SBOS841A November 2016 – January 2017 OPA2316-Q1 , OPA316-Q1 , OPA4316-Q1

PRODUCTION DATA.

- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Detailed Description
- 8 Application and Implementation
- 9 Power Supply Recommendations
- 10Layout
- 11Device and Documentation Support
- 12Mechanical, Packaging, and Orderable Information

- PW|14

- PW|14

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

When receiving low-level signals, the device often requires limiting the bandwidth of the incoming signals into the system. The simplest way to establish this limited bandwidth is to place an RC filter at the noninverting pin of the amplifier, as Figure 39 shows.

If even more attenuation is needed, the device requires a multiple-pole filter. The Sallen-Key filter can be used for this task, as Figure 40 shows. For best results, the amplifier must have a bandwidth that is eight to 10 times the filter frequency bandwidth. Failure to follow this guideline can result in phase shift of the amplifier.

Some applications require differential signals. Figure 41 shows a simple circuit to convert a single-ended input of 0.1 V to 2.4 V into a differential output of ±2.3 V on a single 2.7-V supply. The output range is intentionally limited to maximize linearity. The circuit is composed of two amplifiers. One amplifier functions as a buffer and creates a voltage (V_{OUT+}). The second amplifier inverts the input and adds a reference voltage to generate V_{OUT–}. V_{OUT+} and V_{OUT–} range from 0.1 V to 2.4 V. The difference (V_{DIFF}) is the difference between V_{OUT+} and V_{OUT– }, resulting in a differential output voltage range of 2.3 V.

Table 1 lists the design requirements:

DESIGN PARAMETER | VALUE |
---|---|

Supply voltage | 2.7 V |

Reference voltage | 2.5 V |

Input voltage | 0.1 V to 2.4 V |

Output differential voltage | ±2.3 V |

Output common-mode voltage | 1.25 V |

Small-signal bandwidth | 5 MHz |

The circuit in Figure 41 takes a single-ended input signal (V_{IN}) and generates two output signals (V_{OUT+} and V_{OUT–}) using two amplifiers and a reference voltage (V_{REF}). V_{OUT+} is the output of the first amplifier and is a buffered version of the input signal (V_{IN}) , as shown in Equation 1. V_{OUT–} is the output of the second amplifier that uses V_{REF} to add an offset voltage to V_{IN} and feedback to add inverting gain. The transfer function for V_{OUT–} is given in Equation 2.

Equation 1.

Equation 2.

The differential output signal (V_{DIFF}) is the difference between the two single-ended output signals (V_{OUT+} and V_{OUT–}). Equation 3 shows the transfer function for V_{DIFF}. Using conditions in Equation 4 and Equation 5 and applying the conditions that R_{1} = R_{2} and R_{3} = R_{4}, the transfer function is simplified into Equation 6. Using this configuration, the maximum input signal is equal to the reference voltage, and the maximum output of each amplifier is equal to V_{REF}. The differential output range is 2 × V_{REF}. Furthermore, the common-mode voltage is one half of V_{REF}, as shown in Equation 7.

Equation 3.

Equation 4.

Equation 5.

Equation 6.

Equation 7.

Linearity over the input range is key for good dc accuracy. The common-mode input range and output swing limitations determine the linearity. In general, an amplifier with rail-to-rail input and output swing is required. Bandwidth is a key concern for this design, so the OPAx316-Q1 is selected because the bandwidth is greater than the target of 5 MHz. The bandwidth and power ratio makes this device power efficient and the low offset and drift ensure good accuracy for moderate precision applications.

Because the transfer function of V_{OUT–} is heavily reliant on resistors (R_{1}, R_{2}, R_{3}, and R_{4}), use resistors with low tolerances to maximize performance and minimize error. This design uses resistors with resistance values of 49.9-kΩ and tolerances of 0.1%. However, if the noise of the system is a key parameter, smaller resistance values (6-kΩ or lower) can be selected to keep the overall system noise low. This ensures that the noise from the resistors is lower than the amplifier noise.

The measured transfer functions in Figure 42, Figure 43, and Figure 44 are generated by sweeping the input voltage from 0.1 V to 2.4 V. The full input range is actually 0 V to 2.5 V, but is restricted to 0.1 V to maintain optimal linearity. For more details on this design and other alternative devices that can be used in place of the OPAx316-Q1, see *Single-Ended Input to Differential Output Conversion Circuit Reference Design*.