NJW1124 View Datasheet(PDF) - Japan Radio Corporation

Part Name

Description

MFG CO.

NJW1124

Voice Switched Speakerphone circuit

Japan Radio Corporation  

NJW1124

Notes:2:

Filter circuit using Receive amplifier, Mic. Amplifier, Line amplifier.

Receive amplifier, Mic. Amplifier, Line amplifier enable to form active filter circuit which is 1st order or 2nd order,

HPF or LPF or BPF.

1.1st order HPF,LPF circuit example

Fig.13 shows 1st order (-6dB/oct) HPF, LPF circuit.

Combining HPF formed by Co and R1, and LPF formed by C1 and R2, forms BPF.

(Co should be also used typical application as DC decoupling.)

C0

Receive In

R1

FI

C1

R2

FO

Ref

Fig.13 1st order HPF,LPF circuit example

fC ( HPF )

=

1

2πC0 R1

fC (LPF )

=

1

2πC1R2

Response

+6dB/oc

-6dB/oct

fc(HPF)

fc(LPF)

Frequency

2.2nd order LPF circuit example

Fig.14 shows 1st order (-12dB/oct) LPF circuit.

Same as 1st order filter, Co should be used as DC decoupling. C2 selecting arbitrarily, Butterworth filter forming

coefficient is as below.

R2

C2

C0

R1

R3

Receive In

FI

C1

FO

Ref

Fig.14 2nd order LPF circuit example

Response

+6dB/oc

-12dB/oct

R1 = 2

1

2GπfC(LPF )C2

R2 = 2

1

2πfC(LPF )C2

R3 = 2

1

2(G + 1)πfC(LPF )C2

C3 = 2(G + 1)C2

G = Gain

fc(HPF)

fc(LPF)

Frequency

fC(HPF) is same as 1st order type above.

– 27 –

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