LT1228 Linear Technology, LT1228 Datasheet
LT1228
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LT1228 Summary of contents
Page 1
... Current Feedback Amplifier with DC Gain Control D ESCRIPTIO The LT1228 makes it easy to electronically control the gain of signals from DC to video frequencies. The LT1228 implements gain control with a transconductance amplifier Input (voltage to current) whose gain is proportional to an exter- nally controlled current. A resistor is typically used to convert the output current to a voltage, which is then amplified with a current feedback amplifier ...
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... XI U Supply Voltage ...................................................... 18V Input Current, Pins (Note 7) ............ 15mA Output Short Circuit Duration (Note 1) ......... Continuous Operating Temperature Range LT1228C ................................................ LT1228M ........................................ – 125 C Storage Temperature Range ................. – 150 C Junction Temperature Plastic Package .............................................. 150 C Ceramic Package ............................................ 175 C Lead Temperature (Soldering, 10 sec) ...
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... 1kHz V 30mV 15V 12V 5V 15V 15V 5V LT1228 MIN TYP MAX UNITS 100 200 k 100 200 3 125 mA 25 125 ...
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... LT1228 ELECTRICAL C HARA TERISTICS C Transconductance Amplifier, Pins SYMBOL PARAMETER CMRR Common-Mode Rejection Ratio PSRR Power Supply Rejection Ratio g Transconductance m Transconductance Drift I Maximum Output Current OUT I Output Leakage Current OL V Maximum Output Voltage Swing OUT R Output Resistance O Output Capacitance (Note 2) ...
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... TEMPERATURE (°C) Output Saturation Voltage vs Temperature + V –0.5 –1.0 ± +1.0 +0.5 – V 200 –50 – TEMPERATURE (°C) LT1228 –55°C 25°C 125°C 50 100 150 200 LT1228 • TPC03 75 100 125 LT1228 • TPC06 V ±15V S 75 100 125 LT1228 • TPC09 5 ...
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... Bandwidth vs Supply Voltage, Gain = 100 500 SUPPLY VOLTAGE (±V) LT1228 • TPC17 = 1k = 750 PEAKING 0.5dB PEAKING 5dB LT1228 • TPC12 = 500 750 ...
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... TEMPERATURE (°C) Output Impedance vs Frequency 100 V = ±15V 0.1 0.01 0.001 10k 100k 1M 100M FREQUENCY (Hz) LT1228 2nd 3rd 100 LT1228 • TPC21 100 125 150 175 LT1228 • TPC24 = 750 10M 100M LT1228 • TPC27 7 ...
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... Current Feedback Amplifier, Pins 1, 6 & 8 Supply Current vs Supply Voltage –55° 125° 175° SUPPLY VOLTAGE (± GAIN V OUT – LT1228 • TA03 25° LT1228 • TPC30 ...
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... C (–3300ppm/ C) and the temperature co- efficient of the logging characteristic is 3300ppm important that the current into pin 5 be limited to less than 15mA. THE LT1228 WILL BE DESTROYED IF PIN 5 IS SHORTED TO GROUND OR TO THE POSITIVE SUPPLY. A limiting resistor (2k or so) should be used to prevent more than 15mA from flowing into pin 5 ...
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... The voltage at pin 5 also has a negative tempera- ture coefficient as described in the previous section. When the gain of several LT1228s are to be varied together, the current can be split equally by using equal value resistors to each pin 5. ...
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... A PPLICATI S I FOR ATIO compliance compatible with pin 5 of the LT1228. There- fore, the easiest way to digitally control the set current is to use a voltage output DAC and a voltage-to-current circuit. The previous voltage-to-current converter will take the output of any voltage output DAC and drive pin 5 with a proportional current ...
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... Boosting Bandwidth of High Gain Amplifier must have very low series CFA V OUT 8 – 510 5.1 LT1228 • TA08 with Capacitance On Inverting Input 4700pF 2200pF 100 FREQUENCY (MHz) LT1228 • TA09 ...
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... This is because the input stage and the output stage both have slew rate limitations. The input stage of the LT1228 current feedback amplifier slews at about 100V/ s before it becomes nonlinear. Faster input signals will turn on the normally reverse biased emitters on the input transistors and enhance the slew rate significantly ...
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... PPLICATI S I FOR ATIO Power Supplies The LT1228 amplifiers will operate from single or split supplies from 2V (4V total) to 18V (36V total not necessary to use equal value split supplies, however the offset voltage and inverting input bias current of the current feedback amplifier will degrade. The offset voltage changes about 350 V/V of supply mismatch, the inverting bias current changes about 2 ...
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... Therefore, the set currents remain high over most of the pot’s range, keeping the bandwidth over 15MHz even when the signal is attenuated 20dB. The pot is set up to completely turn off one LT1228 at each end of the rotation. S Video DC Restore (Clamp) Circuit ...
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... HARMONIC = –38dBc 3rd HARMONIC = –54 dBc FOR 5V OPERATION SHORT OUT 100 RESISTOR In this application the LT1228 is biased for operation from a single supply. An artificial signal ground at half supply voltage is generated with two 10k resistors and bypassed with a capacitor. A capacitor is used in series with R the DC gain of the current feedback amplifier to unity ...
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... Filters LOWPASS INPUT HIGHPASS INPUT Using the variable transconductance of the LT1228 to make variable filters is easy and predictable. The most straight forward way is to make an integrator by putting a capacitor at the output of the transconductance amp and buffering it with the current feedback amplifier. Because the input bias current of the current feedback amplifier must be supplied by the transconductance amplifier, the set current should not be operated below 10 A ...
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... C additional volt. The two 3k resistors divide the current between the two LT1228s. Therefore the set current of each amplifier goes from 800 A for a control voltage 4V. The resulting filter is at 100kHz for V equal zero, and changes it one octave/V of control input ...
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... –5V G 750 MODULATION INPUT 8V P–P OUTPUT 2V P–P 470 0.01µF 10k 4pF 10 4.7k –15V 1N4148’s LT1004 COUPLE THERMALLY 1.2V LT1228 • TA20 LT1228 • TA21 V OUT 6 0dBm(230mV) AT MODULATION = 750 LT1228 • TA22 LT1228 19 ...
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... LT1228 PACKAGE DESCRIPTIO 0.300 BSC (0.762 BSC) 0.008 – 0.018 0° – 15° (0.203 – 0.457) 0.045 – 0.068 0.385 ± 0.025 (1.143 – 1.727) (9.779 ± 0.635) 0.014 – 0.026 CORNER LEADS OPTION (0.360 – 0.660) (4 PLCS) 0.023 – 0.045 (0.584 – ...