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SA612A Datasheet PDF : 19 Pages
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NXP Semiconductors
SA612A
Double-balanced mixer and oscillator
7. Functional description
The SA612A is a Gilbert cell, an oscillator/buffer, and a temperature-compensated bias
network as shown in Figure 3. The Gilbert cell is a differential amplifier (IN_A and IN_B
pins) that drives a balanced switching cell. The differential input stage provides gain and
determines the noise figure and signal handling performance of the system.
18 kΩ
6
7
25 kΩ
buffer
1.5 kΩ
4
1.5 kΩ
5
BIAS
BIAS
2
1
BIAS
1.5 kΩ
3
GND
1.5 kΩ
aaa-013205
Fig 3. Equivalent circuit
The SA612A is designed for optimum low-power performance. When used with the
SA614A as a 45 MHz cordless phone/cellular radio second IF and demodulator, the
SA612A is capable of receiving 119 dBm signals with a 12 dB S/N ratio. Third-order
intercept is typically 15 dBm (that is approximately +5 dBm output intercept because of
the RF gain). The system designer must be cognizant of this large signal limitation. When
designing LANs or other closed systems where transmission levels are high, and
small-signal or signal-to-noise issues are not critical, the input to the SA612A should be
appropriately scaled.
Besides excellent low-power performance well into VHF, the SA612A is flexible. The input,
output and oscillator ports support various configurations provided the designer
understands certain constraints, which are explained here.
The RF inputs (IN_A and IN_B pins) are biased internally. They are symmetrical. The
equivalent AC input impedance is approximately 1.5 k 3 pF through 50 MHz. IN_A and
IN_B pins can be used interchangeably, but they should not be DC biased externally.
Figure 4 shows three typical input configurations.
SA612A
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 3 — 4 June 2014
© NXP Semiconductors N.V. 2014. All rights reserved.
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