JUNE ? Applications incude audio, signal conditioning, and sensor amplification. The OPA family of op amps are well-suited for cell phone power amplifier control loops. Special features include excellent common-mode rejection ratio CMRR , no input stage crossover distortion, high input impedance and rail-to-rail input and output swing.
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JUNE ? CMRR: dB min? Rail-to-Rail Input and Output? Applications incude audio, signal conditioning, and sensor amplification. The OPA family of op amps are also well-suited for cell phone power amplifier control loops. Special features include an excellent common-mode rejection ratio CMRR , no input stage crossover distortion, high input impedance, and rail-to-rail input and output swing. The input common-mode range includes both the negative and positive supplies.
The output voltage swing is within 10mV of the rails. All versions are specified for operation from? Single and dual versions have identical specifications for maximum design flexibility. Low Offset: ? Low Input Bias Current: 0. U1 OPA R1 7. All trademarks are the property of their respective owners. Products conform to specifications per the terms of Texas Instruments standard warranty.
Production processing does not necessarily include testing of all parameters. Continuous Operating Temperature. Exposure to absolute maximum conditions for extended periods may degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those specified is not supported. Input signals that can swing more than 0. This integrated circuit can be damaged by ESD.
Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
V Offset Voltage Drift? Many of the specifications apply from? Parameters that can exhibit significant variance with regard to operating voltage or temperature are presented in the Typical Characteristics. R2 10k? To realize the full operational performance of the device, good high-frequency printed circuit board PCB layout practices are required. Low-loss, 0. F bypass capacitors must be connected between each supply pin and ground as close to the device as possible. The bypass capacitor traces should be designed for minimum inductance.
A typical dual-supply connection is shown in Figure 1, which is accompanied by a single-supply connection. The OPA is configured as a basic inverting amplifier with a gain of? The dual-supply connection has an output voltage centered on zero, while the single? For the circuit shown, this voltage is 1. Supply Connection Figure 1. The divider also provides the bias voltage for the electret element. In the case of input and output pins, this protection primarily consists of current steering diodes connected between the input and power-supply pins.
These ESD protection diodes also provide in-circuit, input overdrive protection, provided that the current is limited to 10mA as stated in the Absolute Maximum Ratings.
Figure 3 shows how a series input resistor may be added to the driven input to limit the input current. The added resistor contributes thermal noise at the amplifier input and its value should be kept to the minimum in noise-sensitive applications.
A unique zer? This topology also allows the OPA to provide superior common-mode performance over the entire input range, which extends mV beyond both power-supply rails, as shown in Figure 4.
Clean 3. F Figure 2. Figure 3. Mode Voltage V Figure 4. As with all op amps, there may be specific instances where the OPA can become unstable, leading to oscillation. The particular op amp circuit configuration, layout, gain and output loading are some of the factors to consider when establishing whether an amplifier will be stable in operation.
The capacitive load, in conjunction with the op amp output resistance, creates a pole within the feedback loop that degrades the phase margin. The degradation of the phase margin increases as the capacitive loading increases. When operating in the unity-gain configuration, the OPA remains stable with a pure capacitive load up to approximately 1nF. F is sufficient to alter the phase characteristics in the feedback loop such that the amplifier remains stable. Increasing the amplifier closed-loop gain allows the amplifier to drive increasingly larger capacitance.
This increased capability is evident when observing the overshoot response of the amplifier at higher voltage gains. See the typical characteristic graph, Small-Signal Overshoot vs. Capacitive Load. One technique for increasing the capacitive load drive capability of the amplifier operating in unity gain is to insert a small resistor, typically 10?
This resistor significantly reduces the overshoot and ringing associated with large capacitive loads. A possible problem with this technique is that a voltage divider is created with the added series resistor and any resistor connected in parallel with the capacitive load.
The voltage divider introduces a gain error at the output that reduces the output swing. The error contributed by the voltage divider may be insignificant. However, when RL is decreased to ? Furthermore, the deviation from 0V only becomes greater as the load current required increases. This increased deviation is a result of limitations of the CMOS output stage. When a pull-down resistor is connected from the amplifier output to a negative voltage source, the OPA can achieve an output level of 0V, and even a few millivolts below 0V.
Below this limit, nonlinearity and limiting conditions become evident. Figure 7 illustrates a circuit using this technique. A pull-down current of approximately ? A is required when OPA is connected as a unity-gain buffer. A practical termination voltage VNEG is?
Keep in mind that lower termination voltages result in smaller pull-down resistors that load the output during positive output voltage excursions. Note that this technique does not work with all op amps and should only be applied to op amps such as the OPA that have been specifically designed to operate in this manner.
Also, operating the OPA output at 0V changes the output stage operating conditions, resulting in somewhat lower open-loop gain and bandwidth. Keep these precautions in mind when driving a capacitive load because these conditions can affect circuit transient response and stability. Figure 8 shows a kHz, 2nd-order, low-pass filter utilizing the multiple? The components have been selected to provide a maximally-flat Butterworth response.
Beyond the cutoff frequency, roll-off is? The Butterworth response is ideal for applications requiring predictable gain characteristics such as the anti-aliasing filter used ahead of an ADC. Swing-to-Ground R3 ?
VOUT R2 1. Figure 8. If this inversion is not required, or not desired, a noninverting output can be achieved through one of these options: 1 adding an inverting amplifier; 2 adding an additional 2nd-order MFB stage; or 3 using a noninverting filter topology such as the Sallen-Key shown in Figure 9. This software is available as a free download at www. Also, because it is free of the input offset transition characteristics inherent to some rail-to-rail CMOS op amps, the OPA provides low THD and excellent linearity throughout the input voltage swing range.
The amplifier is connected as a unity-gain, noninverting buffer and has an output swing to 0V, making it directly compatible with the ADC minus full-scale input level. A small, signal-switching diode or Schottky diode provides a suitable negative supply voltage of? C3 pF R1 1. R3 k? Figure 9. VIN 0 to 4. IN ADS 16? If a negative power supply is available, this simple circuit creates a? Figure Here, 5? A was used to bias the divider. The resistors must be precise to maintain the ADC gain accuracy.
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