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NE162 mixer: input/output impedance in balanced mode?

S

sparks

Jan 1, 1970
0
Hi,
Could someone please clarify the input and output impedance
requirements when using the NE162 in a balanced configuration - that
is using a balanced transformer at the input (pins1&2) and output
(pins 4&5).
The datasheet mentions 1.5K impedance at each input and output
terminal, but does this mean a transformer would need to step up a 50
ohm unbalanced source to 3K ohms (balanced) to feed the two input
pins, and vice versa to step the output down to 50 ohms. Ive seen
circuits on the Net which imply the high impedance winding of both
transformers was 1.5K and another circuit that implies a 3K ohm centre
tapped winding where the CT goes to Vcc on the O/P transformer. All a
bit confusing...
thanks,
JEFF
 
A

Andrew Holme

Jan 1, 1970
0
sparks said:
Hi,
Could someone please clarify the input and output impedance
requirements when using the NE162 in a balanced configuration - that
is using a balanced transformer at the input (pins1&2) and output
(pins 4&5).
The datasheet mentions 1.5K impedance at each input and output
terminal, but does this mean a transformer would need to step up a 50
ohm unbalanced source to 3K ohms (balanced) to feed the two input
pins, and vice versa to step the output down to 50 ohms. Ive seen
circuits on the Net which imply the high impedance winding of both
transformers was 1.5K and another circuit that implies a 3K ohm centre
tapped winding where the CT goes to Vcc on the O/P transformer. All a
bit confusing...
thanks,
JEFF

The device numbers are NE602, NE612, SA602, SA612.

Each input looks like 1k5 || 3pF. The differential input impedance is 3k.

The single-ended output impedance at pin 4 or pin 5 is 1k5 and the
differential output impedance is 3k.

The output transformer CT need not be connected to Vcc.

Here's an unbalanced input matching simulation for LTSpice:

Version 4
SHEET 1 880 680
WIRE 208 32 96 32
WIRE 608 32 208 32
WIRE 96 48 96 32
WIRE 208 80 208 32
WIRE -96 144 -208 144
WIRE 96 144 96 112
WIRE 96 144 -16 144
WIRE 96 176 96 144
WIRE 208 224 208 160
WIRE 368 224 208 224
WIRE 480 224 368 224
WIRE 608 224 608 32
WIRE 736 224 608 224
WIRE -208 240 -208 144
WIRE 368 240 368 224
WIRE 480 240 480 224
WIRE 608 240 608 224
WIRE 736 240 736 224
WIRE 96 272 96 240
WIRE 208 272 208 224
WIRE 208 272 96 272
WIRE 208 288 208 272
WIRE 368 336 368 320
WIRE 480 336 480 304
WIRE 608 336 608 320
WIRE 736 336 736 304
WIRE -208 352 -208 320
WIRE 208 384 208 352
FLAG -208 352 0
FLAG 368 336 0
FLAG 608 336 0
FLAG 208 384 0
FLAG 480 336 0
FLAG 736 336 0
SYMBOL ind 192 64 R0
SYMATTR InstName L1
SYMATTR Value 290n
SYMATTR SpiceLine Rser=1
SYMBOL cap 80 48 R0
SYMATTR InstName C1
SYMATTR Value 47p
SYMBOL cap 80 176 R0
SYMATTR InstName C2
SYMATTR Value 220p
SYMBOL cap 192 288 R0
SYMATTR InstName C3
SYMATTR Value 100n
SYMBOL res 352 224 R0
SYMATTR InstName R1
SYMATTR Value 1k5
SYMBOL res 592 224 R0
SYMATTR InstName R2
SYMATTR Value 1k5
SYMBOL res 0 128 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R3
SYMATTR Value 50
SYMBOL voltage -208 224 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value SINE(0 1m 45e6)
SYMBOL cap 720 240 R0
SYMATTR InstName C4
SYMATTR Value 3p
SYMBOL cap 464 240 R0
SYMATTR InstName C5
SYMATTR Value 3p
TEXT 358 120 Left 0 !.tran 1u
 
S

sparks

Jan 1, 1970
0
Thanks Andrew for your help (again).
That clarifies if for me.
regards from 'down under",
JEFF
 
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