SELECT - General Inverting and Non-inverting Amplifier Circuit Details

TopologyWelcome to WEBENCH® Amplifier Designer. The first Amplifier Designer page allows you to select an amplifier topology, your power supply requirements and expected temperature range (Figure 1, A). You may notice that there are several topologies available in this tool. However, in this tutorial we will learn how to design inverting and/or non-inverting amplifier circuits.

Figure 1. Amplifier Designer Topology page

There are two general topologies: Non-inverting and Inverting amplifiers. The General Non-inverting Amplifier multiplies the input voltage (Vin) by the

desired positive gain and subtracts a voltage proportional to the applied voltage reference (Vref).

The General Inverting Amplifier multiplies the input voltage (Vin) by the desired negative gain and adds a voltage proportional to the applied voltage reference (Vref).

There are three topologies for the Photodiode Amplifier: Zero Reverse Bias, Negative Reverse Bias and Positive Reverse Bias.

The Zero Reverse Bias Photodiode Amplifier configuration has the Anode and Cathode of the photodiode connecting to the amplifier’s non-inverting input and the reference voltage (Vref).

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The Negative Reverse Bias Photodiode Amplifier configuration has the photodiode anode connecting to a negative bias voltage (Vbias) and the cathode connecting to the amplifier’s non-inverting input and the reference voltage (Vref). The reverse Vbias voltage reduces the photodiode’s junction capacitance.

The Positive Reverse Bias Photodiode Amplifier configuration has the photodiode cathode connecting to a positive bias voltage (Vbias) and the anode connecting to the amplifier’s non-inverting input and the reference voltage (Vref). The reverse Vbias voltage reduces the photodiode’s junction capacitance.

As you select your topology, the software shows the topology’s circuit diagram, mathematical transfer function and a graphical representation of the circuit’s input / output behavior (Figure 1.B). Select the General Inverting Amplifier or General Non-inverting Amplifier button and leave this page by evoking the Start Amplifier Designer button (Figure 1.C) to move onto the Design Requirements view.

Design Requirements

At this point, you will see the Design Requirements area for your circuit design (Figure 2’s section A). With the selected design, you see the circuit diagram details of your topology. Within this page, you will determine your circuit’s power supply (B), input / output voltages (C), loading (F), and bandwidth (G) requirements. This page reflects your entered changes in the DC Transfer Characteristics (E). Your final inputs will provide appropriate information for the Amplifier Designer’s circuit design and the op amp selection.

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Figure 2. General Inverting Design Requirements page

Circuit Diagrams

Figure 3 shows the General Inverting Amplifier and Figure 4 shows the General Non-inverting Amplifier circuit diagrams with the Op Amp, resistors, supply / reference voltages and input signal.

Figure 3. Design Requirements: General Inverting Amplifier topology, from Figure 2’s section A.

The elements in the General Inverting Amplifier circuit are Vin, R1, R2, Vref, Vcc, Vee, Rload and Vterm. Vin represents the circuit’s input signal.

With Vout positioned on top of Rload, the transfer function of this circuit is:

This formula creates a negative going slope with the ratio of R2 and R1. The voltage reference in combination with R2 and R1 create a level shift voltage.

The positive (Vcc) and negative (Vee) power supplies connect directly to the operational amplifier. The output load comprises of Rload and Vterm. Rload is the output load resistance and Vterm is the termination voltage for the output load.

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Figure 4. Design Requirements: General Non-inverting Amplifier topology, from Figure 2’s section A.

The elements in the General Non-inverting Amplifier circuit are Vin, R1, R2, Vref, Vcc, Vee, Rload and Vterm. Vin represents the circuit’s input signal.

With Vout positioned on top of Rload, the transfer function of this circuit is:

This formula creates a positive going slope with the gain formula of (1 + R2 /R1). The voltage reference in combination with R2 and R1 create a negative level shift voltage.

The positive (Vcc) and negative (Vee) power supplies connect directly to the operational amplifier. The output load comprises of Rload and Vterm. Rload is the output load resistance and Vterm is the termination voltage for the output load.

At the start of your design, review these circuits. You then define the input and output values on the Design Requirements page.

