SL6654 IF/AF for FM 

FEATURES

• Low Power Consumption (1.5mA)
• Single Chip Solution
• Guaranteed 100MHz Operation
• Exceptionally Stable RSSI

APPLICATIONS

• Cellular Radio Telephones
• Cordless Telephones

QUICK REFERENCE DATA

• Supply Voltage 2.5V to 7.5V
• Sensitivity 3µV
• Co-Channel Rejection 7dB

The SL6654 is a complete single chip mixer/oscillator, IF amplifier and detector for FM cellular radio, cordless telephones and low power radio applications. It features an exceptionally stable RSSI (Received Signal Strength Indicator) output using a unique system of detection. Supply current is less than 2mA from a supply voltage in the range 2.5V to 7.5V
The SL6654 is a very low power, high performance integrated circuit intended for IF amplification and demodulation in FM radio receivers. It comprises:

• A mixer stage for use up to 100MHz
• An uncommitted transistor for use as an oscillator
• A current sink for biasing this transistor
• A limiting amplifier operating up to 1.5 MHz
• A quadrature detector with differential AF output
• An RSSI (Received Signal Strength Indicator) output

The mixer is single balanced with an active load. Gain is set externally by resistor although the value is usually determined by that required for matching into the ceramic filter. It is possible to use a tuned circuit, but an increase in mixer gain will result in a corresponding reduction of the mixer input intercept point. The RF input is a diode biased transistor with a bias current of typically 300µA. The oscillator input is differential but would be driven single-ended. Particular care should be taken to avoid accidental overload of the oscillator input. 

The oscillator consists of an uncommitted transistor and a separate current sink. The user should ensure that the design of oscillator is suitable for the type of crystal and frequency required; it may not always be adequate to duplicate the design shown in this data sheet.

The limiting amplifier is capable of operation to at least 1 MHz, and the input impedance is set by an external resistor to match the ceramic filter. Because of the high gain, pins 12 and 13 must be adequately bypassed.

A conventional quadrature detector is fed internally from the IF amplifier; the quadrature input is fed externally using an appropriate capacitor and phase shift network. A differential output is provided to feed a comparator for digital use, although it can also be used to provide AFC.

The RSSI output is a current source with the value proportional to the logarithm of the IF input signal amplitude. There is a small residual current due to noise within the amplifier (and mixer), but beyond this point, there is a measured and guaranteed 70dB dynamic range. The typical range extends to 92dB, independent of frequency, and with exceptionally good temperature and supply voltage stability.