AMOLED vs PMOLED | Driving Method, Size Limits & Cost

AMOLED and PMOLED differ in one engineering decision — how each pixel receives its current — and nearly everything else follows from it. Active matrix gives every pixel a transistor and a storage capacitor; passive matrix scans rows and columns and relies on a duty cycle. That choice sets the practical size ceiling, the shape of the cost curve and the ageing behaviour, so it is worth understanding before comparing quotes.

The driving method is the root difference

In a passive matrix, anodes run as rows and cathodes as columns. The driver energises one row at a time and applies data to the columns; the pixel at each intersection emits only while its row is selected. With N rows, each pixel is on for roughly one Nth of the frame.

To deliver a given average luminance, the instantaneous current must therefore be roughly N times higher than the average. That multiplication is the central fact of passive matrix design: it drives the peak current requirement, the voltage drop along the row and column lines, and the rate at which the organic material ages.

In an active matrix, each pixel holds its own charge in a capacitor for the whole frame. The pixel emits continuously, the peak-to-average ratio approaches one, and the row count stops dictating how hard each pixel must be driven. The cost moves from the drive scheme into the backplane: a thin-film transistor array must be built under the organic stack, with enough uniformity that neighbouring pixels match.

Why the duty cycle caps the size

Increasing rows in a passive matrix lowers the duty cycle, which raises the required peak current, which increases both the IR drop along the transparent electrodes and the stress on the organic layer. Beyond a certain row count the panel either cannot reach the required brightness or reaches it at a lifetime the product cannot accept. This is why passive matrix panels cluster in the small formats — character displays and modest graphic panels — rather than competing across the size range.

Active matrix has no such ceiling in principle; it is limited instead by backplane yield and cost, which is why AMOLED panels scale from watch-sized displays up to large televisions.

What the cost difference actually is

Passive matrix saves the backplane. It needs fewer photolithography steps, no TFT array, and a simpler driver IC with a straightforward scan scheme. For a small character or icon display, that structure is genuinely cheaper to build.

Active matrix pays for the TFT array and for the compensation circuitry that corrects its non-uniformity, but it can use a simpler scan because the pixels hold their state. The comparison that matters commercially is not cost per square millimetre but cost at the size and resolution the product requires: below a certain resolution and panel area, passive matrix is cheaper; above it, the duty-cycle penalty makes high-brightness operation impractical and the comparison stops being like for like.

Uniformity, contrast and ageing

Both families are emissive and both produce true black by switching the pixel off, so on-axis contrast is high for both. The differences appear across the panel and over time.

Uniformity. A passive matrix panel's brightness depends on the duty cycle and the electrode resistance; larger panels show more variation along the rows. An active matrix panel's uniformity depends on transistor matching, which is why AMOLED drivers include compensation.

Ageing. Passive matrix pixels age under high instantaneous current, so lifetime is strongly tied to the brightness the user selects. Active matrix pixels age more slowly per unit of brightness but differ between colours and pixels, which is what produces residual images when a static element stays on screen.

Where each one wins

Requirement	Favours PMOLED	Favours AMOLED
Small character or icon display	Yes — simplest cost structure	Over-specified
High resolution in a small area	Duty-cycle penalty	Yes
High brightness, continuous	Shortens lifetime quickly	Yes
Lowest possible unit cost	Yes	Backplane dominates
Graphical content, gradients	Limited by uniformity	Yes
Simple driver and interface	Yes	Needs compensation logic

The row worth studying is brightness. A product that runs its display at high brightness all day gains little from passive matrix's lower cost, because the lifetime cost arrives later as field returns. A product that shows short readings at moderate brightness most of the time sits exactly where passive matrix makes sense.

Specifying either family correctly

Three figures decide whether a quote is meaningful, and they are often quoted without their conditions:

• Luminance at the operating point, not only at maximum, with the duty cycle or drive setting stated.
• Lifetime defined as hours to a stated fraction of initial luminance at a stated brightness — a half-life at one brightness does not transfer to another.
• Uniformity figure, typically as a percentage across a stated number of measurement points.

The measurement basis for luminance, contrast and uniformity is standardised in ISO 9241-307^[1], and the wider trade between emissive and backlit technologies is surveyed in the display literature^[2].

Active matrix modules are listed in the AMOLED display collection and passive matrix modules in the PMOLED display collection; small character OLEDs in both families are grouped under character OLED displays.

AMOLED and PMOLED differ in driving method, and that difference sets the size ceiling and the cost curve. Passive matrix wins on simplicity and unit cost at small sizes with simple content; active matrix wins wherever resolution, brightness or graphical content push against the duty-cycle penalty. Specify luminance and lifetime with their conditions, and the comparison becomes decidable.

References

1. ISO 9241-307:2008 — Ergonomics of human-system interaction — Part 307: Analysis and compliance test methods for electronic visual displays. International Organization for Standardization. https://www.iso.org/standard/40102.html
2. Hilsum, C. (2010). Flat-panel electronic displays: a triumph of physics, chemistry and engineering. Philosophical Transactions of the Royal Society A, 368(1914), 1027–1082. https://doi.org/10.1098/rsta.2009.0247