What Are Supported by CamJ?

CamJ provides a high-level interface that describes some commonly-used analog and digital structures. Users can directly plug-in CamJ APIs in their image sensor designs. Here we summarize these hareware structures.

Analog Domain

The figure shown below presents all the analog components that are supported by CamJ.

In this figure, the top level shows the algorithmic operations that are currently supported in CamJ. The second level shows the analog components that support the algorithmic operations at the top level. The bottom level shows the major basic analog components that compose the analog components at the second level. Both the energy and noise modeling in CamJ are performed in the analog components at the bottom level. The energy and noise modeling at the second level are composed by the bottom level analog component.

CamJ Analog Interface

To make CamJ easy to use, we expose the second-level as our standard interface. Expert users can also extend our standard interface to implement more complex analog compoenent in their design. In later Sections, we also introduce how to extend our standard interface.

The table below shows the overview of analog components at the second level:

Component Name	Functionality		Building Blocks	Schematic
	Algorithmic Ops	Mathematic Expression
3T Active Pixel Sensor (3T-APS)	Sensing	-	Photodiode (PD), Floating Diffusion (FD), Source Follower (SF)
4T Active Pixel Sensor (4T-APS)	Sensing	-	Photodiode (PD), Floating Diffusion (FD), Source Follower (SF)
Digital Pixel Sensor (DPS)	Sensing	-	Photodiode (PD), Floating Diffusion (FD), Source Follower (SF), ADC
Pulse Width Modulation Pixel (PWM Pixel)	Sensing	-	Photodiode (PD), Ramp, Comparator (CMP)
Analog-to-Digital Convertor (ADC)	Conversion, Quanization	-	ADC
Digital-to-Current Convertor (DAC)	Conversion	-	DAC
Comparator	Compare	(In1 > In2) ? In1 : 0	Comparator (CMP)
AnalogReLU	ReLU	(In > 0) ? In : 0	Comparator (CMP)
Passive Average	Average		Passive Switched Capacitor Array (PSCA), Source Follower (SF)
Active Average	Average		Amplifier (AMP)	-
Passive Binning	Binning		Passive Switched Capacitor Array (PSCA), Source Follower (SF)
Active Binning	Binning		Amplifier (AMP)	-
Voltage-to-Voltage Convolution	Convolution		Passive Switched Capacitor Array (PSCA), Source Follower (SF)
Time-to-Voltage Convolution	Convolution		Current Mirror (CM), Passive Analog Memory (PAM)
Binary Weight Convolution	Convolution		Amplifier (AMP)
Passive Analog Memory	Store	-	Passive Analog Memory (PAM)
Acitve Analog Memory	Store	-	Active Analog Memory (AAM)
Max Pool	Max Pooling		Amplifier (AMP)
Max Voltage	Max		Amplifier (AMP)
Adder	Add		Amplifier (AMP)
Subtractor	Subtraction		Amplifier (AMP)
Absolute Difference	Absolute Difference		Amplifier (AMP) Comparator (CMP)

Analog Design Check Rules

In ensure the correctness of user’s implementation, CamJ provides a set of rules to check the correctness of user’s sensor designs in analog domain:

Input/Output Size Compatibility This rule enforces that an analog component has a sufficient number of producers to generate inputs if an analog component requires multiple input sources.

Domain Compatibility This rule enforces that each connected analog component pair has compatible input and output interfaces. For instance, if the producer component’s output signal is in voltage domain, then, the input signal of the corresponding consumer component should be also in voltage domain.

Input Driver Compatibility This rule ensures that the producer needs to have a driver if the corresponding consumer component requires a driver to drive the input signal.

How to Extend CamJ Interface

In addition to using Cam standard interface, users can also implement their own customized analog component class. For each customized component class, users need to implement two main functions:

• energy(self): which calculates the energy consumption of this analog component when generating a given number of outputs. This given number of outputs should match num_output when assigning this customized analog component to an AnalogComponent instance.

• noise(self, input_signal_list: list): which defines how signals are processed in this analog component. The return of this function should be a tuple. The first element in this tuple is the name of this analog component in str, the second element is the processed signals.

Digital Domain

The interface in digital domain is much concise. Unlike analog domain, which has a handful of simulators or synthesis tools, designers can easily obtain per-cycle/access memory of their digital structures via simulators or synthesis tools. Therefore, instead of providing low-level structure blocks, we provide rather high-level interface for users. This is because of the design philosophy of CamJ: it is not used to generate digital accelerators; rather, it helps assess how an accelerator fits in the entire computational CIS system. For that reason, CamJ expects designers to have a preliminary design of the digital accelerators (whether it’s your manual design, HLS generated, or a licensed IP), in which case one will have the per-cycle/access energy statistics.

The figure shown below presents the digital interface supported by CamJ. For more details, please check out camj.digital package.