORDER INTERCEPT (dBm) –40 0.04 LT1227 • TPC23 45 VS = ±15V VO = 2VP-P RL = 100Ω RF = 820Ω AV = 10dB –30 100M (VO)DC = 0.5V 1.0V 2.0V 0.03 0.05 LT1227 • TPC22 –20 0.02 FREQUENCY (Hz) 2nd and 3rd Harmonic Distortion vs Frequency 18 0.01 0.15 0.30 100k 100M 16 Differential Gain vs Frequency (VO)DC = 0.5V 1.0V 1.5V 2.0V 0.05 0.25 0.1 100k 6 8 10 12 14 SUPPLY VOLTAGE (±V) 0 DIFFERENTIAL GAIN (%) 1 4 LT1227 • TPC21 0 DIFFERENTIAL PHASE (DEG) 10 2 0 20 Differential Phase vs Frequency VS = ±15V AV = 1 RF = 1.5k 175°C LT1227 • TPC20 Output Impedance in Shutdown vs Frequency 100 125°C 7 –8 20 25°C 9 6 LT1227 • TPC19 OUTPUT IMPEDANCE (kΩ) 10 –6 0 –55°C 11 –6 –10 DISTORTION (dBc) SUPPLY CURRENT (mA) 6 OUTPUT STEP (V) OUTPUT STEP (V) VS = ±15V RF = RG = 1k 8 6 Supply Current vs Supply Voltage 14 10 + 50Ω LT1227 35 PO – 680Ω 30 25 75Ω 50Ω MEASURE INTERCEPT AT PO 20 1227 TC –70 1 10 FREQUENCY (MHz) 100 LT1227 • TPC25 6 15 0 10 20 30 40 FREQUENCY (MHz) 50 60 LT1227 • TPC26 LT1227 W W SI PLIFIED SCHE ATIC 7 14k NULL 1 V+ NULL 5 CURRENT SOURCE BIAS 8 S/D +IN 3 2 –IN 6 VOUT 4 V– 1227 SS U W U UO APPLICATI S I FOR ATIO The LT1227 is a very fast current feedback amplifier. Because it is a current feedback amplifier, the bandwidth is maintained over a wide range of voltage gains. The amplifier is designed to drive low impedance loads such as cables with excellent linearity at high frequencies. Feedback Resistor Selection The small-signal bandwidth of the LT1227 is set by the external feedback resistors and the internal junction capacitors. As a result, the bandwidth is a function of the supply voltage, the value of the feedback resistor, the closed-loop gain and load resistor. The characteristic curves of Bandwidth vs Supply Voltage show the effect of a heavy load (100Ω) and a light load (1k). These curves use a solid line when the response has less than 0.5dB of peaking and a dashed line when the response has 0.5dB to 5dB of peaking. The curves stop where the response has more than 5dB of peaking. At a gain of two, on ±15V supplies with a 1k feedback resistor, the bandwidth into a light load is over 140MHz, but into a heavy load the bandwidth reduces to 120MHz. The loading has this effect because there is a mild resonance in the output stage that enhances the bandwidth at light loads but has its Q reduced by the heavy load. This enhancement is only useful at low gain settlings; at a gain of ten it does not boost the bandwidth. At unity gain, the enhancement is so effective the value of the feedback resistor has very little effect. At very high closed-loop gains, the bandwidth is limited by the gain bandwidth product of about 1GHz. The curves show that the bandwidth at a closed-loop gain of 100 is 12MHz, only one tenth what it is at a gain of two. 7 LT1227 U W U UO APPLICATI S I FOR ATIO and inverting input bias current will change. The offset voltage changes about 500µV per volt of supply mismatch. The inverting bias current can change as much as 5.0µA per volt of supply mismatch, though typically the change is less than 0.5µA per volt. Small-Signal Rise Time, AV = +2 Slew Rate VOUT RF = 1k, RG= 1k, RL = 100Ω AI01 Capacitance on the Inverting Input Current feedback amplifiers require resistive feedback from the output to the inverting input for stable operation. Take care to minimize the stray capacitance between the output and the inverting input. Capacitance on the inverting input to ground will cause peaking in the frequency response (and overshoot in the transient response), but it does not degrade the stability of the amplifier. Capacitive Loads The LT1227 can drive capacitive loads directly when the proper value of feedback resistor is used. The graph of Maximum Capacitive Load vs Feedback Resistor should be used to select the appropriate value. The value shown is for 5dB peaking when driving a 1k load at a gain of 2. This is a worst case condition, the amplifier is more stable at higher gains and driving heavier loads. Alternatively, a small resistor (10Ω to 20Ω) can be put in series with the output to isolate the capacitive load from the amplifier output. This has the advantage that the amplifier bandwidth is only reduced when the capacitive