Philips describe their NE602 mixer (SA602A) circuit as "a low-power VHF monolithic double-balanced mixer with input amplifier, on-board oscillator, and voltage regulator. It is intended for high performance, low power communication systems. The guaranteed parameters of the SA602A make this device particularly well suited for cellular radio applications. The mixer is a "Gilbert cell" multiplier configuration which typically provides 18dB of gain at 45MHz. The oscillator will operate to 200MHz. It can be configured as a crystal oscillator, a tuned tank oscillator, or a buffer for an external LO. For higher frequencies the LO input may be externally driven. The noise figure at 45MHz is typically less than 5dB. The gain, intercept performance, low-power and noise characteristics make the SA602A a superior choice for high-performance battery operated equipment. It is available in an 8-lead dual in-line plastic package and an 8-lead SO (surface-mount miniature package)".
The later NE612 or SA612 is an improved pin for pin improved equivalent so if you can't find a 602 then look for a 612.
I am particularly indebted to Philips Components and Semiconductors Australia for their most generous assistance in giving me access to material presented on this page.
Low current consumption: 2.4mA typical
Excellent noise figure: <4.7dB typical at 45MHz
High operating frequency
Excellent gain, intercept and sensitivity
Low external parts count; suitable for crystal/ceramic filters
SA602A meets cellular radio specifications
Cellular radio mixer/oscillator
RF data links
HF/VHF frequency conversion
Instrumentation frequency conversion
Here are the pin configurations of the 602 mixer in figure 1 below.
Figure 1 - 602 mixer pin configurations
IN a (Pin 1)
One half of the balanced input.
IN b (Pin 2)
The other half of the balanced input.
Ground (Pin 3)
Output high is about 1.7V less than supply. Output high is capable of Isource up to 200mA while output low is capable of Isink up to 200mA.
OUTPUT a (Pin 4)
One half of the balanced output.
OUTPUT b (Pin 5)
Other half of the balanced output.
Oscillator base (Pin 6)
This is the input to the base of the oscillator transistor. See data sheet for comprehensive explanation.
Oscillator emitter (Pin 7)
This is the input to the emitter of the oscillator transistor. See data sheet for comprehensive explanation.
V+ (Pin 8)
This connects to Vcc. Note comments about effective supply filtering and bypassing this pin below under "General considerations with using a 602 mixer".
Figure 2 - block diagram of the 602 mixer
Vcc should lie between 4.5V DC min. and 8V DC max regulated.
Input signal frequency is typically up to about 500 Mhz, while typically the oscillator will work beyond 200 Mhz.
At 45 Mhz signal input the noise figure is quoted as 5.5 dB max although typically less than that.
The output impedance of the mixer (pins 4 and 5) is 1K5 (1,500 ohms) and the mixer needs to see that impedance.
The SA602A is designed for optimum low power performance.When used with the SA604 as a 45MHz cellular radio second IF and demodulator, the SA602A is capable of receiving -119dBm signals. The RF inputs (Pins 1 and 2) are biased internally. They are symmetrical. The equivalent AC input impedance is approximately 1.5k || 3pF through 50MHz. Pins 1 and 2 can be used interchangeably, but they should not be DC biased externally.
Over time I've come across a lot of nifty circuits using the SA/NE602 or SA/NE612. I'll present here a number of schematics.
Firstly there is a strong body of opinion which states the input and output impedances of the SA/NE602 are 1K5 ONLY for single ended configurations whereas, for either balanced input or output the impedance is 3K. Here in fig 3 below are a number of possible configurations for the SA/NE602. This is NOT an exhaustive list of all possible configurations. Obviously I've left out the oscillator etc. which we will deal with later.
Figure 3 - possible configurations for the SA/NE602 mixer
How about we deal with the impedance levels marked "A"?
From transformer theory we know this is going to be the square of the turns ratio we decide to use. Assume on the input side we are connecting to 50 ohms (could be anything) then if we are matching to 3K balanced, the turns ratio is the square root of 3,000 / 50 or about 7.75 : 1
If it was 1K5 then it's the square root of 1,500 / 50 or about 5.48 : 1
Same principle applies to the output side. Of interest to people constructing DC Receivers is the schematic in fig 3-d. Here is a balanced output of audio frequency which we would feed to a suitable audio amplifier such as the LM380 series of devices.
Some sample oscillator circuits using the SA/NE602 mixer are below:
Figure 4 - possible oscillator configurations using the SA/NE602 mixer
You really should download the 602 mixer data sheet - (109K) which is in PDF format. This way you get all the needed information.
A few folks have written to me about the difficulty of obtaining the NE602. My friend Dieter (DIZ) Gentzow - W8DIZ - Loveland, Ohio U.S.A. usually has them in stock. Pay by PayPal or check!
Here are some NE602/612/615 oscillator circuits I've encountered from a variety of sources. This includes both fixed and variable oscillators as well as fixed and variable crystal oscillators - all in the HF region.
Note that up in the VHF region it is almost impractical to design variable oscillators, the drift will kill you. I'd recommend using 3rd or 5th overtone oscillators using crystals, see "Figure 9. Typical Application for Cellular Radio" from the 602 mixer PDF data sheet.
602 mixer data sheet - (109K) in PDF format.
NE602/612/615 oscillator circuits
NE/SA615 Double Balanced Mixer and FM IF System
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Bibliography: - Philips Semiconductors - Semiconductors for Wireless Communications 1999 - IC17
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