A bandpass filter is usually used to pass frequencies within a certain frequency range. If a high-performance opamp is used, such a filter can also be used at relatively high frequencies. As shown in the schematic diagram, here we have chosen an OPA603, which is a fast current-feedback opamp with a 100 MHz bandwidth for gain values between 1 and 10 (0 to 20 dB). If the circuit only has to handle a narrow range of frequencies, as in this case, the gain can be increased. With a current-feedback opamp, just as with an ordinary opamp, the negative feedback between the output and the inverting input determines the gain. In addition, the impedance of the feedback network determines the open-loop gain and the frequency response.
With the component values shown in the schematic diagram, signals outside the passband are attenuated by 22 dB. The center frequency of the filter is 10 MHz. As indicated by the printed formula, the center frequency can easily be altered. However, keep in mind that 10 MHz is roughly the maximum frequency at which this circuit can be used. The circuit can be powered by a supply voltage of ±15 V.
The OPA603 is a high-speed current-feedback op amp with guaranteed specifications at both ±5V and ±15V power supplies. It can deliver full ±10V signals into 150Ω loads with up to 1000V/µs slew rate. This allows it to drive terminated 75Ω cables. With 150mA peak output current capability it is suitable for driving load capacitance or long lines at high speed. In contrast with conventional op-amps, the current feedback approach provides nearly constant bandwidth and settling time over a wide range of closed-loop voltage gains. The OPA603 is available in a plastic 8-pin DIP and SO-16 surface-mount packages, specified over the industrial temperature range.
- WIDE SUPPLY RANGE: ±4.5 to ±18V
- BANDWIDTH: 100MHz, G = 1 to 10
- SLEW RATE: 1000V/µs
- FAST SETTLING TIME: 50ns to 0.1%
- HIGH OUTPUT CURRENT: ±150mA peak
- HIGH OUTPUT VOLTAGE: ±12V
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