Precision Rectifier Symbol
Definition: The Precision Rectifier symbol represents an op-amp-based circuit that rectifies AC signals to DC with near-zero forward-voltage drop, overcoming the 0.6 V diode threshold that limits conventional rectifier circuits, as used in instrumentation and signal-processing designs compliant with IEEE 315-1975 functional block notation.
Also known as: superdiode, absolute value circuit, ideal rectifier, op-amp rectifier.
What the Precision Rectifier symbol means
The Precision Rectifier symbol denotes a functional block that converts an alternating or bipolar input signal into a unipolar output with the same magnitude, using an operational amplifier and one or more diodes within its feedback loop to eliminate the forward-voltage drop of the diodes.
In circuit diagrams the precision rectifier block is used wherever accurate, low-level AC-to-DC conversion is required, such as in audio peak detectors, AC voltmeters, signal demodulators, and control systems where the 0.6 V diode drop would introduce unacceptable error at millivolt-level signals.
How to identify the Precision Rectifier symbol
The precision rectifier symbol is drawn as a triangular amplifier body (pointing right) with an input line entering the left vertex and an output line leaving the right vertex, identical to a standard op-amp or buffer block. A small diode symbol or arrow annotation near the output or inside the triangle distinguishes it from a plain buffer or comparator. Some schematic tools label the block 'PR' or 'ABS', while others show the full op-amp triangle with an explicit diode in the feedback path drawn alongside.
Function and usage boundary
The precision rectifier uses an operational amplifier to place one or more rectifying diodes inside its feedback loop, so that the op-amp's high open-loop gain forces the output to track the input with zero effective diode drop. For positive half-cycles the output follows the input exactly; for negative half-cycles the output is clamped to zero (half-wave) or inverted and summed to produce the absolute value (full-wave). The result is accurate rectification of signals as small as a few millivolts, far below the 0.6 V threshold that defeats passive diode rectifiers.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 does not define a dedicated symbol for the precision rectifier; it is represented as a general amplifier block (IEC 60617-13) with an annotation indicating rectification function. |
|---|---|
| ANSI/IEEE 315 | IEEE 315-1975 (ANSI Y32.2) treats the precision rectifier as a functional amplifier block symbol; the triangle represents the amplifying element and any diode annotation within or adjacent to the block identifies the rectification function. |
| Key difference | Both IEC and ANSI/IEEE use a triangle for the amplifier body; neither standard provides a unique dedicated glyph for the precision rectifier, so representation is identical in both traditions. |
The displayed SVG is the live editor implementation, not a licensed reproduction or certification of an IEC or IEEE database glyph. Verify the exact official entry and project edition before issuing work.
Logical terminals
| Logical ID | Editor terminal name |
|---|---|
| in | In |
| out | Out |
Where the Precision Rectifier symbol is used
- AC voltmeters and true-RMS measurement circuits requiring rectification of millivolt-level signals
- Audio peak detectors and envelope followers in signal processors
- AM demodulators where carrier amplitude must be recovered with high accuracy
- Current-sensing circuits that convert a bipolar shunt voltage to a unipolar ADC input
- PID controllers with absolute-value feedback for motor positioning systems
- Biomedical instrumentation amplifiers rectifying ECG or EMG waveforms for envelope extraction
Key facts
- A precision rectifier (superdiode) uses an op-amp with a diode in its feedback loop to achieve rectification with an effective forward voltage drop of nearly 0 V, compared with 0.6 V for a silicon diode alone.
- The precision rectifier symbol in schematics is a triangular amplifier block (IEEE 315-1975) sometimes annotated with a small diode symbol or labelled 'PR' or 'ABS' to indicate its function.
- Half-wave precision rectifiers pass only one polarity of the input; full-wave (absolute-value) configurations combine two op-amp stages to produce |Vin| at the output for both polarities.
- The upper operating frequency of a precision rectifier is limited by the op-amp's slew rate and gain-bandwidth product; fast op-amps (e.g. LM318, AD711) extend useful range to hundreds of kilohertz.
- The circuit has two pins in schematic representation: In (signal input) and Out (rectified output); power supply rails are implied by the op-amp symbol.
- Precision rectifiers are used in true-RMS converters, peak detectors, and absolute-value circuits in instrumentation, audio, and control engineering.
- Unlike a passive diode rectifier, a precision rectifier maintains output accuracy for input signals smaller than the op-amp's offset voltage, which is typically less than 1 mV for precision op-amps.
Frequently asked questions
What does the precision rectifier symbol mean in a circuit diagram?
The precision rectifier symbol represents an op-amp-based block that converts an AC or bipolar signal to a unipolar (rectified) output with negligible forward-voltage error. It indicates that the circuit performs ideal or near-ideal rectification suitable for small-signal measurement applications.
What does the precision rectifier symbol look like?
The precision rectifier symbol appears as a rightward-pointing triangle (the standard op-amp or amplifier block shape) with an input on the left and an output on the right, often annotated with a small diode arrow near the output or inside the triangle, and sometimes labelled 'PR' or 'ABS'.
What is the difference between a precision rectifier and a normal diode rectifier?
A normal diode rectifier drops approximately 0.6 V across the diode, which causes large errors when rectifying millivolt-level signals. A precision rectifier places the diode inside the op-amp's feedback loop, reducing the effective forward drop to microvolts and enabling accurate rectification of very small signals.
What is a superdiode?
A superdiode is an informal name for the precision rectifier circuit. It describes an op-amp and diode combination that behaves like an ideal diode with zero forward-voltage drop and infinite reverse resistance, making it suitable for rectifying low-amplitude signals.
What standard defines the precision rectifier symbol?
IEEE 315-1975 (ANSI Y32.2) defines the general amplifier block triangle used to represent the precision rectifier in schematics. IEC 60617-13 covers amplifier symbols similarly. Neither standard defines a unique glyph specifically for the precision rectifier; the diode annotation distinguishes it.
What are the pins of a precision rectifier block in a schematic?
The schematic block shows two signal pins: In (the AC or bipolar input signal) and Out (the rectified unipolar output). Op-amp supply rails (VCC and GND or V+ and V-) are typically shown on the underlying op-amp symbol when the internal circuit is expanded.
What is the designator letter for a precision rectifier?
There is no universally standardised single-letter designator for a precision rectifier block. In practice, the block is labelled U (for a general IC or functional block) or annotated with 'PR' or 'ABS' to indicate its function within a larger schematic.
Related symbols
- Differential Amplifier symbol
- Op-Amp symbol
- Op-Amp (DIP) symbol
- Peak Detector symbol
- Summing Amplifier symbol
- Transimpedance Amplifier symbol
Physical breadboard, PCB, and panel mapping
No universal physical profile is published for this symbol yet. Create a versioned custom part from the exact manufacturer dimensions and terminal map before fabrication.
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