Direct Conversion Radio Receiver Using the NE602 IC Double Balanced Mixer Product Detector

NE602/SA602A is a high-performance and low power double-balanced active radio frequency mixer/product detector with an on-chip oscillator, input amplifier and voltage regulator. This mixer/product detector IC contains the Gilbert cell differential amplifier or multiplier, which provides optimal mixer characteristics such as good port-to-port isolation, high gain, higher operating frequency, low noise etc.

 

This mixer provides about 18 dB of gain at 45 MHz. The in-built oscillator operates upto about 200 MHz. The oscillator section can be configured as a variable frequency oscillator, crystal oscillator or as a buffer amplifier for an external local oscillator.

 

The NE602 mixer/product detector IC is superior in terms of gain, intercept performance, low noise and low power characteristics. This IC is available as an 8-pin DIL or SO package.

The Important Features of the NE602 IC are,

1. Low current consumption of typically 2.4 mA.
2. Excellent noise figure of less than 5 dB at 45 MHz.
3. High operating frequency.
4. Excellent gain, intercept and sensitivity.
5. Low external parts count, therefore easier to build.

NE602 IC Product Detector Considerations
In this direct conversion receiver, the NE602 IC acts as a product detector. This IC is able to provide high dynamic range, if the input signal levels are not exceeded as specified by the manufacturer. It has the ability to accomodate large signals without degraded intermodulation distortion. A bandpass filter and RF amplifier stage at the input provides enough gain with good signal to noise ratio. The RF input pins and the output pins are biased internally and therefore do not need to bias externally.

 

 

Local oscillator injection level is about 200 mV, which also gives adequate dynamic range and mixer gain. Mixer noise figure comes to around 5 dB at 45 MHz. The output is obtained as an audio signal, which is filtered using a low pass audio filter and amplified by an audio power amplifier.

Circuit Description
The NE602 product detector circuit is wired onto a PCB. An LC tank circuit is attached between the 1st and 2nd pins of the IC. The tank circuit is tuned to the required frequency of operation. The 2nd pin is grounded using a 0.01uF capacitor. The RF input is given through a small value coupling capacitor to the LC tank circuit or through a primary winding on top of the tank circuit.

 

 

The pins 6 and 7 are used for the purpose of an in-built LC oscillator or crystal-controlled oscillator. This in-built oscillator operates upto around 200 MHz. An external local oscillator or VFO signal of about 200mV peak to peak can also be given to the 6th pin of the IC to drive this mixer. The audio output is obtained through the 5th pin through a coupling capacitor. A regulated supply voltage of 6-8 volts is given through the 8th pin of the IC.

Applications of NE602 IC
The NE602 IC is used in applications such as,

1. Cellular radio mixer/oscillator.
2. Portable radio systems.
3. VHF transceivers.
4. RF data links.
5. HF/VHF frequency conversion.
6. Instrumentation frequency conversion.