APPLICATION NOTE 286

The MAX2683 Low-Cost High-Performance 3.5GHz Upconverter


Abstract: This application note describes the features of the MAX2683 3.5GHz upconverter. A typical schematic is given with the matching components for 3.55GHz output, 1.6GHz LO and 350MHz input. The noise figure is ~12.5dB, and the conversion gain is 8.6dB. The integrated circuit (IC) can also be used for a downconverter. Links to tables of S-parameters are provided to aid the design engineer.

Additional Information:

Introduction

The MAX2683 is a double-balanced active mixer based on the Gilbert cell that is capable of accepting RF inputs up to 3.5GHz and producing IF outputs up to 3.6GHz. It features an adjustable bias control, conversion gain, insensitivity to mismatch, and superior isolation in a very compact format.

This application note presents a brief description of the mixer, design tips, and typical performance features for the MAX2683.

Upconverter Review

A fundamental property of mixers is frequency conversion. This property is put to use in virtually all transmitters. For typical operation, a modulating signal operating at a frequency of fMOD is injected into one port of the mixer, and a local oscillator (LO) signal at a frequency of fLO is injected into a second port. The resulting output radio frequency (RF) signal is upconverted to a frequency of fMOD + fLO. Frequency conversion results from a multiplication of the modulated fMOD waveform, cos(fMOD * t), and LO waveform. From trigonometry, we have the following:

Cos(fMOD * t) * cos(fLO * t) = 1/2 cos(fLO - fMOD) ± 1/2 cos(fLO ± fMOD)

In this ideal multiplication, the output of the mixer contains only signals at frequencies fLO- fMOD and fLO+ fMOD; that is, the original modulation signal fMOD and the local signal fLO are completely suppressed at the upconverter output RF port.

The Gilbert cell active mixer is based on an emitter-coupled-pair amplifier. The operation of this amplifier is best understood by dividing the modulated signal into its common-mode and differential-mode components. The modulated signal enters one side of the pair, while the opposite side is AC-grounded through a capacitor. From symmetry, the common-mode component shifts the current between the two branches and, for small signals, acts as a standard common-emitter amplifier. The MAX2683 employs four cross-coupled devices to the basic amplifier to multiply the modulated signal by ± at the LO rate and to achieve the desired double-balanced mixer characteristics. The combination of these devices with the emitter-coupled pair completes the basic Gilbert cell. As with the modulated signal input, the LO is injected in a single-ended fashion with the opposite side AC-grounded through a capacitor. The positive LO voltages cause the outer set of the device to be on, resulting in a multiplication of the modulated signal by ± at the LO rate, while negative voltages cause the inner pair to be on, also multiplying the modulated signal by ± at the LO rate.

Product Design and Performance Features

The MAX2683 operates from a single +2.7V to +5.5V supply. The device is available in an ultra-small 16-pin TSSOP-EP package with an exposed paddle for the special application up to 3.6GHz. It uses a double-balanced Gilbert cell architecture with single-ended RF and LO inputs and differential open-collector output ports. Differential output ports provide a wideband, flexible interface for either single-ended or differential applications. The MAX2683 features an adjustable bias control, set with an external resistor, that lets the user trade supply current for linearity to optimize system performance. A logic-level control enables an internal frequency doubler on this device, allowing the external local oscillator source to run at full or half frequency. An internal LO filter reduces LO harmonics and spurious mixing. Figure 1 is a simplified block diagram of a MAX2683 application.Figure 2 is a pin description of the MAX2683. The details of consequent performance features are described below.

Figure 1. Simplified block diagram of a MAX2683 application.
Figure 1. Simplified block diagram of a MAX2683 application.

Figure 2. Pin description of the MAX2683.
Figure 2. Pin description of the MAX2683.

DC Bias

The MAX2683 requires a DC bias. Whereas conventional passive mixers use AC signals to create device conduction, active Gilbert cell mixers require a DC power supply. DC bias is applied to the device in the form of a voltage VCC. Enough voltage must be applied to cause the transistors in the Gilbert cell to conduct, otherwise the desired switching action will not occur. The minimal voltage required for the mixer to operate is 2.7V. As VCC is increased, the simple bias scheme allows the transistors to turn on harder. The gain of the mixer increases, as does the compression point. Because change in bias affects linearity, such changes alter the levels of harmonic and spurious signals produced by the mixer. Bias changes also affect ft of the transistors in the chip and hence the frequency range over which the mixer operates. The linearity and supply current of the MAX2683 is externally programmable with a single resistor, BIAS, from BIAS to GND. A nominal resistor value of 1.2kΩ will set the supply current of 55mA. Decreasing the resistor value improves linearity at the cost of increasing the supply current. Increasing the resistor value decreases the supply current while degrading linearity. Use a resistor value in the range of 820Ω to 2.0kΩ.

Gain

The MAX2683 has conversion gain, so in conventional use the output signal will be at a higher power level than the input signal. Most of the gain in the MAX2683 comes from the emitter-coupled amplifier in the Gilbert cell. The amount of gain achieved will vary with the frequency, the temperature of the operation, the oscillator signal, and the bias level. In order to optimize the gain and the linearity, a properly designed PC board is an essential part of any RF/microwave circuit. Keep RF signal lines as short as possible to reduce losses, radiation, and inductance. Use separate, low inductance vias to the ground plane for each ground pin. For best performance, solder the exposed pad on the button of the device package to the board ground plane. The differential open-collector RFOUT- and RFOUT+ ports require external pullup inductors to VCC, as well as an output matching network for optimum gain performance. The S-parameters of modulated signal input, LO input, and RF output are shown in Table 2. Designers can refer to that table to develop optimized matching circuits to meet their system specifications.

Oscillator Signals

The MAX2683 requires low oscillator drive levels. In the mixer based on the Gilbert cell, the primary function of the LO signal is to switch the conduction path between the outer and inner transistors of the cross-coupled quad. This requires relatively little power. In general, the spurious response of a Gilbert cell mixer will improve at a lower oscillator drive level. Increasing the LO power to the MAX2683 upconverter will saturate (actually, "quasi-saturate") the transistors of the quad and emitter-coupled pair, and decrease linearity. As the LO drive level is decreased from a nominal characterization value, there is a 5dB to 10dB range over which conversion gain is not affected significantly. When the LO drive level is reduced still further, conversion gain will "roll off." No sinusoidal LO signals can have frequency components at many (harmonically related) frequencies. A typical LO input power is -5dBm at 50Ω matching for the MAX2683.

Operating Frequency Range

The MAX2683 operates over a very wide frequency range. It can operate as a downconverter or an upconverter. The frequency of the modulated signal through the Gilbert cell quad can go up to 3.8GHz. The output frequency range can reach 3.6GHz if a proper output matching network is provided. The MAX2683 features an internal LO frequency doubler that allows the external LO to run at full or half frequency. Running the LO at half frequency has the benefit of reducing unwanted LO leakage through the amplifier to the antenna. An internal LO band pass filter is integrated after the frequency doubler to help reduce LO harmonic content and spurious mixing. To enable the LO frequency doubler, drive ENX2 to a logic low level and connect the half-frequency external LO to the LOX2 port. To disable and bypass the LO frequency doubler and LO filter, drive ENX2 to a logic high level and connect the full-frequency external LO to the LOX1 port. Disabling the LO doubler has the benefit of reducing the supply current by 15mA. The maximum frequency range of LOX1 is up to 3.9GHz, and the LOX2 frequency range is up to 1.95GHz.

Noise Figure

The Gilbert cell structure is not a low-noise configuration. The mixer noise figure comes primarily from the shot noise of the four collector-cross-coupled transistors, the noise of both transistors in the emitter-coupled pair, and the thermal noise of both feedback resistors used with the emitter-coupled pair. The switching action of the LO can affect the mixer noise figure when there is very low input LO power. The typical noise figure of the MAX2683 is close to 12.5dB.

Matching Circuit

Three ports need to be matched properly in order to achieve optimum performance. Table 1 provides a complete S-parameter for three ports, the frequency range covered from 50MHz to 6GHz. The designer can refer to this table to choose the best matching circuit to meet system specifications. This application note includes an application schematic that shows a typical matching circuit for three ports. The input port is matched to 350MHz frequency, the LO port is matched to 1.6GHz, and the output port is matched to 3.55GHz.

