LT5546 40MHz to 500MHz VGA and I/Q Demodulator with 17MHz Baseband Bandwidth U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO 17MHz I/Q Lowpass Output Noise Filters Wide Range 1.8V to 5.25V Supply Voltage Frequency Range: 40MHz to 500MHz THD < 0.14% (–57dBc) at 800mVP-P Differential Output Level IF Overload Detector Log Linear Gain Control Range: –7dB to 56dB Baseband I/Q Amplitude Imbalance: 0.2dB Baseband I/Q Phase Imbalance: 0.6° 7.8dB Noise Figure at Max Gain Input IP3 at Low Gain: – 1dBm Low Supply Current: 24mA Low Delay Shift Over Gain Control Range: 2ps/dB Outputs Biased Up While in Standby 16-Lead QFN 4mm × 4mm Package with Exposed Pad U APPLICATIO S ■ ■ ■ GPS IF Receivers Satellite IF Receivers VHF/UHF Receivers Wireless Local Loop , LTC and LT are registered trademarks of Linear Technology Corporation. U ■ The LT®5546 is a 40MHz to 500MHz monolithic integrated quadrature demodulator with variable gain amplifier (VGA) and 17MHz I/Q baseband bandwidth designed for low voltage operation. It supports standards that use a linear modulation format. The chip consists of a VGA, quadrature downconverting mixers and 17MHz lowpass noise filters (LPF). The LO port consists of a divide-by-two stage and LO buffers. The IC provides all building blocks for IF downconversion to I and Q baseband signals with a single supply voltage of 1.8V to 5.25V. The VGA gain has a linearin-dB relationship to the control input voltage. Hard-clipping amplifiers at the mixer outputs reduce the recovery time from a signal overload condition. The lowpass filters reduce the out-of-band noise and spurious frequency components. The –3dB corner frequency of the noise filters is approximately 17MHz and has a first order rolloff. The standby mode provides reduced supply current and fast transient response into the normal operating mode when the I/Q outputs are AC-coupled to a baseband chip. TYPICAL APPLICATIO C2 1µF IF + L1 15nH C3 10pF L2 15nH C1 1nF VCC IF –30 IOUT+ – –35 IF DET VCTRL 2xLO + C5 3.3pF –25 IOUT– GAIN CONTROL 2xLO C4 560MHz 3.3pF INPUT Total Harmonic Distortion vs IF Input Level at 1.8V Supply 1.8V QOUT+ C3 1.8pF THD (dBc) 280MHz IF INPUT fIF, 1 = 280MHz fIF, 2 = 280.1MHz f2xLO = 570MHz 800mVP-P DIFFERENTIAL OUT –40 –45 –50 L3 39nH ÷2 QOUT– 2xLO – EN STBY GND LT5546 5546 TA01 ENABLE STANDBY –55 –60 –60 –40 –30 –20 –50 IF INPUT POWER EACH TONE (dBm) –10 5546 TA01b 5546f 1 LT5546 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART NUMBER QOUT– QOUT+ IOUT+ IOUT– TOP VIEW Supply Voltage ....................................................... 5.5V Differential Voltage Between 2xLO+ and 2xLO– .......... 4V IF+, IF– ............................................. –500mV to 500mV IOUT+, IOUT–, QOUT+, QOUT– .................. VCC – 1.8V to VCC Operating Ambient Temperature (Note 2) ...................................................–40°C to 85°C Storage Temperature Range ..................–65°C to 125°C Voltage on Any Pin Not to Exceed ........................ –500mV to VCC + 500mV 16 15 14 13 GND 1 LT5546EUF 12 STBY IF+ 2 11 2xLO+ 17 IF – 3 10 2xLO– GND 4 6 7 8 VCC VCTRL IF DET VCC 9 5 EN UF PART MARKING 5546 UF PACKAGE 16-LEAD (4mm × 4mm) PLASTIC QFN TJMAX = 125°C, θJA = 37°C/W EXPOSED PAD IS GND (PIN 17) (MUST BE SOLDERED TO PCB) Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS VCC = 3V, f2xLO = 570MHz, P2xLO = –5dBm (Note 5), f IF = 284MHz, PIF = –30dBm, I and Q outputs 800mVP-P into 4kΩ differential load, TA = 25°C, EN = VCC, STBY = VCC, unless otherwise noted. (Note 3) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS IF Input fIF Frequency Range 40 to 500 MHz Nominal Input Level RSOURCE = 200Ω Differential –76 to –19 dBm Input Impedance IF+, IF– to GND, EN = VCC IF+, IF– to GND, EN = GND 100Ω//1.2pF 1pF NF Noise Figure at Max Gain VCTRL = 1.7V 7.8 GL Min Gain (Note 4) VCTRL = 0.2V 1.6 49 dB 6 dB GH Max Gain (Note 4) VCTRL = 1.7V 56 dB IIP3 Input IP3, Min Gain Input IP3, Max Gain PIF = –22.5dBm (Note 7) PIF = –75dBm (Note 7) –1 –49 dBm dBm IIP2 Input IP2, Min Gain Input IP2, Max Gain VCTRL = 0.2V (Note 9) VCTRL = 1.7V (Note 9) 36 –25 dBm dBm Nominal Voltage Swing (Note 6) 0.8 VP-P Clipping Level (Note 6) 1.47 VP-P Demodulator I/Q Output DC Common Mode Voltage I/Q Amplitude Imbalance ro VCC – 1.19 V (Note 8) 0.14 0.6 dB I/Q Phase Imbalance (Note 8) 0.6 3 Deg DC Offset (Notes 6, 8) 21 mV Output Driving Capability Single Ended, CLOAD ≤ 10pF 1.5 kΩ Small-Signal Output Impedance (Note 6) 2 180 Ω STBY to Turn-On Delay 0.3 µs I/Q Output 1dB Compression –10 dBm – 49 dBc I/Q Output IM3 PIF, 1 = –25.5dBm, 280MHz PIF, 2 = –25.5dBm, 280.1MHz (Note 7) 5546f 2 LT5546 ELECTRICAL CHARACTERISTICS VCC = 3V, f2×LO = 570MHz, P2×LO = –5dBm (Note 5), f IF = 284MHz, PIF = –30dBm, I and Q outputs 800mVP-P into 4kΩ differential load, TA = 25°C, EN = VCC, STBY = VCC, unless otherwise noted. (Note 3) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Variable Gain Amplifier (VGA) Gain Slope Linearity Error VCTRL = 0V to 1.4V ±0.5 dB Temperature Gain Shift T = –40°C to 85°C, VCTRL = 0V to 1.4V ±0.4 dB Gain Control Response Time Settled within 10% of Final Value 90 ns 0 to 1.7 V Gain Control Voltage Range Gain Control Slope 41 dB/V Gain Control Input Impedance To Internal 0.2V Reference 25 kΩ Delay Shift Over Gain Control Measured Over 10dB Step 2 ps/dB 17 MHz Amplitude Roll-Off at 50MHz –9 dB Group Delay Ripple 1 ns Baseband Lowpass Filter (LPF) –3dB Cutoff Frequency 13 2xLO Input f2xLO Frequency Range P2xLO Input Power 1:2 Transformer with 240Ω Shunt Resistor (Note 5) Input Power LC Balun (Note 5) Input Impedance Differential Between 2xLO+ and 2xLO– –20 80 to 1000 MHz –5 dBm –10 dBm 800Ω//0.4pF DC Common Mode Voltage VCC – 0.4 V –30 to 8 dBm IF Detector IF Detector Range Referred to IF Input Output Voltage Range For PIF = –30dBm to 8dBm Detector Response Time With External 1.8pF Load, Settling within 10% of Final Value 0.27 to 1.2 V 80 ns Power Supply VCC Supply Voltage 1.8 5.25 V ICC Supply Current EN = High, STBY = Low or High 24 34 mA IOFF Shutdown Current EN, STBY < 350mV 0.2 30 µA ISTBY Standby Current EN = Low; STBY = High 3.6 6 mA Enable Enable Pin Voltage EN = High Disable Enable Pin Voltage EN = Low Standby Standby Pin Voltage STBY = High No Standby Standby Pin Voltage STBY = Low Mode Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Specifications over the –40°C to 85°C temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Tests are performed as shown in the configuration of Figure 6. The IF input transformer loss is substracted from the measured values. Note 4: Power gain is defined here as the I (or Q) output power into a 4kΩ differential load, divided by the IF input power in dB. To calculate the voltage gain between the differential I output (or Q output) and the IF input, including ideal matching network, 10 • log(4kΩ/50) = 19dB has to be