OPT101

8

SBBS002A

www.ti.com

source to sink currents up to approximately 100

µA. The

benefits of this current sink are shown in the typical

10,000pF)” which compare operation with pin 3 grounded

and connected to –15V.

Due to the architecture of this output stage current sink, there

is a slight increase in operating current when there is a voltage

between pin 3 and the output. Depending on the magnitude of

this voltage, the quiescent current will increase by

approximately 100

µA as shown in the typical performance

APPLICATIONS INFORMATION

Figure 1 shows the basic connections required to operate the

OPT101. Applications with high-impedance power supplies

may require decoupling capacitors located close to the

device pins as shown. Output is 7.5mV dc with no light and

increases with increasing illumination.

flux, (in watts) falling on the photodiode. At a wavelength of

approximately 0.45A/W. Responsivity at other wavelengths is

shown in the typical performance curve “Responsivity vs

Wavelength.”

FIGURE 1. Basic Circuit Connections.

The typical performance curve “Output Voltage vs Radiant

Power” shows the response throughout a wide range of

radiant power. The response curve “Output Voltage vs

The OPT101’s voltage output is the product of the photodiode

supply operation. The internal feedback resistor is laser trimmed

to 1M

Ω. Using this resistor, the output voltage responsivity, R

is approximately 0.45V/

µW at 650nm wavelength. Figure 1

shows the basic circuit connections for the OPT101 operating

with a single power supply and using the internal 1M

Ω feedback

resistor for a response of 0.45V/

µW at 650nm. Pin 3 is

connected to common in this configuration.

CAPACITIVE LOADING

The OPT101 is capable of driving load capacitances of 10nF

without instability. However, dynamic performance with

capacitive loads can be improved by applying a negative

bias voltage to Pin 3 (shown in Figure 2). This negative

power supply voltage allows the output to go negative in

response to the reactive effect of a capacitive load. An

internal JFET connected between pin 5 (output) and pin 3

allows the output to sink current. This current sink capability

can also be useful when driving the capacitive inputs of

some analog-to-digital converters which require the signal

NOISE PERFORMANCE

Noise performance of the OPT101 is determined by the op

amp characteristics, feedback components and photodiode

capacitance. The typical performance curve “Output Noise

Voltage vs Measurement Bandwidth” shows how the noise

indicated frequency), when the output voltage minus the

voltage on pin 3 is greater than approximately 50mV. Below

this level, the output stage is powered down, and the effective

bandwidth is decreased. This reduces the noise to

approximately 1/3 the nominal noise value of 300

µVrms, or

100

µVrms. This enables a low level signal to be resolved.

Noise can be reduced by filtering the output with a cutoff

frequency equal to the signal bandwidth. This will improve

signal-to-noise ratio. Also, output noise increases in proportion

to the square root of the feedback resistance, while responsivity

increases linearly with feedback resistance. Best signal-to-noise

ratio is achieved with large feedback resistance. This comes

with the trade-off of decreased bandwidth.

The noise performance of the photodetector is sometimes

characterized by Noise Effective Power (NEP). This is the

radiant power that would produce an output signal equal to the

noise level. NEP has the units of radiant power (watts), or

Watts/

√Hz to convey spectral information about the noise.

The typical performance curve “Noise Effective Power” vs

Measurement Bandwidth" illustrates the NEP for the OPT101.

FIGURE 2. Bipolar Power Supply Circuit Connections.

1M

Ω

OPT101

3pF

2

5

4

V

λ

3

8

V

B

8pF

1

Common

Dark output

≈ 7.5mV

Positive going output

with increased light

0.01 to 0.1

µF

1M

Ω

OPT101

3pF

2

5

4

V

S

λ

3

8

V

B

8pF

1

Common

–V = –1V to (V

0.01 to 0.1

µF

0.01 to 0.1

µF