Philips Semiconductors
Universal LCD driver
for low multiplex rates
Preliminary specification
PCF8562
Discrimination is the ratio of Von to Voff, and is determined by the formula V-V----oo---fn-f = (-(--aa-----+–----1-1---))--2-2---+-+----((---NN------––----11----))-
Using the above formula, the discrimination for an LCD drive mode of 1 : 3 with 1⁄2bias is 3 = 1.732, and the
discrimination for an LCD drive mode of 1 : 4 with 1⁄2bias is ----3-2---1-- = 1.528.
The advantage of these LCD drive modes is a reduction of the LCD full-scale voltage VLCD as follows:
• 1 : 3 multiplex (1⁄2 bias): VLCD = 6 × Voff(rms) = 2.449 Voff(rms)
• 1 : 4 multiplex (1⁄2 bias): VLCD = (---4-----×--3-------3----) = 2.309 Voff(rms)
These compare with VLCD = 3 Voff(rms) when 1⁄3 bias is used.
Table 2 Discrimination ratios
LCD DRIVE MODE
static
1 : 2 multiplex
1 : 2 multiplex
1 : 3 multiplex
1 : 4 multiplex
NUMBER OF
LCD BIAS
BACKPLANES LEVELS CONFIGURATION
1
2
static
2
3
1⁄2
2
4
1⁄3
3
4
1⁄3
4
4
1⁄3
V-----oV--f--f-l(-c-r--md----s--)
0
0.354
0.333
0.333
0.333
V-----oV--n--l-(-c-r-m-d---s---)
1
0.791
0.745
0.638
0.577
D = V-V----oo--f-n-f-((--rr--mm----ss--))
∞
2.236
2.236
1.915
1.732
November 22, 2004
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