The EL5166 and EL5167 are current-feedback amplifiers with an extremely high bandwidth of 1.4GHz at a gain of +1 and a high bandwidth of 800MHz at a gain of +2. This makes these amplifiers ideal for today's high-speed video and surveillance applications, as well as some RF and IF frequency designs.

The EL5166 and EL5167 amplifiers have a supply current of only 8.5mA and can operate from a single supply voltage of 5V to 12V , providing very high performance and low power consumption.

The EL5166 also integrates an enable and disable function that reduces the typical supply current to 13µA per amplifier, and the amplifier can be enabled by leaving the CE pin floating or applying a low logic level. The EL5167 is available in a 5 Ld SOT-23 package and the EL5166 is available in a 6 Ld SOT-23 package and an industry standard 8 Ld SOIC package. Both amplifiers operate over the industrial temperature range of -40°C to +85°C.

The EL5166 and EL5167 operate from a supply voltage range of 5V to 10V and are also capable of swinging to within 1V of the output voltage. Due to their current feedback topology, the EL5166 and EL5167 do not have the normal gain bandwidth products associated with voltage feedback op amps. Conversely, their -3dB bandwidth remains relatively constant as the closed-loop gain increases. The combination of high bandwidth and low power consumption, along with a competitive price, makes the EL5166 and EL5167 ideal for many low power/high bandwidth applications such as portable, handheld or battery powered devices.

Application Information

The EL5166 and EL5167 are current-feedback operational amplifiers, which provide a low supply current of 8.5mA per amplifier of 1.4GHz and a wide -3dB bandwidth. The EL5166 and EL5167 operate with supply voltages ranging from a single 5V to 10V and they are also capable of swinging within 1V on either supply on the output. Because of their current feedback topologies, the EL5166 and EL5167 do not have op amps that correlate normally with the voltage feedback gain-bandwidth product. Instead, their -3dB bandwidth maintains a relatively constant closed-loop gain increase. This high bandwidth and low power consumption, combined with aggressive pricing makes the EL5166 and EL5167 ideal choices for many low power/high bandwidth applications such as portable, handheld or battery powered devices.

Inverted 200mA output current distribution amplification fi er:

board layout

As with any high frequency device, good printed circuit board layout is necessary for optimum performance. A low impedance ground plane structure is necessary. Surface mount components are recommended, but if leaded components are used, lead lengths should be as short as possible. The power supply pins must be well bypassed to reduce the risk of oscillation. A 4.7µF combined tantalum capacitor in parallel with a 0.01µF capacitor has proven to work well when placed on each power supply pin. For good AC performance, parasitic capacitance should be kept to a minimum, especially at the inverting input. Even in the case of a ground plane structure, it should be removed from the adjacent inverting input to minimize any stray area capacitance at that node. Carbon or metal film resistors are slightly less acceptable than metal film resistors for peaking and inductance due to the additional series bandwidth. The use of sockets, especially for SO encapsulation, should be avoided as much as possible. Sockets add parasitic inductance and capacitance, which can cause additional peaking and overshoot.

Precision amplifiers with fast settling times:

Disable/Power Down

The EL5166 amplifier can be disabled, putting its output in a high impedance state. When disabled, the amplifier's supply current is reduced to 13µA. When the EL5166 is disabled, its CE pin is pulled up to 1V within the positive supply. Similarly, the amplifier is powered by floating or pulling its CE active pin at least 3V below the positive supply. For ±5V supplies, this means that an EL5166 amplifier will be enabled when CE is 2V or lower, and disabled when CE is above 4V. Although the logic levels are not standard TTL, this choice of logic voltage allows the EL5166 to be CE enabled by tying it to ground, even in single 5V supply applications. The CE pin can be driven from the CMOS output.

Capacitance at the inverting input Stray capacitance at the inverting input of any manufacturer's high-speed voltage or current feedback amplifier can be affected. For inverting gain, this parasitic capacitance has little effect because the inverting input is on virtual ground. But for non-inverting gain, this capacitor (together with the feedback and gain resistors) creates a pole in the amplifier's feedback path. Such poles, if low enough, have the same destabilizing effect in frequency as the forward open-loop response is zero. The use of large value feedback and gain resistors exacerbates this problem by further reducing the pole frequency (increasing the likelihood of oscillation). The EL5166 and EL5167 frequency responses are optimized for resistor values used in Figure 3. The high bandwidth of these amplifiers, these resistor values can cause stability problems when parasitic combined with capacitance, thus ground planes are not recommended around the amplifier's inverting input terminals.

Feedback resistor value

The EL5166 and EL5167 have been designed and specified to have an RF of approximately 392 Ω at a gain of +2. This value of the feedback resistor gives a -3dB bandwidth of 800MHz for a V=2 of about 0.5dB of peak shaving. Since the EL5166 and EL5167 are current feedback amplifiers, the value of R can also be changed to obtain more bandwidth. As shown in the curve frequency response for different RF and RG on page 4, the bandwidth "Typical Performance Curve" and the peak value can be easily modified by changing the value of the feedback resistor. Since the EL5166 and EL5167 are current feedback amplifiers, their gain-bandwidth product is not a constant different from the closed-loop gain. This feature actually allows the EL5166 and EL5167 to maintain a fairly stable gain with -3dB bandwidth difference. As the gain increases, the bandwidth decreases slightly and increases steadily. The self-loop stability improves with the increased closed-loop gain, so it is possible to reduce the value of RF below a specified 250Ω and still retain stability, resulting in only a slight loss of bandwidth for the increased closed-loop gain.

Video performance

For good video performance, the amplifier needs to maintain the same output impedance and at the same frequency response as the DC level is being changed at the output. It is especially difficult to find a standard 150Ω because of the variation in the output current of the video load with the DC level. Previously, good differential gain could only be achieved by running the output transistors through high idle currents (to reduce skewed output impedance). These currents are typically comparable to the entire 8.5mA supply current of each EL5166 and EL5167 amplifiers. Special circuits have been incorporated into the EL5166 and EL5167 to reduce the variation of output impedance with current output. This results in dG and DP specifications of 0.01% and 0.03° while driving 150Ω at a gain of 2.

Differential Line Driver/Receiver: