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PCF2119 Datasheet PDF : 83 Pages
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NXP Semiconductors
PCF2119x
LCD controllers/drivers
Table 6. Bias levels as a function of multiplex rate
Multiplex Number of Bias voltages
rate
bias levels V1
V2
V3
V4
V5
V6
1:18
5
VLCD
3--
4
(
VLC
D
–
VSS)
1--
2
(
VLCD
–
VSS)
1--
2
(
VL
CD
–
VSS)
1--
4
(
VL
C
D
–
VSS)
VSS
1:9
5
VLCD
3--
4
(
VLC
D
–
VSS)
1--
2
(
VLCD
–
VSS)
1--
2
(
VL
CD
–
VSS)
1--
4
(
VL
C
D
–
VSS)
VSS
1:2
4
VLCD
2--
3
(
VLC
D
–
VSS)
2--
3
(
VLCD
–
VSS)
1--
3
(
VL
CD
–
VSS)
1--
3
(
VL
C
D
–
VSS)
VSS
The RMS on-state voltage (Von(RMS)) for the LCD is calculated with Equation 3 and the
RMS off-state voltage (Voff(RMS)) with Equation 4:
Von(RMS)
=
VLCD
--a---2----+-----2---a----+-----n---
n × (1 + a)2
(3)
Voff(RMS)
=
VLCD
--a---2----–----2----a----+-----n---
n × (1 + a)2
(4)
where the values of a are
a = 2 for 1⁄4 bias
a = 3 for 1⁄5 bias
and the values for n are
n = 2 for 1:2 multiplex rate
n = 9 for 1:9 multiples rate
n = 18 for 1:18 multiplex rate.
Discrimination (D) is the ratio of Von(RMS) to Voff(RMS) and is determined from Equation 5
D = -V----o---n--(--R---M----S---) = (---a-----+-----1----)--2----+-----(--n-----–----1----)
(5)
Voff(RMS)
(a – 1)2 + (n – 1)
8.5.1 Electro-optical performance
Suitable values for Von(RMS) and Voff(RMS) are dependant on the LCD liquid used. The
RMS voltage, at which a pixel will be switched on or off, determine the transmissibility of
the pixel.
For any given liquid, there are two threshold values defined. One point is at 10 % relative
transmission (at Vlow) and the other at 90 % relative transmission (at Vhigh), see Figure 3.
For a good contrast performance, the following rules should be followed:
Von(RMS) ≥ Vhigh
(6)
Voff(RMS) ≤ Vlow
(7)
PCF2119X
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 9 — 14 April 2011
© NXP B.V. 2011. All rights reserved.
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