Power Supply Specifications

In Figure 2’s section B, you provide details for your power supply requirements (see Figure 5).

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Figure 5. Design Requirements: Desired Power Supply Voltages, from Figure 2’s section B.

If you select the Dual Supply option, you can enter any value into the Vcc and Vee fields as long as Vcc is greater than Vee. For instance, the values of Vee = 97 V and Vcc = 102 V is allowed as long as VinMin, VinMax, VoutMin and VoutMax actual values are between these two power supply voltages (see Input / Output Specifications below). If you select the Single Supply option, Amplifier Designer automatically assigns Vee to zero volts.

Table 1 contains the definitions of the power-supply-voltage fields.

Table 1. Definition of the power supply voltage fieldsDC parameter DefinitionVcc Positive power supply voltage for the op ampVee Negative power supply voltage for the op amp

Assigning power supply voltages is your first step towards the amplifier selection process. Note that it is possible that there will be no amplifiers found for your circuit if (Vcc-Vee) is too small or too large.

Input / Output Specifications

In Figure 2’s section C, you define your circuit’s input, output and reference voltages. You can program your desired voltages with one of the four techniques (Figure 6, 7, 8, 9) to match the input style to your preference.

Figure 6. Design Requirements: Desired Input and Output Requirements, Input Voltage Limits, Output Voltage Limits, from Figure 2’s section C.

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The selected first button (Figure 2’s section C and Figure 6) allows you to choose the input and output voltage limits. From your inputs, Amplifier Designer determines the circuit gain as well as the appropriate value for the voltage reference (Vref).

Figure 7. Design Requirements: Desired Input and Output Requirements, Input Voltage Limits, Gain, from Figure 2’s section C.

The selected second button (Figure 2’s section C and Figure 7) allows you to program the maximum and minimum input voltages and circuit gain. From your inputs, Amplifier Designer will determine the appropriate values for the maximum and minimum output voltages, as well as the value of the voltage reference (Vref). In this view, you can adjust the value of Vref.

Figure 8. Design Requirements: Desired Input and Output Requirements, Input Voltage Range, Output Voltage Range, from Figure 2’s section C.

The selected third button (Figure 2’s section C and Figure 8) allows you to program the input and output voltage ranges. Additionally, the Amplifier Designer requires the assignments of the input and output midpoint voltages. From your inputs, Amplifier Designer will determine the appropriate values for the maximum and minimum input and output voltages, as well as the appropriate value for the voltage reference (Vref).

The selection in Figure 8 offers an effective way to design amplifier circuits with multiple power-supply requirements. For instance, consider the design input/output configuration of a dual supply amplifier in combination with a single supply analog-to-digital converter

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(ADC). In this instance, the amplifier power is +/- 5V and the ADC power is 5 V. Figure 9 shows this configuration.

Figure 9. Design Requirements: Desired Input and Output Requirements, Input Voltage Range, Output Voltage Range, from Figure 2’s section C.

Consider the amplifier’s Vin pk-pk to equal 1V with Vin midpoint equaling 0 V. For the amplifier output, Vout pk-pk equals to 4 V and the Vout midpoint is 2.5 V. Table 2 shows the resulting Amplifier Designer voltages.

Table 2. Input / Output parameters and their definitionsINPUT OUTPUT

Vin Min: -0.5 V Vout Min: 0.5 VVin Max: 0.5 V Vout Max: 4.5 V

Vin pk-pk: 1 V Vout pk-pk: 4 VVin Midpoint: 0 V Vout Midpoint: 2.5 V

Closed Loop Gain: 4 V/V Vref: -0.833 V

In Table 2, the input column pertains to the amplifier input at Vin. The output column describes the output voltages of the amplifier as well as the input voltage to the ADC.

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Figure 10. Design Requirements: Desired Input and Output Requirements, Input Voltage Range, Gain, from Figure 2’s section C.

The selected fourth button (Figure 2’s section C and Figure 10) allows you to program the input voltage range, input midpoint voltage, circuit gain, and an opportunity to select the value of the reference voltage (Vref). From your inputs, Amplifier Designer will determine the appropriate values for the maximum and minimum input and output voltages.

