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Is there a way to simulate different user skin tones?


People with darker skin will absorb more incident light, so the reflected light is weaker. Due to the fact that skin, tissues and veins do not change in volume with heart beat at a steady state, the intensity of the absorbed light and reflected light is stable, converted to direct current (DC) through a photodetector (PD). Therefore, if the simulator can emit different intensity LED light, then it can achieve the goal to simulate different user skin tones. AECG100’s PPG module provides users to adjust different DC levels to emit different LED intensities.


At the same time, arterial blood volume changes when heart beats. We can refer the arterial blood volume change as an alternating current (AC) signal comparing to the larger DC signal. AECG100 also provides the capability to allow users to adjust the AC level to simulate different arterial blood volume.


Is there a way to simulate different ambient light conditions (indoors/outdoors)?

AECG100 cannot simulate different ambient light conditions at this version. Alternatively, AECG100 has data playback function, which offers users to record their self-collected waveform with different ambient light conditions and then play these recorded waveforms back from AECG100 to simulate such condition.

Does the AECG emission light reflect the different LED intensity variations of the DUT?

After setting properly, AECG is a fixed intensity output, and the output intensity does not support the corresponding DUT LED intensity change.

Why there are no responses during test? (Position)

The first possibility is the position between AECG100 and DUT. Or to be more specific, the DUT’ LED and the tester’s PD are not talking to each other due to position problems. Here are some examples:



Because of the LED emission range and mechanism issues, it may be necessary to adjust the DUT location to the position where the signals can be seen.

Why there are no responses during test? (Trigger Level)

AECG100 Trigger level is the threshold level to trigger AECG LED on (emit the light), through a LED switch to control AECG LED on/off. If trigger Level over DUT LED signal range, it will induce AECG LED not to emit the light. If it’s under the range, it will induce AECG LED always emit the light (become CW mode). Both conditions will make the DUT have no responses to AECG LED behaviors. Therefore, the appropriate trigger level is important for some no respond conditions. Please refer to the table below:



Will DUT reflection light or outside ambient light induce interference?

As shown above:

Blue arrow represents the DUT reflection light or outside ambient light which be reflected by AECG100 mechanism.

Red arrow represents AECG100 LED emit light (DC part)

Pink arrow represents AECG100 LED emit light (AC part)

Therefore, the light received by DUT PD can be simply as shown in the following figure (the AC/DC amplitude is not proportional, actual AC amplitude is much smaller than DC amplitude).



If the blue area is very small (compared to the red area) or is constant (predictable level and can be deducted from the red area), which will not cause interference.

When the application is single color light (such as green light), DC is a fixed value and the blue part is not deducted from the application. It doesn’t affect the test too much.

SpO2 value is related to the ratio of R(PI)/IR(PI), PI= AC/DC, for different wavelengths of light and mechanism, the ratio of the red to the blue area is different, so it can't make the blue area small enough to ignore it (isolate the reflection light), or to be able to accurately deduct the predictable level in advance, will cause a large error in SpO2 calculation.

DUT sampling method introduction

As shown in the above figure, the DUT will light during the sample interval. The sample wave in the above picture maybe is a group pulse of each time interval (one pulse or more pulses)

The above figure shows that the sampling group at each sample interval subdivided to 3 pulses. Taking a single green light as an example, the pulse may be a switch from a different position LED, and the LED intensity of each switch is not necessarily the same. After sampling, take which group to calculate will base on the algorithm of each DUT.

Take SpO2 (R/IR) testing as an example, AECG LED ON/OFF is based on the Sampling Pulse Timing of DUT. As the electrical circuit would have response delay and DUT's Red LED and IR LED normally would turn on in sequence, AECG100 will determine to emit the corresponding LED signals right after the detection of DUT's optical signals. 

The above figure shows that how to take the sample data (RAW data) and the ways to calculate the sample values. The red diagonal line is the area where there is no light, A and A' are the sample values when the light is turned off, and B is the sampled value received after the light is turned on. Currently, most of the above two algorithms are used as sampling RAW Data. The A point is best taken before lighting, and the B point is best after the LED is stable and before turning off the light, A' is best to sample after the light is turned off and stable, this time point may pay special attention, DUT LED may not be extinguished immediately (A or (A+A')/2 is regarded as the background value of ambient light or noise...).

