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What is the PWM+PAM Hybrid Driving Technology?
PWM+PAM hybrid driving technology is a driving method for LEDs that simultaneously leverages the time dimension of PWM (i.e., “how long” the LED stays on) and the current-amplitude dimension of PAM (i.e., “how bright” the LED gets). Through two-dimensional joint modulation of time and current, it achieves comprehensive optimization among grayscale, refresh rate, and power consumption.
1. How Pure PWM Represents Grayscale Using Pulse Duration
The grayscale value g is expressed by the duty cycle D(g):
From this, we can see that grayscale equals the fixed current multiplied by the varying ON-time duration.
Its advantages are:
a. Simple driving scheme, good linearity (theoretically), and flexible performance at mid-to-high grayscales.
Its bottlenecks are:
a. Low grayscales require extremely short pulse widths, which are constrained by GCLK, LED switching speed, and EMI limitations. This results in inaccurate low-gray brightness, failure to illuminate, or very low visual refresh rates.
b. Extending the dynamic range by further lengthening the PWM period leads to slower panel refresh or forces GCLK to increase even further.
2. How Pure PAM Represents Grayscale Using Current Amplitude
The grayscale value g is represented by the current I(g):
From this, we obtain that grayscale equals varying current multiplied by a fixed ON-time duration.
Its advantages are:
a. Low grayscales can be resolved directly via current amplitude within a fixed refresh period, which greatly improves low-gray refresh performance and avoids ultra-short pulse widths;
b. Well suited for scenarios such as “static driving.”
Its bottlenecks are:
a. The LED current–luminous-flux curve exhibits significant non-linearity. The low-current region is susceptible to threshold effects, current-mirror mismatch, and temperature drift, resulting in large color shifts and brightness errors;
b. Implementing a high-precision digital-to-analog conversion (DAC) circuit with a wide dynamic range inside the driver IC entails high cost and design complexity.
3. PWM+PAM Hybrid Driving Technology
The primary goal is to “stack” the advantages of both PWM and PAM, leveraging the strengths of each. From a design perspective, LED display performance is enhanced in the following aspects:
Reduced flicker at low grayscales: In the low-grayscale region, the approach of “reducing current + increasing pulse count” replaces a “single ultra-short pulse width.” This raises the equivalent repetition frequency 
of single-pixel luminance modulation, thereby suppressing flicker.
Preserved dynamic range at mid-to-high grayscales: In the high-grayscale region, PWM (time-domain control) is still predominantly relied upon to extend bit depth and peak brightness, avoiding the “reduced efficiency / overheating” that would result from using PAM alone at high currents.
Global grayscale linearity + controllable color accuracy: By partitioning the grayscale range (into low, mid, and high segments) and assigning different PWM/PAM combinations to each, together with correction LUTs, the physical non-linearity of the LED and the non-linearity of the drive chain are flattened as much as possible.
Controlled power consumption and temperature: In certain ranges, appropriately lowering the current combined with a reasonable duty cycle achieves a lower average current at the same brightness, reducing both power consumption and thermal load.
If we assume the luminance signal of a single pixel within a certain refresh period T is:
where:
• 
: the number of pulses corresponding to grayscale g (PWM dimension);
• 
: the current amplitude of the k-th pulse (PAM dimension);
• 
: a window function that equals 1 during the interval
and 0 at all other times.
Then traditional PWM driving yields:
Grayscale is achieved solely via 
.
Traditional PAM driving yields:
so brightness can only be adjusted via 
.
Hybrid PWM+PAM sets different combination rules for different grayscale ranges (low / mid / high):
• Low grayscale: Appropriately reduce 
and increase 
, while keeping each 
above its physical lower limit, to improve 
;
• Mid grayscale: Primarily PWM-based, with PAM used for fine-tuning or compensation;
• High grayscale: Limit excessive current rise; mainly rely on PWM time allocation to extend the dynamic range.
By selecting an appropriate average current through hybrid PWM+PAM modulation, the LED emitter chip operates within its highest-efficiency region. In the low grayscale range, PWM precisely controls emission duration to avoid brightness discreteness; in the high grayscale range, PAM increases current amplitude to reduce high-frequency PWM switching losses, balancing high grayscale brightness performance with low power requirements. Compared with pure PWM driving, this technology effectively addresses issues such as flicker and high-grayscale brightness loss. While improving display dynamic range, color accuracy, and visual refresh rate, it also reduces device temperature rise, providing key technical support for high-density, high-quality LED display applications.
Fig.1 Timing diagram of hybrid driving
Concept of different LED dimming schemes. 
is the maximum forward current of an LED. Under PWM, the average current is controlled by the duty cycle. Under AM the average current is a directly controlled variable. Hybrid PWM/AM uses variable peak current and variable duty cycle to control the average forward current. Different combinations of peak current and duty cycle can be used to obtain the same value of the average current.
As MLED (Mini/Micro LED) evolves toward higher pixel density, greater dynamic range, and more demanding application scenarios (e.g., virtual production/filming, MLED TVs, and automotive transparent displays), NovaStar’s stepless solution with PWM + PAM hybrid driving technology has gradually demonstrated its inevitability and core advantages.