Table 1. S-Parameters of the MAX2683

Table 1.1. F Input S11-Parameter
FREQ. 5VDC 5VDC 3.3VDC 3.3VDC   FREQ. 5VDC 5VDC 3.3VDC 3.3VDC
(MHz) Amplitude Degree Amplitude Degree   (MHz) Amplitude Degree Amplitude Degree
50 0.868 -4.4 0.868 -4.5   3050 0.566 -147.1 0.557 -154.6
100 0.851 -7.7 0.850 -7.9   3100 0.563 -147.5 0.555 -157.1
150 0.817 -13.9 0.813 -16.4   3150 0.562 -151.9 0.556 -159.2
200 0.801 -10.1 0.797 -11.6   3200 0.544 -154.3 0.559 -162.4
250 0.816 -11.8 0.814 -12.5   3250 0.568 -156.6 0.564 -164.7
300 0.831 -21.1 0.830 -22.5   3300 0.574 -160.0 0.572 -167.1
350 0.791 -22.4 0.789 -25.0   3350 0.583 -162.0 0.582 -169.4
400 0.770 -27.4 0.578 -30.0   3400 0.593 -164.0 0.592 -171.2
450 0.710 -27.2 0.639 -30.6   3450 0.604 -167.3 0.603 -174.2
500 0.715 -28.3 0.700 -29.9   3500 0.617 -169.1 0.616 -176.4
550 0.713 -30.8 0.701 -32.2   3550 0.631 -171.4 0.636 -178.7
600 0.705 -33.3 0.691 -34.8   3600 0.644 -173.8 0.644 179.0
650 0.698 -35.8 0.688 -37.5   3650 0.657 -176.2 0.656 176.3
700 0.690 -38.4 0.680 -40.1   3700 0.669 -178.8 0.665 173.5
750 0.682 -40.9 0.672 -42.6   3750 0.678 178.6 0.672 170.8
800 0.672 -43.1 0.662 -44.9   3800 0.685 175.8 0.677 168.1
850 0.665 -45.0 0.654 -47.0   3850 0.688 172.2 0.677 165.2
900 0.660 -47.0 0.648 -49.1   3900 0.689 170.1 0.674 162.0
950 0.654 -49.1 0.643 -51.3   3950 0.684 167.0 0.666 158.9
1000 0.651 -50.9 0.638 -52.0   4000 0.675 164.0 0.654 155.0
1050 0.635 -55.1 0.623 -58.0   4050 0.661 163.3 0.639 136.0
1100 0.635 -58.1 0.622 -61.5   4100 0.648 160.1 0.624 153.7
1150 0.633 -60.3 0.618 -63.6   4150 0.632 158.2 0.608 151.2
1200 0.631 -61.9 0.617 -65.6   4200 0.615 155.7 0.591 148.8
1250 0.631 -63.5 0.619 -67.1   4250 0.599 152.2 0.575 146.5
1300 0.633 -65.2 0.618 -68.6   4300 0.584 151.9 0.561 144.4
1350 0.633 -66.7 0.615 -70.4   4350 0.571 149.7 0.550 142.4
1400 0.630 -68.7 0.615 -72.4   4400 0.561 147.8 0.541 140.7
1450 0.630 -70.7 0.615 -74.5   4450 0.553 146.7 0.535 139.0