Can the wavelength of the light source be customized?

It may possible, the biggest problem with different wavelengths is the testing standards and processes, each different wavelength LEDs may require us to prepare a set of testing standards, which may require extra effort and cost at the moment.

DUT LED light intensity detect

Currently, HRS/AECG PPG series can detect the light intensity through ADC of PD, but with some limits to display the detective values, for example, when LED light is too strong or too weak, or the light pulse duration is too short. In this case, please connect the signal directly to the oscilloscope and observe the value received by the PD from the oscilloscope.

If DUT only has PPG to measure the Heart Rate, then just purchase HRS200 is enough, don’t need to buy AECG?

If there is no requirement of ECG or SpO2 development, only HRS200 is enough.

AECG can output PPG/ECG signal to DUT, can AECG help to verify whether the PWTT calculated by the DUT is correct or not?

Yes, AECG can control the time difference between PPG and ECG signal, this function can help DUT to verify the PWTT accuracy.

When replacing the light source module, the operating software must also be replaced?

No, it is currently in the same operating software, but the operating software will detect the difference of the module, automatically set the different operation screens.

How to overcome the impact of ambient light on PPG testing?

Shading, light blocking, need DUT to deal with the mechanism

The PPG function difference between AECG and HRS200?

AECG has more function as follows:

(1) Support SpO2

(2) More waveform parameters setup

(3) More PD Sample Rate

(4) Software control LED maximum light intensity (shipping SW only)

(5) SW control trigger level

How PPG simulator simulate the different color of skin?

Can simulate skin color by control the DC value of PPG simulator, but the real connection between skin color and DC value needs to be defined by the user.

When use AECG to do SpO2 testing, why on the DUT only can see R or IR light?


Please refer the answer to the question 1. First, roughly determine the positions of both PD/LEDs. DUT must be able to see the simulator output waveform and the both parties need to see each other. AECG reflective series, the R and IR positions are as shown in the photo below:

(For reference only)


B.How to determine that AECG has detected the optical signal of the DUT?

1): In the following screen of the AECG software, click on the “Sampling” (vertical writing) in the screen lowest left corner (do not start the simulator “Play” function at this time)

2): Click “Signal”, check Switch-RED & Switch – Infrared, as below photo:

3): Click “Sampling” (horizontal writing), start the sample function

4): Select the -/+ amplify range to properly display the detective intensity, as below photo:


5): May click “Freeze” function to freeze the captured waveform, as below photo:


6): Using TI AFE4403 EVM as DUT, can see the waveforms as follow figure:

Two lights should be interlaced startup (Low Active), if there is only high or only low Condition, the “Trigger Level” should be adjusted.


7): Trigger Level adjust explanation:


Dynamically adjust R/IR Trigger Level value without Freeze and proper magnification, the order is, first fix the IR at the maximum value of 255, because the IR switch will affect R switch. In this case, the switching mode of the IR should be at a high level, if it is at a low level, indicates that the simulator has a problem or the light of the DUT is too strong (need to adjust the hardware parameters of the simulator), if the IR is stable at the high level, you can further adjust the value of R, slowly adjust from high to low until you see the appropriate stable low level pulse, and then adjust the IR Trigger Level slowly decreases until you see a stable, interlaced low pulse.  At this point, it means that AECG can see the sequence of the DUT light turn on stably, if cannot get the correct adjustment, the AECG need to troubleshoot or adjust the inside hardware parameters of AECG.


C. Confirm DUT received the light of AECG

This part needs to be judged from the information received by the DUT. We recommend setting the two lights to different types of waves first. After adjusting the Trigger Level, stop Sampling and return to the following screen.

