Double balanced mixer SA612A. Reference data
Encyclopedia of radio electronics and electrical engineering / Reference materials
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The SA612A (Philips Semiconductors) active dual balanced frequency mixer is designed for use in radio receivers operating in a frequency band up to 500 MHz. In addition to the mixer itself, the microcircuit contains a built-in local oscillator and voltage stabilization circuits.
The basis of the mixer is a balanced (differential) amplifier that provides an output signal that is proportional only to the difference between the signals at the inputs and does not depend on their absolute values, or on fluctuations in the supply voltage, or on changes in the ambient temperature [1].
The device is packaged in a plastic housing of two design options: DIP8 (SA612AN) - for traditional mounting (Fig. 1); S08 (SA612AD) - for surface (Fig. 2).
The block diagram of the SA612A balanced mixer is shown in Fig. 3. Pinout of the device: pins 1 and 2 - differential input of a balanced amplifier; pin 3 - common, negative power supply pin; pins 4 and 5 - differential mixer output; pins 6 and 7 - pins for connecting external local oscillator circuits: pin 8 - positive power pin.
As can be seen from the diagram, the device has two balanced inputs and outputs (hence the characteristic - double). This structure gives ample opportunities in the construction of the input and output circuits of the mixer (see below). In particular, the use of a balanced mixer circuit makes it possible to get rid of conversion by-products in the output signal [2].
Main technical characteristics at Tamb. av = 25 °C and supply voltage 6 V
- Supply voltage, V ...... 4,5 ... 8
- Current consumption, mA, maximum value......3
- typical value......2,4
- Maximum input signal frequency, MHz......500
- The maximum frequency of the built-in local oscillator, MHz ...... 200
- Noise figure, dB (typical value), at an input signal frequency of 45 MHz ...... 5
- Conversion coefficient, dB, at an input signal frequency of 45 MHz, the minimum value ...... 14
- typical value......17
- Intersection point for third-order intermodulation IIРЗ*. dBm (typical), with input power -45 dBm.....-13
- Input impedance of balanced inputs, kOhm (minimum value)......1,5
- Output impedance, kOhm (typical value) ...... 1,5
- Input capacitance, pF......3
- Working range of ambient temperature, °C. -40...+85
* This is the name of the conditional intersection point on the graph of a straight line characterizing the power of intermodulation distortions of the third order, with the continuation of the linear dynamic characteristic of the mixer [3]. This parameter allows you to estimate the dynamic range of the mixer from third-order intermodulation.
The indicated high-frequency parameters of the mixer were taken on a test bench, the scheme of which is shown in fig. 4. It can actually be considered as a typical switching circuit.
Depending on the specific application of the chip, the input signal may be applied in different ways. On fig. 5, a and b show the resonant variants of the input circuit, and in fig. 5,v - broadband (in this case, the unused pin must be “grounded” for alternating current with a capacitor with a capacity of 0,001...0,1 μF, depending on the operating frequency).
The mixer output signals (at pins 4 and 5) have opposite phases. The load can be switched on both between phases (Fig. 6, a) and single-phase (Fig. 6, b). The manufacturer allows the unused output to be left free; nevertheless, it is better to “ground” it too via alternating current through a capacitor.
As a frequency-setting element of the built-in local oscillator, you can use either an LC circuit (Fig. 7,a) or a quartz resonator (Fig. 7,6), operating at the fundamental frequency or harmonics. Paired with a harmonic resonator, it is necessary to use an additional LC circuit tuned to the frequency of the corresponding harmonic (L1C2C3, Fig. 7c). The ratings of external elements are determined from the same considerations as for a conventional local oscillator on a bipolar transistor. Pin 6 of the microcircuit is connected to the base of the internal transistor (VT1 in Fig. 7, a).
The mixer can also operate with an external local oscillator (Fig. 7d). The input voltage amplitude at pin 6 of the mixer should be within 200...300 mV.
If necessary, the local oscillator signal can be supplied to an external amplifier stage through a coupling capacitor C5 (Fig. 7a) of small capacity. The oscillation amplitude of the local oscillator will be greater if pin 7 of the mixer is shunted with a resistor (R1) with a resistance of 1...10 kOhm.
In Fig. Figures 8 and 9 show the temperature dependence of the noise figure Ksh of the mixer at various values of the supply voltage and input power corresponding to the "third-order intercept point" Pin. from respectively, and in Fig. 10 - dependence of the same parameter Рвх. from the supply voltage.
Literature
- Golovin O. V., Kubitsky A. A. Electronic amplifiers. - M.: Radio isvya', 1983, p. 87.
- Polyakov V. T. About the real selectivity of HF receivers. - Radio, 1981, No. 3, p. 18-21; No. 4, p. 21,22.
- Red E. T. Circuitry of radio receivers. - M.: Mir, 1989, p. eight.
- SA612A. Double-balanced mixer and oscillator Data sheet. - <8emlconductorB.phlllp8.com/acrobat/datasheetsSA612A.pdf>
Author: A.Temerev, Svetlovodsk, Kirovograd region, Ukraine
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Comments on the article:
ua9oas
Many years have passed since this thing was created. Although they say that it is noticeably better than our "PS1" (tell me how exactly?), But still, progress over the years in "mixer building" should also have gone far ahead. The most interesting and promising technology in such components is sige technology. Transistors and microcircuits based on it can have significantly better characteristics. But I cannot find such analogs, similar to the microcircuit presented here, on the net. Who can - help.
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