load is present and the disadvantage that the gain is a function of the load resistance. The slew rate of a current feedback amplifier is not independent of the amplifier gain configuration the way slew rate is in a traditional op amp. This is because both the input stage and the output stage have slew rate limitations. In the inverting mode, and for higher gains in the noninverting mode, the signal amplitude between the input pins is small and the overall slew rate is that of the output stage. For gains less than ten in the noninverting mode, the overall slew rate is limited by the input stage. The input stage slew rate of the LT1227 is approximately 125V/µs and is set by internal currents and capacitances. The output slew rate is set by the value of the feedback resistors and the internal capacitances. At a gain of ten with a 1k feedback resistor and ±15V supplies, the output slew rate is typically 1100V/µs. Larger feedback resistors will reduce the slew rate as will lower supply voltages, similar to the way the bandwidth is reduced. The graph of Maximum Undistorted Output vs Frequency relates the slew rate limitations to sinusoidal inputs for various gain configurations. Large-Signal Transient Response, AV = +10 VOUT Power Supplies The LT1227 will operate from single or split supplies from ±2V (4V total) to ±15V (30V total). It is not necessary to use equal value split supplies, however the offset voltage 8 RF = 910Ω, RG= 100Ω, RL = 400Ω AI02 LT1227 U W U UO APPLICATI S I FOR ATIO Shutdown Large-Signal Transient Response, AV = +2 VOUT RF = 1k, RG= 1k, RL = 400Ω AI03 Large-Signal Transient Response, AV = –2 The LT1227 has a high impedance, low supply current mode which is controlled by Pin 8. In the shutdown mode, the output looks like a 12pF capacitor and the supply current drops to approximately the Pin 8 current. The shutdown pin is referenced to the positive supply through an internal pullup circuit (see the simplified schematic). Pulling a current of greater than 50µA from Pin 8 will put the device into the shutdown mode. An easy way to force shutdown is to ground Pin 8, using open drain (collector) logic. Because the pin is referenced to the positive supply, the logic used should have a breakdown voltage of greater than the positive supply voltage. No other circuitry is necessary as an internal JFET limits the Pin 8 current to about 100µA. When Pin 8 is open, the LT1227 operates normally. Differential Input Signal Swing VOUT AI04 RF = 1k, RG= 510Ω, RL = 400Ω AI04 The differential input swing is limited to about ±6V by an ESD protection device connected between the inputs. In normal operation, the differential voltage between the input pins is small, so this clamp has no effect; however, in the shutdown mode, the differential swing can be the same as the input swing. The clamp voltage will then set the maximum allowable input voltage. To allow for some margin, it is recommended that the input signal be less than ±5V when the device is shutdown. Offset Adjust Settling Time The characteristic curves show that the LT1227 amplifier settles to within 10mV of final value in 40ns to 55ns for any output step up to 10V. The curve of settling to 1mV of final value shows that there is a slower thermal contribution up to 20µs. The thermal settling component comes from the output and the input stage. The output contributes just under 1mV per volt of output change and the input contributes 300µV per volt of input change. Fortunately the input thermal tends to cancel the output thermal. For this reason the noninverting gain of two configuration settles faster than the inverting gain of one. Pins 1 and 5 are provided for offset nulling. A small current to V + or ground will compensate for DC offsets in the device. The pins are referenced to the positive supply (see the simplified schematic) and should be left open if unused. The offset adjust pins act primarily on the inverting input bias current. A 10k pot connected to Pins 1 and 5 with the wiper connected to V + will null out the bias current, but will not affect the offset voltage much. Since the output offset is VO ≅ AV • VOS + (IIN –) • RF at higher gains (AV > 5), the VOS term will dominate. To null out the VOS term, use a 10k pot between Pins 1 and 5 with a 150k resistor from the wiper to ground for 15V split supplies, 47k for 5V split supplies. 