1500 0.630 -72.7 0.614 -76.5   4500 0.549 144.2 0.532 137.1
1550 0.629 -74.8 0.614 -78.1   4550 0.547 140.5 0.532 133.4
1600 0.627 -77.3 0.612 -81.0   4600 0.548 138.8 0.534 131.8
1650 0.622 -79.9 0.607 -82.2   4650 0.552 137.3 0.541 130.4
1700 0.619 -82.5 0.604 -85.9   4700 0.558 135.9 0.548 129.1
1750 0.618 -85.0 0.604 -89.4   4750 0.566 134.4 0.556 127.5
1800 0.618 -87.6 0.605 -92.1   4800 0.577 133.1 0.569 126.2
1850 0.616 -90.5 0.604 -95.0   4850 0.589 131.7 0.581 124.9
1900 0.615 -93.3 0.602 -98.2   4900 0.604 130.4 0.595 123.6
1950 0.612 -96.0 0.600 -101.0   4950 0.616 128.9 0.607 122.1
2000 0.612 -98.7 0.601 -103.2   5000 0.628 127.3 0.619 120.4
2050 0.609 -96.7 0.600 -100.9   5050 0.671 127.8 0.644 120.9
2100 0.614 -98.1 0.605 -102.6   5100 0.660 127.9 0.644 121.2
2150 0.620 -100.0 0.613 -105.1   5150 0.663 127.7 0.647 121.1
2200 0.626 -102.0 0.618 -107.5   5200 0.668 127.2 0.651 120.1
2250 0.634 -105.1 0.626 -109.9   5250 0.671 126.2 0.654 119.4
2300 0.640 -107.5 0.632 -112.4   5300 0.674 124.3 0.653 117.9
2350 0.644 -110.1 0.636 -115.1   5350 0.672 123.1 0.650 116.1
2400 0.647 -112.2 0.636 -118.1   5400 0.668 121.4 0.644 114.3
2450 0.642 -115.0 0.634 -121.0   5450 0.659 119.4 0.632 112.4
2500 0.645 -116.7 0.632 -123.9   5500 0.647 117.7 0.618 110.9
2550 0.642 -119.3 0.626 -126.7   5550 0.633 116.4 0.603 108.0
2600 0.636 -122.0 0.616 -129.5   5600 0.620 114.6 0.591 107.4
2650 0.627 -124.4 0.604 -132.1   5650 0.608 113.1 0.581 106.5
2700 0.616 -127.1 0.596 -134.3   5700 0.598 111.4 0.572 105.2
2750 0.608 -129.2 0.590 -136.4   5750 0.587 109.6 0.563 103.3
2800 0.600 -131.1 0.584 -138.8   5800 0.577 108.1 0.554 101.4
2850 0.592 -134.2 0.577 -141.4   5850 0.569 106.2 0.547 99.9
2900 0.583 -136.7 0.569 -144.1   5900 0.562 105.1 0.541 98.5
2950 0.576 -139.2 0.562 -146.7   5950 0.556 103.0 0.557 97.1
3000 0.570 -141.7 0.558 -149.2   6000 0.551 102.1 0.553 96.0