added to this power gain. 1 V 0.5 1 V V 0.5 V Note 5: If a narrow-band match is used in the 2xLO path instead of a 1:2 transformer with 240Ω shunt resistor, 2xLO input power can be reduced to –10dBm, without degrading the phase imbalance. See Figure 11 and Figure 6. Note 6: Differential between IOUT+ and IOUT– (or differential between QOUT+ and QOUT–). Note 7: The gain control voltage VCTRL is set in such a way that the differential output voltage between IOUT+ and IOUT– (or differential between QOUT+ and QOUT–) is 800mVP-P, with the given input power PIF. IF frequencies are 280MHz and 280.1MHz, with f 2xLO = 570MHz. Note 8: The typical parameter is defined as the mean of the absolute values of the data distribution. Note 9: IF frequency is 125MHz, with f 2xLO = 502MHz. 5546f 3 LT5546 U W TYPICAL PERFOR A CE CHARACTERISTICS VCC = 3V, f2×LO = 570MHz, P2×LO = –5dBm (Note 5), f IF = 284MHz, PIF = –30dBm, I and Q outputs 800mVP-P into 4kΩ differential load, TA = 25°C, EN = VCC, STBY = VCC, unless otherwise noted. (Note 3) Gain and Noise Figure Supply Current vs Supply Voltage vs Control Voltage at 3V Supply 28 60 85°C GAIN AND NOISE FIGURE (dB) SUPPLY CURRENT (mA) 50 26 25°C 24 –40°C 22 40 30 20 NF 10 GAIN 0 20 1.75 2.25 2.75 3.25 3.75 4.25 4.75 5.25 SUPPLY VOLTAGE (V) fIF = 284MHz f2xLO = 570MHz –10 0 0.6 0.3 0.9 1.2 5546 G02 Gain and Noise Figure vs Control Voltage at 1.8V Supply Gain Flatness vs Control Voltage at 3V Supply 0.5 GAIN AND NOISE FIGURE (dB) 50 40 30 20 GAIN 0 fIF = 284MHz f2xLO = 570MHz –10 0 0.3 0.6 0.9 1.2 1.5 GAIN AT –40°C NF AT 25°C GAIN AT 25°C NF AT –40°C GAIN AT 85°C NF AT 85°C GAIN DEVIATI0N FROM LINEAR FIT (dB) 60 NF –40°C 0.4 0.3 0.2 85°C 0.1 0 –0.1 25°C –0.2 –0.3 –0.4 –0.5 0 1.8 VCTRL (V) 0.3 0.9 0.6 VCTRL (V) 1.2 1.5 5546 G04 5546 G03 Gain and Noise Figure vs IF Frequency at 3V Supply Gain and Noise Figure vs Control Voltage and VCC 60 60 50 50 GAIN, VCTRL = 1.6V 40 30 20 NF 10 GAIN 0 fIF = 284MHz f2xLO = 570MHz –10 0 0.3 0.6 0.9 1.2 1.5 1.8 VCTRL (V) 5546 G05 GAIN AT 1.8V NF AT 1.8V GAIN AT 3V NF AT 3V GAIN AT 5.25V NF AT 5.25V GAIN AND NOISE FIGURE (dB) GAIN AND NOISE FIGURE (dB) 1.8 1.5 VCTRL (V) 5546 G01 10 GAIN AT 25°C NF AT 25°C GAIN AT –40°C NF AT –40°C GAIN AT 85°C NF AT 85°C NF, VCTRL = 0.2V 40 GAIN, VCTRL = 0.9V 30 NF, VCTRL = 0.9V 20 NF, VCTRL = 1.6V 10 0 GAIN, VCTRL = 0.2V –10 10 100 IF FREQUENCY (MHz) 1000 5546 G06 5546f 4 LT5546 U W TYPICAL PERFOR A CE CHARACTERISTICS VCC = 3V, f2×LO = 570MHz, P2×LO = –5dBm (Note 5), f IF = 284MHz, PIF = –30dBm, I and Q outputs 800mVP-P into 4kΩ differential load, TA = 25°C, EN = VCC, STBY = VCC, unless otherwise noted. (Note 3) Total Harmonic Distortion vs IF Input Power and IF Frequency Total Harmonic Distortion vs IF Input Power at 3V Supply and 800mVP-P Differential Out –25 –25 fIF,1 = 280MHz fIF,2 = 280.1MHz f2xLO = 570MHz –30 –30 –25 800mVP-P DIFFERENTIAL OUT 3V SUPPLY 25°C –45 –40°C –40 –45 –50 85°C –55 –50 –40 –20 –30 IF INPUT POWER EACH TONE (dBm) fIF = 40MHz –60 –60 –10 –55 –50 –40 –20 –30 IF INPUT POWER EACH TONE (dBm) –25 –30 THD (dBc) THD (dBc) –45 5.25V –55 –40 –20 –30 IF INPUT POWER EACH TONE (dBm) –2 –40°C –45 25°C LPF Frequency Response vs Baseband Frequency and Supply Voltage 0 85°C –4 –5 25°C –6 –7 –8 –60 –9 –10 –35 –30 –25 IF INPUT POWER EACH TONE (dBm) 5546 G10 –40°C –3 –55 –65 –40 –10 VCC = 3V –1 –40 –50 –50 –20 85°C 5 10 15 20 25 30 35 40 45 50 55 BASEBAND FREQUENCY (MHz) 0 