Select R or IR, as follows:

Select waveform type, as follows:


And then click ”Play” to play the waveform, as follows:


DUT is TI AFE 4403 EVM, the detected waveforms as follows:


There are 4 different waveforms, from top (C1) to bottom (c4):

C1: LED 1, IR LED turn on waveform (the sample data from IR LED turn on).

C2: LED 1 Ambient, IR LED turn off waveform, in general case, this is noise only low amplitude waveform, if it is not noise waveform, means the Trigger Level is not correct or DUT sampling way is unacceptable.

C3: LED 2/LED 3, R LED turn on waveform (the sample data from R LED turn on).

C4: LED 2/LED 3 Ambient, R LED turn off waveform.

SpO2 function quick introduction


The recursive formula as follows, the user must define the 110.0 and 25.0 parameters to get the DUT SpO2. Normally, to get the recursive line after clinical, and then determine these two values



Then, I want to change the SpO2 value, user can modify the PI(R) or PI(IR) value.

When modifying the SpO2 value, the checked (blue dot) PI(R) or PI(IR) will be modified automatically, as follows, when the SpO2 value change to 95%, the PI(R) change to 2.399.



As above, the “Lock DC” is unchecked, so the DC value will be modified when PI(R) modified, but the AC value will still the same.

User can modify all the values which can be changed, and the PI(R), PI(IR), SpO2 value will be changed automatically.



The value that can be entered in the above figure is the compensation for the customer to make the offset according to the condition of the system test fixture (this value may come from the circuit dark current / AFE offset error / external ambient light increase the DC level...).

Why does DUT receive waveforms from AECG100 with noise?

Possibility: Line/main frequency interference (e.g. 60Hz in Taiwan)

We could use AECG 100 and TI AFE4403 EVM to do some tests.

Test 1: 60Hz Notch Filter ON/OFF (AECG100 DC 625mV and AC 30mV)

Blue Line: Disable AFE4403 60Hz Notch Filter

Red Line: Enable AFE4403 60Hz Notch Filter



Test 2: Mobile Power Pack / USB Isolator

Blue Line: AECG100 PC software Mode, DC 3000mV, AC 30mV

Red Line: AECG100 standalone mode waveform output with power supply of mobile battery pack

Green Line: TI AFE4403 connects to USB Isolator



  1. It indicates that the interference mainly comes from the receiving end (TI AFE4403).
  2. It’s confirmed that USB Isolator could decrease the interference.
What is the response time of AECG100?

Please refer to above figure. The definition of response time is that the delay time between A (PD reception) and B (LED emitting). However, the optical signals between A and B are difficult to measure. Therefore, WhaleTeq uses oscilloscope to measure the electrical signals between A” and B” as the response time.

We’d expect your attention that the response time would be varied due to incident light intensity, emitted light intensity and trigger level. Please refer to the below figure.


A. Incident light intensity would influence the delay time. Thus T2 > T1. Moreover, please notice that the 

    incident light intensity would be affected by emitting intensity of DUT LED, relevant position (the distance

    and the angle between DUT PPG sensor and AECG100 diffusion film) and wavelength


B. Different trigger level leads to different response time. Please refer to the figure and you can tell T1/T2

    would be increased if the trigger level is increased.


C. There are 2 trigger levels for AECG100 and the relationship of these 2 trigger levels is –

    Trigger Level (OFF)=Trigger Level (ON) + OFFSET

    The OFFSET is generated by electrical circuit.

    *Trigger Level/OFFSET…are relative values and we haven’t calibrated those values as absolute values.


D. It’s possible that some DUT would have a longer LED off time and this is because of the large capacitance

    design of DUT


E. In accordance with our experience, most T1/T2 values are smaller than 1us while T3/T4 values vary from

    each DUT. Please notice that it’s possible to get an inappropriate test result when DUT is sampling after

    LED turns off per previously described as A’ in Q&A 4. Also, user could get another inappropriate test result

    when T3/T4 values are larger per described in D (large capacitance design of DUT).




As there’re too many variables, WhaleTeq’s test environment shall be different from customer’s test environment.


Therefore, the response time we advised is only for reference. We strongly suggest customer to test DUT with AECG100 to confirm the actual response time.

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