Table 1.2. LOX1 Input S11-Parameter
FREQ. 5VDC 5VDC 3.3VDC 3.3VDC   FREQ. 5VDC 5VDC 3.3VDC 3.3VDC
(MHz) Amplitude Degree Amplitude Degree   (MHz) Amplitude Degree Amplitude Degree
50 0.648 -30.3 0.648 -30.4   3050 0.155 173.0 0.162 170.5
100 0.460 -33.8 0.459 -39.9   3100 0.157 169.0 0.164 165.7
150 0.382 -32.2 0.381 -32.2   3150 0.159 165.0 0.167 161.5
200 0.343 -30.7 0.342 -30.7   3200 0.162 161.0 0.169 157.7
250 0.318 -29.8 0.318 -29.0   3250 0.165 158.0 0.173 154.4
300 0.301 -29.6 0.300 -29.8   3300 0.168 155.0 0.175 151.6
350 0.287 -30.0 0.287 -30.2   3350 0.171 152.0 0.177 149.5
400 0.276 -30.7 0.276 -30.9   3400 0.173 150.0 0.179 147.7
450 0.266 -30.7 0.267 -32.1   3450 0.173 149.0 0.178 146.1
500 0.260 -33.3 0.261 33.6   3500 0.172 147.0 0.177 144.8
550 0.260 -33.3 0.261 -33.6   3550 0.170 146.0 0.174 143.6
600 0.255 -35.1 0.250 -37.0   3600 0.167 145.0 0.171 142.9
650 0.250 -37.0 0.248 -39.4   3650 0.162 145.0 0.166 142.4
700 0.245 -41.1 0.245 -41.5   3700 0.155 145.0 0.160 142.1
750 0.244 -43.4 0.245 -43.8   3750 0.148 144.0 0.152 141.9
800 0.244 -45.6 0.245 -46.1   3800 0.140 144.0 0.143 141.2
850 0.250 -47.7 0.246 -48.3   3850 0.131 144.0 0.134 141.4
900 0.245 -50.0 0.247 -50.7   3900 0.122 144.0 0.126 140.5
950 0.246 -52.3 0.247 -53.3   3950 0.112 143.0 0.116 139.4
1000 0.246 -54.7 0.246 -55.0   4000 0.102 142.0 0.106 137.9
1050 0.242 -59.1 0.242 -60.5   4050 0.100 142.0 0.104 138.4
1100 0.240 -61.5 0.240 -62.3   4100 0.091 141.0 0.095 137.1
1150 0.238 -63.1 0.238 -63.9   4150 0.083 139.0 0.087 135.1
1200 0.235 -64.7 0.236 -65.5   4200 0.074 138.0 0.079 132.5
1250 0.233 -66.2 0.233 -67.1   4250 0.067 135.0 0.071 129.8
1300 0.230 -68.0 0.230 -68.9   4300 0.060 133.0 0.065 126.7
1350 0.226 -69.7 0.226 -70.5   4350 0.055 129.0 0.060 123.0
1400 0.222 -71.5 0.222 -72.5   4400 0.050 126.0 0.055 119.1
1450 0.218 -73.6 0.218 -74.6   4450 0.046 123.0 0.051 116.3
1500 0.214 -75.9 0.214 -77.0   4500 0.045 123.0 0.050 115.8
1550 0.209 -78.4 0.211 -79.5   4550 0.045 124.0 0.050 117.2
1600 0.205 -81.1 0.207 -82.2   4600 0.047 126.0 0.053 118.8
1650 0.202 -84.0 0.204 -85.2   4650 0.053 128.0 0.058 121.2
1700 0.199 -87.1 0.200 -88.4   4700 0.060 129.0 0.064 122.7
1750 0.197 -90.5 0.199 -91.9   4750 0.068 130.0 0.072 123.9
1800 0.195 -94.0 0.197 -95.4   4800 0.076 130.0 0.064 122.5
1850 0.195 -97.4 0.197 -99.0   4850 0.083 130.0 0.086 125.3
1900 0.195 -97.5 0.197 -102.4   4900 0.091 131.0 0.094 126.4
1950 0.194 -101.0 0.195 -106.6   4950 0.099 132.0 0.102 127.6
2000 0.193 -105.0 0.195 -109.5   5000 0.100 133.0 0.111 128.6
2050 0.196 -110.0 0.199 -111.4   5050 0.122 132.0 0.125 128.0
2100 0.199 -112.0 0.202 -113.7   5100 0.129 132.0 0.131 128.0
2150 0.201 -114.0 0.204 -116.0   5150 0.134 133.0 0.137 129.4
2200 0.202 -116.0 0.206 -128.1   5200 0.139 133.0 0.142 129.2
2250 0.204 -118.0 0.208 -120.0   5250 0.142 133.0 0.144 128.5
2300 0.205 -120.0 0.209 -122.0   5300 0.144 132.0 0.146 127.4
2350 0.205 -122.0 0.209 -123.8   5350 0.144 130.0 0.146 125.5
2400 0.204 -123.0 0.208 -125.1   5400 0.141 127.0 0.142 123.2
2450 0.202 -125.0 0.206 -127.4   5450 0.136 125.0 0.137 120.1
2500 0.200 -127.0 0.204 -129.7   5500 0.129 122.0 0.131 116.5
2550 0.197 -129.0 0.202 -132.4   5550 0.121 1118.0 0.121 112.9
2600 0.193 -132.0 0.198 -135.7   5600 0.110 113.0 0.117 106.4
2650 0.189 -136.0 0.193 -139.6   5650 0.098 106.0 0.100 99.3
2700 0.183 -141.0 0.187 -144.4   5700 0.088 99.0 0.091 190.9
2750 0.175 -146.0 0.179 -149.4   5750 0.079 189.0 0.083 181.1
2800 0.168 -151.0 0.172 -154.6   5800 0.070 78.0 0.076 169.3
2850 0.162 -156.0 0.167 -159.9   5850 0.065 63.0 0.073 155.9
2900 0.157 -161.0 0.163 -165.1   5900 0.063 49.0 0.073 142.0
2950 0.155 -167.0 0.161 -170.9   5950 0.064 33.0 0.075 28.5
3000 0.153 -173.0 0.160 -176.7   6000 0.067 18.0 0.079 16.1