5546 G12 5546 G11 IF Detector Output Voltage vs IF Input CW Power at 3V Supply 1.4 TA = 25°C –10 5546 G09 0 fIF,1 = 280MHz fIF,2 = 280.1MHz f2xLO = 570MHz VCC = 3V –35 3V –50 –40 –20 –30 IF INPUT POWER EACH TONE (dBm) LPF Frequency Response vs Baseband Frequency and Temperature –20 800mVP-P DIFFERENTIAL OUT fIF,1 = 280MHz –30 f IF,2 = 280.1MHz f2xLO = 570MHz –35 –50 –60 –60 –10 5546 G08 –25 –60 –60 –45 Total Harmonic Distortion vs IF Input Power at 500mVP-P Differential Out Total Harmonic Distortion vs IF Input Power and Supply Voltage 1.8V –40 fIF = 500MHz 5546 G07 –40 85°C –40°C –50 –55 –60 –60 25°C fIF = 280MHz MAGNITUDE (dB) –50 –35 THD (dBc) THD (dBc) –40 fIF,1 = 280MHz fIF,2 = 280.1MHz f2xLO = 570MHz –30 –35 –35 THD (dBc) Total Harmonic Distortion vs IF Input Power at 1.8V Supply and 800mVP-P Differential Out IF Detector Output Voltage vs IF Input CW Power at 1.8V Supply 1.4 fIF = 280MHz fIF = 280MHz –1 –4 –5 3V –6 –7 –8 0 1.0 85°C 0.8 25°C 0.6 0.4 5.25V –9 5 10 15 20 25 30 35 40 45 50 55 BASEBAND FREQUENCY (MHz) 5546 G13 IF DET OUTPUT (V) IF DET OUTPUT (V) MAGNITUDE (dB) 1.8V –3 –10 1.2 1.2 –2 –30 –20 –10 0 IF INPUT CW POWER (dBm) 85°C 0.8 10 5546 G14 25°C 0.6 0.4 –40°C 0.2 –40 1.0 –40°C 0.2 –40 –30 –20 –10 0 IF INPUT CW POWER (dBm) 10 5546 G15 5546f 5 LT5546 U W TYPICAL PERFOR A CE CHARACTERISTICS VCC = 3V, f2×LO = 570MHz, P2×LO = –5dBm (Note 5), f IF = 284MHz, PIF = –30dBm, I and Q outputs 800mVP-P into 4kΩ differential load, TA = 25°C, EN = VCC, STBY = VCC, unless otherwise noted. (Note 3) IF Detector Output Voltage vs IF Input CW Power and Supply Voltage 1.4 fIF = 280MHz IF DET OUTPUT (V) IF DET OUTPUT (V) 5.25V 1.0 3V 1.8V 0.8 0.6 94 fIF = 280MHz 93 fIF = 40MHz 0.8 0.6 0.4 0.2 –40 0.2 –40 10 fIF = 500MHz 1.0 0.4 –30 –20 –10 0 IF INPUT CW POWER (dBm) 95 VCC = 3V 1.2 1.2 Phase Relation Between I and Q Outputs vs LO Input Power PHASE (DEG) 1.4 IF Detector Output Voltage vs IF Input CW Power and IF Frequency fIF = 284MHz, 25°C fIF = 284MHz, –40°C fIF = 284MHz, 85°C fIF = 40MHz, 25°C fIF = 500MHz, 25°C 92 91 90 89 –30 –20 –10 0 IF INPUT CW POWER (dBm) 5546 G16 10 5546 G17 VCC = 3V 88 –20 –15 0 –5 –10 LO INPUT POWER (dBm) 5 10 5546 G18 U U U PI FU CTIO S GND (Pins 1, 4 and 17): Ground. Pins 1 and 4 are connected to each other internally. The exposed pad (Pin 17) is not connected internally to Pins 1 and 4. For chip functionality, the exposed pad and either Pin 1 or Pin 4 must be connected to ground. For best RF performance, Pin 1, Pin␣ 4 and the exposed pad should be connected to RF ground. IF+, IF– (Pins 2, 3): Differential Inputs for the IF Signal. Each pin must be DC grounded through an external inductor or RF transformer with central ground tap. This path should have a DC resistance lower than 2Ω to ground. EN (Pin 9): Enable Input. When the enable pin voltage is higher than 1V, the IC is completely turned on. When the input voltage is less than 0.5V, the IC is turned off, except the part of the circuit associated with standby mode. 2xLO–, 2xLO+ (Pins 10, 11): Differential Inputs for the 2xLO Input. The 2xLO input frequency must be twice that of the IF frequency. The internal bias voltage is VCC – 0.4V. STBY (Pin 12): Standby Input. When the STBY pin is higher than 1V, the standby mode circuit is turned on to prebias the I/Q buffers. When the STBY pin is less than 0.5V, the standby mode circuit is turned off. VCC (Pins 5 and 8): Power Supply. These pins should