Of these four choices (Figure 6, 7, 8, 9), select your most comfortable style. Be aware that there is no “crosstalk” between these techniques; so find the one you like and stay with it.

Figure 2’s section D summaries the voltages and gains from your selections in Figure 2’s section C. Figure 11 shows a zoom-in of Figure 2’s section D. As Figure 11 shows, you will receive ten critical voltage and gain values that reflect your circuit design.

Figure 11. Design Requirements: Summary of selected voltages and gain from section Figure 2’s section D.

Table 3 contains the definitions of the input, output, gain and voltage reference fields.

Table 3. Input / Output parameters and their definitionsDC parameter DefinitionVin Min The Vin source’s minimum input voltage value.Vin Max The Vin source’s maximum input voltage value.Vin Range Source’s (Vin) voltage range. This range equals Vin Max – Vin

Min.Vin Midpoint Source’s (Vin) midpoint voltage. This value equals (Vin Max + Vin

Min)/2.Vout Min The minimum voltage that occurs at the output of the Op Amp.

This voltage occurs at the top of load resistor, Rload. Amplifier Designer recommends op amps that are able to linearly swing to the Vout Min value.

Vout Max The maximum voltage that occurs at the output of the Op Amp. This voltage occurs at the top of load resistor, Rload. Amplifier Designer recommends op amps that are able to linearly swing to the Vout Max value.

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Vout Range Amplifier’s (Vout) output voltage range. This range equals Vout Max – Vout Min

Vout Midpoint Amplifier’s (Vout) midpoint output voltage. This value equals (Vout Max + Vout Min)/2

Closed Loop Gain

The closed loop gain of the General Inverting amplifier is equal to –(VoutMax-VoutMin)/(VinMax-VinMin). The closed loop gain of the General Non-inverting amplifier is equal to (1 + R2/R1) (VoutMax-VoutMin)/(VinMax-VinMin)

Recommended Vref

Amplifier Designer recommends a voltage reference value to insure that the amplifier output voltage minimum and maximum is achievable given the amplifier minimum and maximum input voltage

DC Transfer Characteristic

The DC performance graph (Figure 2’s section E and Figure 12 and 12) reflects the values in the Input / Output Requirements section (Figure 2’s section C). In Figure 12 and 12, the y-axis maps the output range and the x-axis maps the input range of the General Inverting Amplifier or General Non-inverting Amplifier circuits.

Figure 12. Design Requirements: General Inverting Amplifier DC Transfer Characteristic: Summary of selected voltages and gain from section Figure 2’s section B.

Figure 12 shows the graphical DC input versus output transfer function of a General Inverting amplifier circuit. Note that the curve’s slope is negative.

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Figure 13. Design Requirements: General Non-inverting Amplifier DC Transfer Characteristic: Summary of selected voltages and gain from section, Figure 2’s section C.

Figure 13 shows the graphical DC input to output of a General Non-inverting amplifier circuit. Note that the curve’s slope is positive

Figure 12 and 13 are dynamic graphs, which change as you update your inputs in Figure 2’s section C.

Output Load

Amplifier Designer uses the Output Load values (Figure 2’s section F) to select amplifiers that perform in their linear region, given the Vout Min and Vout Max requirements. You can elect to input Output Current or Resistive Load values as you enter the output current requirements. Either way, Amplifier Designer will use the inputted values to insure that the selected amplifiers operate in their linear region, as long as the output remains between Vout Max and Vout Min.

If you click on the Output Current button (Figure 2’s section F and Figure 14), you be able to change Max Sink and Max Source current values.

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Figure 14. Design Requirements: Summary of selected voltages and gain from section Figure 2’s section F.

The Max Sink and Max Source values quantify the amount of amperes the amplifier needs to be able to sink or source to your load. These two values can be the same or different.

If you click on the Resistive Load button (Figure 2’s section F and Figure 15), you configure the value of your load resistor and its termination voltage.

Figure 15. Design Requirements: Summary of selected voltages and gain from section Figure 2’s section F.

Table 4 contains the definitions of the output load fields.