Table 1.3. LOX2 Input S11-Parameter
FREQ. 5VDC 5VDC 3.3VDC 3.3VDC   FREQ. 5VDC 5VDC 3.3VDC 3.3VDC
(MHz) Amplitude Degree Amplitude Degree   (MHz) Amplitude Degree Amplitude Degree
50 0.756 -18.6 0.775 -19.6   1550 0.304 -92.1 0.306 -93.3
100 0.619 -26.4 0.625 -27.2   1600 0.301 -94.5 0.304 -95.7
150 0.537 -29.1 0.599 -29.7   1650 0.299 -97.1 0.303 -98.4
200 0.488 -30.7 0.489 -31.2   1700 0.299 -99.8 0.302 -101.1
250 0.455 -32.2 0.456 -32.7   1750 0.298 -102.3 0.300 -103.9
300 0.431 -34.1 0.432 -34.5   1800 0.298 -105.4 0.301 -106.7
350 0.411 -35.1 0.413 -36.6   1850 0.299 -108.1 0.301 -109.5
400 0.395 -38.4 0.397 -38.8   1900 0.299 -110.8 0.303 -112.2
450 0.382 -40.8 0.382 -41.3   1950 0.302 -113.4 0.305 -114.7
500 0.370 -43.4 0.372 -43.9   2000 0.303 -115.9 0.307 -117.4
550 0.362 -46.1 0.362 -46.6   2050 0.310 -117.1 0.314 -118.6
600 0.354 -48.8 0.355 -49.4   2100 0.315 -119.2 0.319 -120.7
650 0.348 -51.6 0.349 -52.2   2150 0.305 -115.0 0.324 -122.7
700 0.344 -54.3 0.345 -55.9   2200 0.324 -123.0 0.329 -124.6
750 0.341 -57.1 0.342 -57.9   2250 0.327 -124.8 0.332 -126.4
800 0.338 -59.9 0.340 -60.5   2300 0.330 -126.5 0.335 -128.2
850 0.337 -62.4 0.337 -632.0   2350 0.334 -128.1 0.327 -129.9
900 0.335 -65.0 0.336 -65.7   2400 0.335 -129.7 0.339 -131.4
950 0.332 -67.3 0.334 -68.0   2450 0.335 -131.4 0.337 -133.2
1000 0.331 -69.4 0.332 -70.2   2500 0.333 -133.1 0.336 -137.9
1050 0.326 -72.1 0.327 -73.4   2550 0.330 -134.7 0.333 -136.7
1100 0.325 -74.6 0.325 -75.6   2600 0.325 -136.8 0.330 -138.7
1150 0.323 -76.3 0.325 -77.1   2650 0.319 -138.8 0.323 -140.8
1200 0.322 -78.1 0.323 -78.9   2700 0.312 -140.7 0.316 -142.9
1250 0.319 -79.8 0.321 -80.7   2750 0.305 -142.6 0.309 -144.9
1300 0.316 -81.5 0.318 -82.5   2800 0.299 -144.7 0.303 -146.0
1350 0.327 -71.1 0.315 -84.4   2850 0.295 -146.9 0.298 -147.1
1400 0.312 -85.4 0.313 -83.4   2900 0.291 -149.1 0.293 -151.4
1450 0.308 -87.4 0.311 -88.5   2950 0.287 -151.4 0.289 -153.7
1500 0.306 -89.7 0.309 -90.9   3000 0.285 -153.6 0.287 -156.0

