Datasheet LT1227 (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | 140MHz Video Current Feedback Amplifier |
| Pages / Page | 12 / 8 — APPLICATI. S I FOR ATIO. Small-Signal Rise Time, AV = +2. Slew Rate. … |
| File Format / Size | PDF / 255 Kb |
| Document Language | English |
APPLICATI. S I FOR ATIO. Small-Signal Rise Time, AV = +2. Slew Rate. Capacitance on the Inverting Input. Capacitive Loads
Model Line for this Datasheet
Text Version of Document
LT1227
O U U W U APPLICATI S I FOR ATIO Small-Signal Rise Time, AV = +2
and inverting input bias current will change. The offset voltage changes about 500µV per volt of supply mis- match. 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.
Slew Rate
VOUT 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 AI01 noninverting mode, the signal amplitude between the RF = 1k, RG= 1k, RL = 100Ω input pins is small and the overall slew rate is that of the output stage. For gains less than ten in the noninverting
Capacitance on the Inverting Input
mode, the overall slew rate is limited by the input stage. Current feedback amplifiers require resistive feedback The input stage slew rate of the LT1227 is approximately from the output to the inverting input for stable operation. 125V/µs and is set by internal currents and capacitances. Take care to minimize the stray capacitance between the The output slew rate is set by the value of the feedback output and the inverting input. Capacitance on the invert- resistors and the internal capacitances. At a gain of ten ing input to ground will cause peaking in the frequency with a 1k feedback resistor and ±15V supplies, the output response (and overshoot in the transient response), but it slew rate is typically 1100V/µs. Larger feedback resistors does not degrade the stability of the amplifier. will reduce the slew rate as will lower supply voltages, similar to the way the bandwidth is reduced.
Capacitive Loads
The graph of Maximum Undistorted Output vs Frequency The LT1227 can drive capacitive loads directly when the relates the slew rate limitations to sinusoidal inputs for proper value of feedback resistor is used. The graph of various gain configurations. Maximum Capacitive Load vs Feedback Resistor should be used to select the appropriate value. The value shown
Large-Signal Transient Response, A
is for 5dB peaking when driving a 1k load at a gain of 2. This
V = +10
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 band- V width is only reduced when the capacitive load is present OUT and the disadvantage that the gain is a function of the load resistance.
Power Supplies
The LT1227 will operate from single or split supplies from ±2V (4V total) to ±15V (30V total). It is not necessary to RF = 910Ω, RG= 100Ω, RL = 400Ω AI02 use equal value split supplies, however the offset voltage 8
O U U W U APPLICATI S I FOR ATIO Small-Signal Rise Time, AV = +2
and inverting input bias current will change. The offset voltage changes about 500µV per volt of supply mis- match. 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.
Slew Rate
VOUT 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 AI01 noninverting mode, the signal amplitude between the RF = 1k, RG= 1k, RL = 100Ω input pins is small and the overall slew rate is that of the output stage. For gains less than ten in the noninverting
Capacitance on the Inverting Input
mode, the overall slew rate is limited by the input stage. Current feedback amplifiers require resistive feedback The input stage slew rate of the LT1227 is approximately from the output to the inverting input for stable operation. 125V/µs and is set by internal currents and capacitances. Take care to minimize the stray capacitance between the The output slew rate is set by the value of the feedback output and the inverting input. Capacitance on the invert- resistors and the internal capacitances. At a gain of ten ing input to ground will cause peaking in the frequency with a 1k feedback resistor and ±15V supplies, the output response (and overshoot in the transient response), but it slew rate is typically 1100V/µs. Larger feedback resistors does not degrade the stability of the amplifier. will reduce the slew rate as will lower supply voltages, similar to the way the bandwidth is reduced.
Capacitive Loads
The graph of Maximum Undistorted Output vs Frequency The LT1227 can drive capacitive loads directly when the relates the slew rate limitations to sinusoidal inputs for proper value of feedback resistor is used. The graph of various gain configurations. Maximum Capacitive Load vs Feedback Resistor should be used to select the appropriate value. The value shown
Large-Signal Transient Response, A
is for 5dB peaking when driving a 1k load at a gain of 2. This
V = +10
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 band- V width is only reduced when the capacitive load is present OUT and the disadvantage that the gain is a function of the load resistance.
Power Supplies
The LT1227 will operate from single or split supplies from ±2V (4V total) to ±15V (30V total). It is not necessary to RF = 910Ω, RG= 100Ω, RL = 400Ω AI02 use equal value split supplies, however the offset voltage 8