9 LT1227 UO TYPICAL APPLICATI S MUX Amplifier MUX Amplifier The shutdown function can be effectively used to construct a MUX amplifier. A two-channel version is shown, but more inputs could be added with suitable logic. By configuring each amplifier as a unity-gain follower, there is no loading by the feedback network when the amplifier is off. The open drains of the 74C906 buffers are used to interface the 5V logic to the shutdown pin. Feedthrough from the unselected input to the output is –70dB at 10MHz. The differential voltage between MUX inputs VIN1 and VIN2 appears across the inputs of the shutdown device, this voltage should be less than ±5V to avoid turning on the clamp diodes discussed previously. If the inputs are sinusoidal having a zero DC level, this implies that the amplitude of each input should be less than 5VP-P. The output impedance of the off amplifier remains high until the output level exceeds approximately 6VP-P at 10MHz, this sets the maximum usable output level. Switching time between inputs is about 4µs without an external pullup. Adding a 10k pullup resistor from each shutdown pin to V + will reduce the switching time to 2µs but will increase the positive supply current in shutdown by 1.5mA. 15V + VIN1 LT1227 S/D VOUT – –15V 1.5k VOUT =1 VIN 5V 74C906 15V + VIN2 LT1227 S/D – –15V 1.5k 5V 5V INPUT SELECT 74HC04 74C906 1227 TA04 MUX Output MUX Input Crosstalk vs Frequency –40 INPUT CROSSTALK (dB) –50 VOUT INPUT SELECT –60 –70 –80 –90 VIN1 = 1VP-P, VIN2 = 0V TA03 1 10 FREQUENCY (MHz) 100 LT1227 TA05 10 LT1227 U PACKAGE DESCRIPTIO J8 Package 8-Lead CERDIP (Narrow .300 Inch, Hermetic) (Reference LTC DWG # 05-08-1110) 0.300 BSC (0.762 BSC) 0.008 – 0.018 (0.203 – 0.457) CORNER LEADS OPTION (4 PLCS) 0° – 15° 0.023 – 0.045 (0.584 – 1.143) HALF LEAD OPTION 0.045 – 0.068 (1.143 – 1.727) FULL LEAD OPTION NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE OR TIN PLATE LEADS 0.405 (10.287) MAX 0.005 (0.127) MIN 0.015 – 0.060 (0.381 – 1.524) 8 0.014 – 0.026 (0.360 – 0.660) 0.100 (2.54) BSC 5 0.025 (0.635) RAD TYP 0.220 – 0.310 (5.588 – 7.874) 1 0.045 – 0.065 (1.143 – 1.651) 6 7 2 3 4 0.200 (5.080) MAX 0.125 3.175 MIN J8 1298 OBSOLETE PACKAGE N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) 0.300 – 0.325 (7.620 – 8.255) 0.045 – 0.065 (1.143 – 1.651) 0.065 (1.651) TYP 0.009 – 0.015 (0.229 – 0.381) ( 0.400* (10.160) MAX 0.130 ± 0.005 (3.302 ± 0.127) 8 7 6 5 1 2 3 4 0.255 ± 0.015* (6.477 ± 0.381) +0.035 0.325 –0.015 +0.889 8.255 –0.381 ) 0.100 (2.54) BSC 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003 (0.457 ± 0.076) N8 1098 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm) S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.014 – 0.019 (0.355 – 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 8 7 6 5 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) SO8 1298 1 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 2 3 4 11 LT1227 UO TYPICAL APPLICATI S Single Supply AC-Coupled Amplifier Noninverting Single Supply AC-Coupled Amplifier Inverting 3.58MHz Oscillator 15V 5V 5V 4.7µF + + AV = 10k 22µF 100pF 10k 2.2µF – 3.579545MHz + + VOUT 75pF 10k + LT1227 2N3904 510Ω ≈ 10 RS + 51Ω BW = 14Hz to 60MHz + VIN 1N4148 100k 4.7µF 1k VOUT LT1227 10k 68pF 150k 15V – – 220µF 510Ω RS VIN AV = 11 BW = 14Hz to 60MHz + + 51Ω 51Ω VOUT LT1227 220µF 510Ω 51Ω + 1227 TA09 –15V 1227 TA08 Buffer with DC Nulling Loop CMOS Logic to Shutdown Interface 1227 TA10 Optional Offset Nulling Circuit V+ 180Ω RNULL 180Ω 10k 3 0.1µF 3 VIN 5 + 1 LT1227 10k 2 V+ 15V 10k 7 3 + 6 LT1227 6 2 VOUT 1 LT1227 2 8 – 5 – 4 4 –15V V– – 10k 7 + 6 RNULL = 47k FOR VS = ±5V RNULL = 150k FOR VS = ±15V 1227 TA12 5V 1.5k 10k 2N3904 100k 0.01µF 1227 TA11 + 100k LT1097 – 0.01µF 1227 TA07 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1395/LT1396/LT1397 Single/Dual/Quad 400MHz Current Feedback Amplifier 12 Linear Technology Corporation Miniature Packages: SOT-23, MSOP-8, SSOP-16 1227fb LT/CP 1001 1.5K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 1994