TK14588V 데이터 시트보기 (PDF) - Toko America Inc

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TK14588V

FM IF IC

Toko America Inc  

TK14588

CIRCUIT DESCRIPTION (CONT.)

The RSSI output is a current output. It converts to a voltage by an external resistor between Pin 15 and GND. The time

constant of the RSSI output is determined by the product of the external converting resistance and parallel capacitance.

When the time constant is longer, the RSSI output is less likely to be influenced by a disturbance or the component of

amplitude modulation, but the RSSI output response is slower. Determine the external resistance and capacitance by the

application.

VCC

OUTPUT

CURRENT

RSSI- OUT

Current-to-Voltage

Transformation Resistor

FIGURE 2 - RSSI OUTPUT STAGE

The slope of the RSSI curve characteristic can be modified by changing the external resistance. In this case, the maximum

range of converted RSSI output voltage is GND level to about VCC - 0.2 V (the supply voltage minus the collector saturation

voltage of the output transistor).

In addition, the temperature characteristic of the RSSI output voltage can be modified by changing the temperature

characteristic of the external resistor. Normally, the temperature characteristic of the RSSI output voltage is very stable

when using a carbon resistor or metal film resistor with a temperature characteristic is 0 to 200 ppm/ °C.

This product is very accurate, because the RSSI characteristic is trimmed individually.

AM Demodulation by Using the RSSI Output:

Although the distortion of the RSSI output is high because it is a logarithmic detection of the envelope to the IF input, AM

can be demodulated simply by using the RSSI output. In this case, the input dynamic range that can demodulate AM is

the inside of the linear portion of the RSSI curve characteristic (see Figure 3B).

This method does not have a feedback loop to control the gain because an AGC amplifier is not necessary (unlike the

popularly used AM demodulation method). Therefore, it is a very useful application for some uses because it does not

have the response time problem.

Figure 3A shows the AM demodulated waveform.

Operating Condition

V = 3 V, f = 10.7 MHz,

CC

IN

fm = 40 kHz, Mod = 80%,

VIN = 40 dBm

RSSI-OUT (V)

AM can be

demodulated

inside of linear

range

100mV/div

100µs/div

FIGURE 3A - AM DEMODULATED WAVEFORM

Page 14

RF INPUT - LEVEL (dBu)

FIGURE 3B

January 2000 TOKO, Inc.

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