– 9 –

CXA3621GE

Fig. 2

• Fingerprint sensor operation (Fig. 2)

Description of characters

Cs:

Capacitance formed between the finger and the metal electrode

Cp: Parasitic capacitance formed between the metal electrode and the silicon substrate

Cp': Capacitance for canceling Cp (Cp

≈ Cp')

Ch

∗: Hold capacitance

Cf

∗: Feedback capacitance for determining the gain

S

∗: Switch

V

∗: Node voltage

VM =

1

2

4

11

Sr

S4

S3

SVss

Cf1

Cf2

Cs1

SS

Ssig

VM

Sense amplifier block

(192: Sensor cell)

(1: Dummy block)

Sensor block

(192

× 128: Sensor cell)

(128: Dummy block)

Upper: Sensor cell

Lower: Dummy block

Output block

(1)

S5

Sc

Cs

Cp

Cp'

Vcel

Sensor Array

Dummy Block

Vsl

S_Amp

P_Amp

VM

Cf2

SD

Sdmy

P_Amp

VM

Ch1

Cf3

S6

S7

O_Amp

VOS

Ch2

Voi

Voo

Buffer Aout

Vsns

Sr

S4

S3

SVss

Cf1

VM

S5

Sd1

Cp

Cp'

Vceld

Vsld

S_Amp

Ch1

Vsnsd