Table 4. Load conditions and their definitions DC parameter DefinitionVterm The termination voltage for the load resistor, R load

Max Sink Maximum sink amplifier output current. Amplifier Designer uses this value to insure that the amplifier operates in its linear region as long as the output remains between Vout Max and Vout Min

Max Source Maximum source amplifier output current. Amplifier Designer uses this value to insure that the amplifier operates in its linear region as long as the output remains between Vout Max and Vout Min

Load Resistive load (Rload) on the output of the Op amp. Amplifier Designer uses Rload in combination with Vterm to determine the values of Max Sink and Max Source output currents. This tool uses these values to insure that the recommended amplifiers operate in their linear regions as long as the output remains between Vout Max and Vout Min.

Vterm The termination voltage (Vterm) is on the bottom side of R load. Amplifier Designer uses Rload in combination with Vterm to

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determine the values of Max Sink and Max Source output currents. This tool uses these values to insure that the recommended amplifiers operate in their linear regions as long as the output remains between Vout Max and Vout Min.

Closed Loop Bandwidth / Slew Rate

Amplifier Designer uses the Closed Loop Bandwidth/Slew Rate values to select amplifiers that perform the given frequency range or speed. You can elect to input your desired bandwidth (Full Power or Small Signal) or target your desired system Slew Rate by selecting the appropriate button and entering your desired value. Either way, Amplifier Designer will use the inputted values to insure that the selected amplifiers operate at the speed or frequency equal to or greater than the entered values in these fields.

If you click on the Output Current button (Figure 2’s section F and Figure 16), you will see where you can input either Full Power or Small Signal frequency value.

Figure 16. Design Requirements: Summary of selected voltages and gain from section Figure 2’s section F.

If you select the Full Power button (Figure 16), Amplifier Designer will recommend op amps for your circuit that are capable to produce a full-scale sinusoidal signal equal to your entered frequency value. It is possible that Amplifier Designer’s recommended amplifiers will exceed this entered frequency value.

The Full Power Bandwidth is the frequency at which an output sinusoid, with amplitude equal (VoutMax-VoutMin), begins to show distortion due to slew-rate.

Figure 17. Design Requirements: Summary of selected voltages and gain from section Figure 2’s section F.

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If you select the Small Signal button (Figure 17), Amplifier Designer will recommend op amps for your circuit that are capable to produce sinusoidal signals equal +/- 100 mV sinusoidal signal at Vout Midpoint operation without magnitude degradation at frequencies equal to your entered frequency value. It is possible that Amplifier Designer’s recommended amplifiers will exceed this entered frequency value.

Figure 18. Design Requirements: Summary of selected voltages and gain from section Figure 2’s section F.

If you select the Slew Rate button (Figure 18), Amplifier Designer will recommend op amps for your circuit that are capable of slewing at the entered slew rate value or faster. It is possible that Amplifier Designer’s recommended amplifiers will exceed this entered system slew rate value.

Table 5 contains the definitions of the AC input fields.

Table 5: AC parameters and their definitionsAC parameter Definition

Full Power

Amplifier Designer recommends op amps where the General Inverting amplifier’s Full Power Bandwidth performs Vout Max to Vout Min operation without magnitude degradation at frequencies at least equal to the specified Full Power Bandwidth.

Small Signal

Amplifier Designer recommends op amps where the General Inverting amplifier’s Small Signal Bandwidth performs with a +/- 100 mV sinusoidal signal at Vout Midpoint operation without magnitude degradation at frequencies at least equal to the specified Small Signal Bandwidth

Slew RateAmplifier Designer recommends op amps where the General Inverting amplifier system has a slew rate at least equal to the value provided.

As you complete the fields in the Design Requirements page, the software shows the theoretical DC performance in the Input / Output segment (Figure 2’s section D and Figure 11) and in the graphs, (Figure 2’s section E and Figures 11 and 12). Before you leave this page, make sure that your inputs are accurate. Your final inputs will provide appropriate information for the circuit design and op amp selection. Upon completion,

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you can leave this page by evoking the Create Amplifier Design button (Figure 2’s section H) to move onto the Visualizer view.

Visualizer

In the Amplifier Designer Visualizer, you continue to select your circuit amplifier. There are several opportunities to sort and reduce the provided list on this page (Figure 19).

