NJM2211M データシートの表示（PDF） - Japan Radio Corporation

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NJM2211M

FSK DEMODULATOR / TONE DECODER

Japan Radio Corporation  

NJM2211

Design Instructions

The circuit of Figure 4 can be optimized for any tone-detection application by the choice of five key circuit

components : R0, R1, C0, C1, and CD. For a given input tone frequency, fS, these parameters are calculated as follows :

1. Chose R0 to be in the range of 15kΩ to 100kΩ. This choice is arbitrary.

2. Calculate C0 to set center frequency, f0 equal to fS : C0=1 / R0fs.

3. Calculate R1 to set bandwidth ±∆f (see Design Equation No.5) : R1=R0 (f0 / ∆f)

Note : The total detection bandwidth covers the frequency range of f0=∆f

4. Calculate value of C1 for a given loop damping factor :

C1=C0 / 16ξ2

Normally ξ ≈ 1 / 2 is optimum for most tone-detector applications, giving C1=0.25 C0.

Increasing C1 improves the out-of band signal rejection, but increases the PLL capture time.

5. Calculate value of filter capacitor CD. To avoid chatter at the logic output, with RD=470kΩ, CD must be :

CD (µF) ≥ (16 / capture range in Hz)

Increasing CD slows the logic output response time.

Design Examples

Tone detector with a detection band of 1kHz±20Hz :

Step 1 : Choose R0=20kΩ (18kΩ in series with 5kΩ potentiometer).

Step 2 : Choose C0 for f0=1kHz : C0 =0.05µF.

Step 3 : Calculate R1 : R1=(R0)(1000 / 20)=1MΩ.

Step 4 : Calculate C1 : for ξ=1 / 2, C1=0.25µF, C2=0.013µF.

Step 5 : Calculate CD : CD=16 / 38=0.42µF.

Step 6 : Fine tune the center frequency with the 5kΩ potentiometer, RX.

Linear FM Detection

The NJM2211 can be used as a linear FM detector for a wide range of analog communications and telemetry

applications. The recommended circuit connection for the application is shown in Figure 5. The demodulated output is

taken from the loop phase detector output (pin 11), through a post detection filter made up of RF and CF, and an external

buffer amplifier. This buffer amplifier is necessary because of the high impedance output at pin 11. Normally, a

non-inverting unity gain op amp can be used as a buffer amplifier, as shown in Figure 5.

Figure 5. Linear FM Detector

The FM detector gain, i.e., the output voltage change per unit of FM deviation, can be given as :

VOUT=R1 VR/100 R0 Volts/% deviation

where VR is the internal reference voltage. For the choice of extrernal components R1, R0, CD, C1 and CF, see the

section on Design Equations.

Ver.2003-12-09

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