Table 1.4. Up converter output S22-Parameter
FREQ. 5VDC 5VDC 3.3VDC 3.3VDC   FREQ. 5VDC 5VDC 3.3VDC 3.3VDC
(MHz) Amplitude Degree Amplitude Degree   (MHz) Amplitude Degree Amplitude Degree
50 0.883 -6.1 0.912 -6.9   3050 0.739 129.7 0.738 129.6
100 0.962 -11.1 0.883 -11.5   3100 0.729 126.8 0.729 126.8
150 0.838 -14.6 0.857 -14.7   3150 0.710 124.5 0.711 124.7
200 0.827 -16.5 0.845 -16.5   3200 0.686 122.6 0.687 122.8
250 0.841 -17.6 0.859 -18.3   3250 0.654 120.8 0.657 121.1
300 0.854 -20.3 0.871 -21.1   3300 0.620 119.0 0.625 119.4
350 0.863 -23.0 0.878 -24.2   3350 0.589 116.8 0.595 117.4
400 0.863 -26.4 0.877 -27.3   3400 0.564 114.6 0.570 115.0
450 0.858 -29.7 0.872 -30.7   3450 0.543 111.7 0.551 112.2
500 0.851 -33.3 0.864 -34.3   3500 0.532 108.6 0.541 109.1
550 0.841 -37.6 0.853 -38.7   3550 0.530 105.6 0.541 106.2
600 0.827 -42.4 0.840 -43.6   3600 0.539 103.6 0.550 103.8
650 0.812 -47.8 0.825 -49.1   3650 0.558 101.0 0.570 101.8
700 0.793 -53.7 0.807 -55.2   3700 0.583 99.9 0.597 100.5
750 0.774 -59.7 0.787 -61.6   3750 0.613 99.4 0.628 99.9
800 0.756 -65.6 0.762 -67.7   3800 0.644 99.4 0.660 99.8
850 0.739 -71.0 0.737 -73.1   3850 0.672 99.7 0.690 99.9
900 0.723 -75.7 0.714 -77.1   3900 0.694 100.4 0.713 100.2
950 0.709 -79.1 0.700 -79.9   3950 0.707 100.1 0.726 100.3
1000 0.712 -83.3 0.715 -83.7   4000 0.706 100.5 0.725 100.3
1050 0.715 -87.0 0.711 -87.6   4050 0.690 103.2 0.709 102.8
1100 0.718 -89.3 0.717 -89.4   4100 0.667 102.9 0.686 102.3
1150 0.723 -91.1 0.723 -91.0   4150 0.635 101.9 0.623 101.2
1200 0.725 -93.0 0.727 -93.2   4200 0.599 100.1 0.615 99.3
1250 0.723 -95.4 0.726 -95.6   4250 0.563 97.3 0.578 96.2
1300 0.715 -98.1 0.720 -98.3   4300 0.531 93.2 0.547 92.0
1350 0.702 -101.0 0.708 -101.0   4350 0.512 87.8 0.527 86.7
1400 0.684 -104.6 0.691 -104.0   4400 0.505 81.7 0.521 80.6
1450 0.661 -108.6 0.669 -109.0   4450 0.511 75.7 0.527 74.7
1500 0.633 -112.8 0.642 -113.0   4500 0.532 70.8 0.547 69.8
1550 0.692 -116.9 0.621 -117.3   4550 0.562 57.3 0.576 86.4
1600 0.594 -121.7 0.609 -122.2   4600 0.594 65.3 0.609 64.4
1650 0.577 -126.5 0.589 -127.0   4650 0.627 64.4 0.641 63.6
1700 0.569 -130.9 0.581 -131.6   4700 0.656 64.7 0.669 63.9
1750 0.567 -135.5 0.581 -136.1   4750 0.677 66.0 0.689 65.2
1800 0.571 -140.1 0.585 -140.7   4800 0.694 67.7 0.705 67.0
1850 0.580 -144.0 0.595 -144.9   4850 0.703 69.8 0.711 69.0
1900 0.592 -148.2 0.607 -148.9   4900 0.706 71.9 0.715 71.1
1950 0.608 -151.0 0.623 -152.6   4950 0.702 73.6 0.710 72.8
2000 0.624 -155.0 0.639 -156.9   5000 0.691 75.0 0.699 74.2
2050 0.651 -156.0 0.667 -157.7   5050 0.697 77.1 0.705 76.3
2100 0.674 -166.5 0.689 -151.3   5100 0.694 76.8 0.702 75.7
2150 0.689 -163.5 0.704 -167.7   5150 0.684 74.5 0.692 73.6
2200 0.704 -166.7 0.717 -167.8   5200 0.665 70.8 0.673 69.7
2250 0.711 -170.3 0.723 -171.5   5250 0.644 65.9 0.651 64.7
2300 0.703 -174.0 0.714 -175.2   5300 0.624 60.2 0.631 59.0
2350 0.687 -177.0 0.695 -178.4   5350 0.607 54.3 0.613 53.9
2400 0.669 -179.9 0.677 178.6   5400 0.592 48.9 0.598 47.5
2450 0.647 176.0 0.652 175.3   5450 0.581 44.5 0.585 43.3
2500 0.622 173.6 0.627 172.3   5500 0.573 41.7 0.578 40.5
2550 0.604 170.5 0.609 169.2   5550 0.569 40.3 0.574 39.1
2600 0.592 166.9 0.597 165.6   5600 0.567 39.7 0.570 38.6
2650 0.589 163.0 0.593 161.7   5650 0.565 40.1 0.569 39.1
2700 0.594 158.8 0.590 157.7   5700 0.565 41.2 0.568 40.2
2750 0.609 154.4 0.612 153.4   5750 0.566 42.6 0.569 41.7
2800 0.631 149.9 0.634 149.0   5800 0.570 43.7 0.572 42.9
2850 0.656 145.3 0.658 144.6   5850 0.576 45.1 0.580 44.3
2900 0.682 141.4 0.683 140.8   5900 0.583 46.0 0.586 45.5
2950 0.709 137.6 0.710 137.2   5950 0.597 47.0 0.595 46.3
3000 0.729 133.9 0.728 133.6   6000 0.605 47.4 0.609 46.7

