CXA3271GE 데이터 시트보기 (PDF) - Sony Semiconductor

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CXA3271GE

Fingerprint Sensor

Sony Semiconductor 

CXA3271GE

Cs

Vcel

Cp

Sensor block

(192 × 128)

S4

Cf1

Sr

Vsl

S5

S3

Vdmy

Vsns

S_Amp

Cp'

S11 S2 S1

VM VH

VL

Sense amplifier block

(192)

S6

Cf2

Voi

Voo

Sc

S7

Ch1

O_Amp

VOS

Buf

Ch2

Output block

(1)

Aout

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

VH – VM ≈ VM – VL

• Detailed description of operation

(All switches are off in the default status.)

1. S1, S4, Sr and S11 are turned on, Vcel is set to voltage VH, and Vdmy is set to voltage VL.

Vcel accumulated charge (Cs + Cp) VH

Vdmy accumulated charge Cp' VL

2. S1, Sr and S11 are turned off.

3. S2 is turned on and Vsl is set to VM.

4. S4 is turned off.

5. Sr, S3 and S5 are turned on.

At this time, the charge level that moves from Vcel and Vdmy to Vsl (actually between capacitances) is:

(Cs + Cp) (VH – VM) – Cp' (VM – VL) ≈ Cs (VH – VM)

This means that the sense amplifier gain is determined independently of the parasitic capacitance,

making it possible to obtain the required large signal dynamic range.

Vsns = VM – Cs (VH – VM)/Cf1

The voltage Vsns determined as shown above is accumulated in Ch1.

6. S5 is turned off.

7. S6 is turned on and the Voi voltage is set to VOS.

8. S6 is turned off.

9. Sc and S7 are turned on.

At this time, the charge level that moves from Ch1 to Cf2 is:

(VOS – Vsns) Ch1

This determines the Voo voltage which is accumulated in Ch2 and output to Aout via the buffer.

– 10 –

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