be decoupled to ground using 1000pF and 0.1µF capacitors. QOUT–, QOUT+ (Pins 13, 14): Differential Baseband Outputs of the Q Channel. Internally biased at VCC – 1.19V. VCTRL (Pin 6): VGA Gain Control Input. This pin controls the IF gain and its typical input voltage range is 0.2V to 1.7V. It is internally biased via a 25k resistor to 0.2V, setting a low gain if the VCTRL pin is left floating. IOUT–, IOUT+ (Pins 15, 16): Differential Baseband Outputs of the I Channel. Internally biased at VCC – 1.19V. IF DET (Pin 7): IF Detector Output. For strong IF input signals, the DC level at this pin is a function of the IF input signal level. 5546f 6 LT5546 W BLOCK DIAGRA VCC VCC 5 IF + 2 VGA 8 I-MIXER IF – 3 LPF CLIPPER 16 IOUT+ 15 IOUT– 90° 7 IF DET VCTRL 6 2×LO + DETECTOR Q-MIXER LPF 11 ÷2 0° CLIPPER 2×LO – 10 9 1 EN 4 + 14 QOUT 17 12 STBY – 13 QOUT 5546 BD U W U U APPLICATIO S I FOR ATIO The LT5546 consists of a variable gain amplifier (VGA), I/Q demodulator, quadrature LO generator, lowpass filters (LPFs), clipping amplifiers (clippers) and bias circuitry. The IF signal is fed to the inputs of the VGA. The VGA gain is typically set by an external signal in such a way that the amplified IF signal delivered to the I/Q mixers is constant. The IF signal is then converted into I/Q baseband signals using the I/Q down-converting mixers. The quadrature LO signals that drive the mixers are internally generated from the on-chip divide-by-two circuit. The I/Q signals are passed through first-order low-pass filters and subsequently a pair of hard-clipping amplifiers (clippers). After externally setting the required gain, these amplifiers should not clip. However, in the event of overload, they reduce the settling time of any (optional) external AC coupling capacitors by preventing asymmetrical charging and discharging effects. The I/Q baseband outputs are buffered by output drivers. VGA and Input Matching The VGA has a nominal 60dB gain control range with a frequency range of 40MHz to 500MHz. The inputs of the VGA must have a DC return to ground. This can be done using a transformer with a central tap (on the secondary) or an LC matching circuit with a matched impedance at the frequency of interest and near zero impedance at DC. The differential AC input impedance of the LT5546 is about 200Ω, thus a 1:4 (impedance ratio) RF transformer with center tap can be used. In Figure 6, the evaluation board schematic is shown using a 1:4 transformer. The measured input sensitivity of this board is about –80.5dBm for a 10dB signal-to-noise ratio. In the case of an L-C matching circuit, the circuit of Figure 1 can be used. In Table 1 the matching network component values are given for a range of IF frequencies. The matching circuit of Figure 1 approaches 180° phase shift between IF+ and IF– in a broad range around its center frequency. However, some amplitude mismatch occurs if the circuit is not tuned to the center frequency. This leads to reduced circuit linearity performance, because one of the inputs carries a higher signal compared to the perfectly balanced case. A 10% frequency shift from the center frequency results in about a 2dB gain difference between the IF+ and IF– inputs. This results in a 1.5dB higher IM3 contribution from the input stage which leads to a 0.75dB drop in IIP3. Moreover, the IIP2 of the circuit is also reduced which can lead to a higher second order harmonic contribution. The