Figure 19. Visualizer: (A) Design Criteria, (B) Optimizer, Refine Results and (C) Solutions Table

Design Criteria, Schematic and Components Circuit

At the top of this view, there is a summary of your circuit design criteria, schematic, and the value of the components (Figure 19’s section A and Figure 20).

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A B

C

Figure 20. Amplifier Designer Visualizer: Design Criteria, Schematic and Components view from section Figure 19’s section A.

In Figure 20, the Design Criteria box (A) provides the basics of the circuit including the desired Source’s (Vin) input range, amplifier output range, closed loop gain, voltage reference value and closed loop bandwidth. The Schematic view (B) shows you the location of the components. The Components view (C) provides the Operational amplifier name and actual (ideal) resistor values.

Optimizer and Refine Results

Also at the top of this view in Figure 19’s section B, there are the Optimizer and Refine Results sections (Figure 19’s section B and Figure 20).

Figure 20. Amplifier Designer Visualizer: Optimizer view, from Figure 19’s section B.

Figure 20 shows that the Optimizer contains there pull-down boxes. All three of these selection boxes contain Precision, Noise, Temp Drift, Supply Current, and Cost parameters. The three pull-down boxes are weighted as Very Important ~ 0.54, Important ~ 0.3 and Less Important ~ 0.16. As you select your parameters for each box, the Solutions Table below resorts according to your Optimizer settings.

Amplifier Designer’s Inverting and Non-inverting site offers further sorting in the Refine Results view (Figure 19’s section B and Figure 22).

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Figure 22. Amplifier Designer: Refine Results, from Figure 19’s section B.

In the Refine Results view, you are able to select your preferred package type, the number of amplifier channels and amplifiers with shutdown pins.

Selections in this area reduce your amplifier list in the solution table.

Solutions Table

The amplifiers in the Solutions Table (Figure 19’s section C and Figure 23) perform correctly per your Design Requirements inputs. Your Optimizer and Refine Results selections (Figure 19’s section B, Figure 20 and Figure 22) initiate a re-sort of the amplifiers in the Solutions table.

Figure 23. Amplifier Designer Visualizer: Solutions Table from section Figure 19’s section C.

Several features go beyond the Optimizer and Refine Results capability. In the upper left corner of the table (Figure 23, red square), there is a field that allows you to search for your favorite amplifier. Further to the right, you can see the total number of amplifiers available in the table. As a final option, you can click on any column (Figure 23, blue square) which sorts the amplifier members according to that column. The column sorting overrides your Optimizer selections.

Table 6 provides the Solutions Table column definitions.

Table 6. Solutions Table column definitions

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Column DefinitionPart Orderable part numberCreate Click to carry selected amplifier to the Designer Summary pageSimulation Amplifier Designer is able to perform a TI-Spice Simulation within

WEBENCH if the symbol existsPackage Amplifier package. To refine your package selection, use the Refine

Results windowAmplifier Bandwidth (MHz)

Gain Bandwidth Product of the amplifier (GBWP)

Small Signal Bandwidth (MHz)

GBWP / Closed Loop Noise Gain

Full-Scale Bandwidth (kHz)

Equals Slew Rate / (2 * (Vcc – Vee))

Output DC Error (typ mV)

Calculated root-sum-square combination of voltage offset, bias current, current offset, and common-mode rejection.

Total Output Noise (uVrms)

Once standard deviation of noise. Includes amplifier and the resistor (R1 and R2) noise.

Output Temperature Delta (typ, mV)

Includes the amplifier input offset voltage and input bias current drifts

IC Supply Current (mA)

Maximum quiescent supply current per amplifier

Output Offset (mV)

Equals Gain * offset voltage

Max Power supply (V)

Maximum specified amplifier power supply

Min Power supply (V)

Minimum specified amplifier power supply

1k Price (USD)

Amplifier 1000 piece budgetary pricing

In the Visualizer view, you have further refined your inputs. You may be interested in

performing simulations with your circuit. If so, makes sure the device has a symbol in the Solutions Table’s Simulation column. At this point, you select your circuit’s amplifier by clicking on the associated Open Design button.

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