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OPA659

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SBOS342C – DECEMBER 2008 – REVISED NOVEMBER 2015

8 Detailed Description

8.1 Overview

The OPA659 is high gain-bandwidth, voltage feedback operational amplifier featuring a low noise JFET input

stage. The OPA659 is compensated to be unity gain stable. The OPA659 finds wide use in optical front-end

applications and in test and measurement systems that require high input impedance.

8.2 Feature Description

8.2.1 Input and ESD Protection

The OPA659 is built using a very high-speed complementary bipolar process. The internal junction breakdown

voltages are relatively low for these very small geometry devices. These breakdowns are reflected in the

Absolute Maximum Ratings table. All device pins are protected with internal ESD protection diodes to the power

supplies, as Figure 34 shows.

Figure 34. Internal ESD Protection

These diodes provide moderate protection to input overdrive voltages above the supplies as well. The protection

diodes can typically support 30-mA continuous current. Where higher currents are possible (for example, in

systems with ±12-V supply parts driving into the OPA659), current limiting series resistors should be added into

the two inputs. Keep these resistor values as low as possible because high values degrade both noise

performance and frequency response.

8.3 Device Functional Modes

8.3.1 Split-Supply Operation (±3.5 V to ±6.5 V)

To facilitate testing with common lab equipment, the OPA659 may be configured to allow for split-supply

operation. This configuration eases lab testing because the mid-point between the power rails is ground, and

most signal generators, network analyzers, oscilloscopes, spectrum analyzers and other lab equipment reference

their inputs and outputs to ground. Figure 36 and Figure 37 show the OPA659 configured in a simple

noninverting and inverting configuration respectively with ±6-V supplies. The input and output will swing

symmetrically around ground. Due to its ease of use, split-supply operation is preferred in systems where signals

swing around ground, but it requires generation of two supply rails.

8.3.2 Single-Supply Operation (7 V to 13 V)

Many newer systems use single power supply to improve efficiency and reduce the cost of the extra power

supply. The OPA659 is designed for use with split-supply configuration; however, it can be used with a single-

supply with no change in performance, as long as the input and output are biased within the linear operation of

the device. To change the circuit from split supply to single supply, level shift all the voltages by 1/2 the

difference between the power supply rails. An additional advantage of configuring an amplifier for single-supply

operation is that the effects of –PSRR will be minimized because the low supply rail has been grounded.

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