EMRFD Message Archive 68

Message Date From Subject
68 2006-08-03 23:20:32 Frank Question on how to use NE602
I flipped through the pages of EMRFD - I'm sure it's in there, but I
did not find it. I've got the device data sheet in front of me, and
it's not in there, as far as I can see.

I am using four NE602 mixer/oscillators ICs in a circuit that requires
the same oscillator feeding all of them. Therefore, at least three of
them must be fed a mixing signal externally. While the data sheet
claims this can be done, there is no mention of how - what is the
right signal level to feed to the IC, and how do you get the internal
oscillator from oscillating?

Looking at the equivalent circuit, I surmise that if I simply tie pins
6 and 7 together, I will drive the BE junction of the oscillator to
zero volts, thus disabling the oscillator. Remaining will be a
resistor to Vcc and GND; thus I need to capacitivly couple to the
newly-created node to avoid upsetting the resulting DC bias condition.

As described, the junction of pins 6 and 7 becomes the input to the a
stage labelled "buffer". What is the appropriate drive level for this
"buffer" and what is the effective input impedance?


69 2006-08-04 04:12:56 Steven S. Coles Re: Question on how to use NE602

The last figure in Philips application note AN1983 shows leaving pin
7 (emitter) open and driving pin 6 (base). However, that's a bit
different from your application. I recommend downloading Philips
application notes AN1777, AN1981, AN1982, and AN1983. See


Application notes for other balanced mixers include: Mini Circuits
AN00001, AN00002, AN00003, Philips AN189, NS AN402,
70 2006-08-04 08:11:01 Frank Re: Question on how to use NE602
Hi Steve,

Excellent! I can see it now - I don't need to un-bias the oscillator
transistor. If I simply leave the AC output (pin 7) float, then there
is no feedback. I went over all the notes and data sheets one final
time and found the sole sentences that I had missed so many times. On
page four of the NE602 data sheet, "...external signal can be injected
at Pin 6 through a DC blocking capacitor. External LO should be at
least 200mVp-p."

That'll give me a good starting point. I'll vary the drive level and
see if there's an obvious level at which I get either lower distortion
or maximum conversion gain and call it good. Still no obvious way to
discern the input impedance, but that's easy to measure. Probably in
the kilohm range.



74 2006-08-05 15:28:22 Wes Hayward Re: Question on how to use NE602
Hi Frank, et al,

I did some measurements with a NE602 that are in the mixer chapter
(5) under "Some Practical Mixers." See p 5.10. This is not
everything that one would need to use the part, but just some of my
own measurements. The data sheet is still useful.

I also consider some examples for receivers using the NE602 in
Chapter 6 where we talked about dynamic range for a receiver and how
it can be calculated from parameters for a single stage. The NE602
example starts on page 6.30.

73, Wes