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OPA684 Datasheet(PDF) 10 Page - Burr-Brown (TI) |
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OPA684 Datasheet(HTML) 10 Page - Burr-Brown (TI) |
10 / 24 page OPA694 SBOS319C − SEPTEMBER 2004 − REVISED NOVEMBER 2004 www.ti.com 10 APPLICATION INFORMATION WIDEBAND CURRENT FEEDBACK OPERATION The OPA694 provides exceptional AC performance for a wideband, low-power, current-feedback operational amplifier. Requiring only 5.8mA quiescent current, the OPA694 offers a 690MHz bandwidth at a gain of +2, along with a 1700V/ µs slew rate. An improved output stage provides ±80mA output drive, along with < 1.5V output voltage headroom. This combination of low power and high bandwidth can benefit high-resolution video applications. Figure 1 shows the DC-coupled, gain of +2, dual power- supply circuit configuration used as the basis of the ±5V Electrical Characteristic tables and Typical Characteristic curves. For test purposes, the input impedance is set to 50 Ω with a resistor to ground and the output impedance is set to 50 Ω with a series output resistor. Voltage swings reported in the Electrical Charateristics are taken directly at the input and output pins, while load powers (dBm) are defined at a matched 50 Ω load. For the circuit of Figure 1, the total effective load will be 100 Ω || 804Ω = 89Ω. One optional component is included in Figure 1. In addition to the usual power-supply decoupling capacitors to ground, a 0.1 µF capacitor is included between the two power-supply pins. In practical PC board layouts, this optional added capacitor will typically improve the 2nd-harmonic distortion performance by 3dB to 6dB. OPA694 +5V + −5V −V S +V S 50 ΩLoad 50 Ω 50 Ω V O V I 50 ΩSource R G 402 Ω R F 402 Ω 6.8 µF 0.1 µF6.8µF 0.1 µF 0.1 µF Figure 1. DC-Coupled, G = +2, Bipolar-Supply Specification and Test Circuit Figure 2 shows the DC-coupled, gain of −2V/V, dual power-supply circuit used as the basis of the inverting Typical Characteristic curves. Inverting operation offers several performance benefits. Since there is no common-mode signal across the input stage, the slew rate for inverting operation is higher and the distortion performance is slightly improved. An additional input resistor, RT, is included in Figure 2 to set the input impedance equal to 50 Ω. The parallel combination of RT and RG sets the input impedance. Both the noninverting and inverting applications of Figure 1 and Figure 2 will benefit from optimizing the feedback resistor (RF) value for bandwidth (see the discussion in Setting Resistor Values to Optimize Bandwidth). The typical design sequence is to select the RF value for best bandwidth, set RG for the gain, then set RT for the desired input impedance. As the gain increases for the inverting configuration, a point will be reached where RG will equal 50Ω, where RT is removed and the input match is set by RG only. With RG fixed to achieve an input match to 50 Ω, RF is simply increased, to increase gain. This will, however, quickly reduce the achievable bandwidth, as shown by the inverting gain of –10 frequency response in the Typical Characteristic curves. For gains > 10V/V (14dB at the matched load), noninverting operation is recommended to maintain broader bandwidth. OPA694 +5V +V S −V S −5V 50 ΩLoad 50 Ω 20 Ω R T 66.5 Ω R G 200 Ω 6.8 µF 0.1 µF 6.8 µF 0.1 µF Optional 0.01 µF V I 50 ΩSource R F 402 Ω V O Figure 2. DC-Coupled, G = −2V/V, Bipolar-Supply Specification and Test Circuit |
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