TK14551V Ver la hoja de datos (PDF) - Toko America Inc
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TK14551V Datasheet PDF : 32 Pages
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TK14551V
CIRCUIT DESCRIPTION
RSSI, RSSI Buffer Amplifier:
Because the RSSI output of this product is a dual output, it has various uses. Because it includes a dual high-speed RSSI
output, it is possible to sense the carrier level and to demodulate AM at the same time.
The RSSI output is a current output. It converts to a voltage by an external resistor between Pin 28,19 and GND. The
time constant of the RSSI output is determined by the product of the external converting resistor and parallel capacitor.
When the time constant is longer, the RSSI output is more immune to disturbances or the component of amplitude
modulation, but the RSSI output response is lower. Determine the external resistor and capacitor with this in mind.
It is possible to modify the slope of the RSSI curve characteristic by changing the external resistor. 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, it is possible to modify the temperature characteristic of the RSSI output voltage 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 of 0 to 200 ppm/ °C.
This product is very accurate, because the RSSI characteristic is trimmed individually.
Both systems of RSSI output are connected to individual buffer amplifiers with an internal gain of 1. Therefore, even if
the load impedance is heavy, it is possible to take out the RSSI output signal from the buffer amplifier output. The
maximum input and output level of this buffer amplifier is VCC - 1.0 V.
VCC
OUTPUT
CURRENT
18,
19
RSSI- OUT
Current-to-Voltage Transformation Resistor
FIGURE 3 - RSSI OUTPUT STAGE
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 4).
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 doesn’t
have the response time problem.
January 2000 TOKO, Inc.
Page 21
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