Linearity and Dynamic Range

The Gilbert cell structure does not yield a mixer with a high dynamic range. The following two equations describe linear dynamic range and spurious free dynamic range:

Linear dynamic range = P1dB - [NF + G + 3dB -114 dBm + 10 log10(BW)]
Spurious free dynamic range = 2/3 [IP3 - G - NF -10 log10(BW) + 114 dBm]

where P1dB is the output power of the mixer at 1dB gain compression (in dBm), NF is the noise figure of the mixer (in dB), G is the conversion gain of the mixer (in dB), BW is the bandwidth of the mixer (in dB), and IP3 is the output third-order interception point (in dB). These equations show that dynamic range is a function of noise figure, output compression point, interception point, and gain. Because the MAX2683 has moderate dB conversion gain, its dynamic range is not very low. The linearity of the MAX2683 is externally programmable with a single resistor. Increasing or decreasing that bias-resistor value will change the linearity performance of the MAX2683. There is a trade-off between linearity and supply current when the value of the bias resistor is changed.

Typical Application

Figure 3 shows a typical upconverter application circuit. As depicted in the figure, the mixer is a multiplier based on the Gilbert cell with an RF input amplifier. Double-balanced mixers such as this offer good port-to-port isolation and low LO free through at the output. RF output port input is configured for differential operation. However, the RF input and LO input can be driven in a single-ended operation. The LO and RF input are 50Ω. The mixer output requires an external matching network to convert high output impedance into lower impedance to meet system requirements. A balun or impedance matching transformer is required for such impedance transform and differential to single-ended transform. The test data of that application circuit is shown in Table 2.

Figure 3. Application Schematic of the MAX2683.
Figure 3. Application Schematic of the MAX2683.

Table 2. Test Data of a MAX2683 Application

(Test conditions: VCC = +5.0V, RBIAS = 1.2kΩ, /ENX2\ = GND, fRFIN = 350MHz, PRFIN = -20dBm, fLO = 1600MHz, PLO = -5dBm; all input/output ports terminated in 50Ω; RFOUT+ and RFOUT- matched to single-ended 50Ω load; TA = +25°C, unless otherwise noted.)

PARAMETER CONDITIONS TESTED UNITS
Input Frequency Range Note 1 350 MHz
RF Output Frequency Range Note 1 3.55 GHz
LOX2 Frequency Range   1.6 GHz
LOX1 Frequency Range   N/A GHz
Conversion Gain fLOX2 = 1600MHz, fRFOUT = 3.55GHz, VCC = +5V 8.6 dB
Gain Variation over Temperature TA = -40°C to +85°C, VCC = +5V TBD dB
Input 1dB Compression Point fLOX2 = 1600MHz, fRFOUT = 3.55GHz, VCC = +5V -6 dBm
Input Third-Order Intercept Point fLOX2 = 1600MHz, fRFOUT = 3.55GHz, VCC = +5V, Note 2 +1.3 dBm
Input Second-Order Intercept Point fLOX2 = 1600MHz, fRFOUT = 3.55GHz, VCC = +5V +42.6 dBm
Noise Figure   TBD dB
RFIN Input Return Loss At 350 MHz <-20 dB
LOX2 Leakage at RFIN /ENX2\ = GND fRFIN = 1 x fLO -42 dBm
fRFIN = 2 x fLO -38
fRFIN = 3 x fLO -49
LOX1 Leakage at RFIN /ENX2\ = Vcc fRFOUT = 1 x fLO N/A dBm
LOX2 Leakage at IFOUT+, RFOUT- /ENX2\ = GND fRFOUT = 1 x fLO -32.7 dBm
fRFOUT = 2 x fLO -16.4
fRFOUT = 3 x fLO -53.1
LOX1 Leakage at IFOUT+, RFOUT- /ENX2\ = Vcc fRFOUT = 1 x fLO -39 dBm
LOX1, LOX2 Input Return Loss   -18 dB

Notes

Note 1. The device has been fully characterized at this specified frequency range. Operation outside this range is possible but not guaranteed.
Note 2. IIP3 is measured with two tones at 350MHz and 351MHz, -20dBm per tone, fRFLO = 1.6GHz.
Note 3. IIP2 is measured with fRFIIN = 350MHz, PRFIN = -20dBm, fLO = 1.6GHz.
Note 4. The input match is optimized for best return loss at fRFIIN = 350MHz.


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APP 286:
APPLICATION NOTE 286,AN286, AN 286, APP286, Appnote286, Appnote 286