SBOT053 April   2025 OPA607 , OPA814 , OPA836 , THS4531A , THS4551 , THS4561 , THS4567

 

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Example: Optical Motor Encoder Block Diagram with Discrete and Integrated SolutionsExample: Optical Motor Encoder Block Diagram with Discrete and Integrated Solutions

What are the Key Specifications for Transimpedance Amplifiers (TIA) in Motor Encoders?

  • Gain-Bandwidth Product: The signal-chain bandwidth required by the encoder is determined by the resolution (periods per revolution) and speed (revolutions per minute). The wider the signal-chain bandwidth, the larger the gain-bandwidth product needed to maintain linearity across a wide range of gain values.
  • Offset Voltage and Input Bias Current: A higher precision amplifier improves total dynamic range received from the output of the photodiode. The smaller the output current value that is detectable from the photodiode, the more precise the motor encoder positioning.
  • Voltage Noise and Total Harmonic Distortion: Lower noise and distortion performance amplifiers enable maximum performance of the selected ADC. For more information on ADC selection, see Precision ADCs for Motor Encoders and Position Sensing.
  • Size: Encoders are typically located on a PCB mounted on the motor; therefore, a small form factor amplifier is required.

What are the Key Specifications for Fully Differential Amplifiers (TIA) in Motor Encoders?

  • Fully Differential Architecture: A fully-differential amplifier allows the input signal to be converted into a differential signal if using a single ended transimpedance amplifier in an optical path, or remain a fully-differential signal while setting the output common mode voltage if a TIA is not required.
  • High Gain-Bandwidth Product: Add additional gain and active filtering onto the amplifier while maintaining signal-chain bandwidth linearity.
  • Low Offset Voltage and Drift: Improve precision performance for minimal DC shift impact on the system.
  • Rail to Rail Output: Maximize the full scale range available on the output to maintain signal integrity.

Need additional assistance? Ask our engineers a question on the TI E2E™ Amplifiers Support Forum.

Recommended Discrete Components

Table 1 Transimpedance Amplifier (TIA)
ParameterOPA607OPA836OPA814

Supply Voltage Range (V)

2.2 - 5.5

2.5 - 5.5

6 - 12.6

Gain Bandwidth Product (MHz)

50

118

250

Quiescent Current, IQ (typ) (mA)

0.9

1

16

Slew Rate (typ) (V/µs)

24

560

750

Rail-to-Rail

In to V-, Out

In to V-, Out

No

Input Offset Voltage, VOS (max) (mV)

0.6

0.4

0.25

Offset Voltage Drift (typ) (µV/oC)

0.3

1.1

1

Voltage Noise at Flatband (typ) (nV/√Hz)

3.8

4.6

5.3

Operating Temperature Range (oC)

-40 to 125

-40 to 125

-40 to 85

Channel Count Variants

OPA2607

OPA2836

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Table 2 Fully Differential Amplifier (FDA)

Parameter

THS4531A

THS4561

THS4551

Supply Voltage Range (V)

2.5 - 5.5

2.85 - 12.6

2.7 - 5.4

Gain Bandwidth Product (MHz)

27

60

135

Quiescent Current, IQ (typ) (mA)

0.25

0.78

1.35

Slew Rate (typ) (V/µs)

220

230

220

Rail-to-Rail

In to V-, Out

In to V-, Out

In to V-, Out

Input Offset Voltage, VOS (max) (mV)

00.4

0.25

0.175

Offset Voltage Drift (typ) (µV/oC)

3

0.5

0.45

Voltage Noise at Flatband (typ) (nV/√Hz)

10

4

3.3

Operating Temperature Range (oC)

-40 to 125

-40 to 125

-40 to 125

Recommended Integrated Components

Table 3 Integrated Differential TIA + ADC Driver
ParameterTHS4567
Supply Voltage Range (V)3.3 -6
Gain Bandwidth Product (MHz)220
Quiescent Current, IQ (typ) (mA)2
Slew Rate (typ) (V/µs)500
Rail-to-RailOut
Input Bias Current, IBIAS (max) (pV)750
Input Offset Voltage, VOS (max) (mV)10
Offset Voltage Drift (typ) (µV/oC)1
Voltage Noise at Flatband (typ) (nV/√Hz)4.2
Operating Temperature Range (oC)-40 to 125
FeaturesIndependent input and output common mode control, shutdown