circuit can be driven single ended, but this is not recommended because it leads to a 3dB drop in gain and a considerable increase in IM5 and IM7 components. The single-ended noise figure increases by 4dB if one IF input is directly grounded and increases by 1.5dB if one IF input is grounded via a 1µH inductor. An IF input cannot be left open or connected via a resistor to ground because this will disturb the internal biasing, reducing the gain, noise and linearity performance. For optimal performance, it is important to keep the DC impedance to ground of both IF inputs lower than 2Ω. In the matching network of Figure 1, inductor L3 is used for supplying the DC bias current to the IF+ input. 5546f 7 LT5546 U U W U APPLICATIO S I FOR ATIO C3 56pF L1 56nH IF INPUT TO IF IF INPUT + TO IF + C1 10pF TO IF – TO IF – L3 120nH C1 5.6pF L2 56nH L1 15nH C2 5.6pF L2 15nH VBIAS 75Ω 1mA 1mA IF + 75Ω IF – 5546 F02 5546 F01 (2a) (2b) Figure 1. Example L-C IF Input Matching Network at 280MHz Figure 2a. Simplified IF Input Matching Network at 280MHz and Figure 2b. Simplified Circuit Schematic of the IF Inputs Table 1. The Component Values of Matching Network L1, L2, L3, C1, C2 and C3. degrees, depending on the quality factor of the network. This will result in a reduction in the gain. The higher the chosen quality factor, the closer the phase difference will approach 180 degrees. However, a higher quality factor will reduce bandwidth and create more loss in the matching network. For minimum board space, 0402 components are used. The measured noise figure for maximum gain with this matching network is about 9.4dB, and the maximum gain is about 55dB. Assuming 0402 inductors with Q = 35, the insertion loss of this network is about 2.5dB. The tolerance for the components in Figure 2a can be 10% for a return loss higher than 10dB and a gain reduction due to mismatch less than 0.5dB. The measured input sensitivity for this matching network (see also Figure␣ 11) is about –78.3dBm for a 10dB signal-to-noise ratio. fIF(MHz) L1, L2(nH) C1, C2(pF) L3(nH) C3(pF) 50 340 34 1800 820 100 159 15.9 470 220 150 106 10.6 470 220 200 80 8.0 470 220 250 64 6.4 120 56 300 53 5.3 120 56 350 45 4.5 120 56 400 40 4.0 120 56 450 35 3.5 120 56 500 32 3.2 120 56 To keep the DC resistance of L3 below 2Ω, 120nH is used. This disturbs the matching network slightly by causing the frequency where the S11 is minimal to be lower than the frequency where the amplitudes of IF+ and IF– are equal. To compensate for this, the value of coupling capacitor C3 is lowered and will contribute some correcting reactance. For low frequencies, it might not be possible to find any practical inductor value for L3 with DC resistance smaller than 2Ω. In that case it is recommended to use a transformer with a center tap. The tolerance for the components in Figure 1 can be 10% for a return loss higher than 16dB and a gain reduction due to mismatch less than 0.3dB. It is possible to simplify the input matching circuit and compromise the performance. In Figure 2a, the simplified matching network is given. This matching network can deliver equal amplitudes to the IF + and IF – inputs for a narrow frequency region, but the phase difference between the inputs will not be exactly 180 degrees. In practice, the phase shift will be around 145 The gain of the VGA is set by the voltage at the VCTRL pin. For high gain settings, both the noise figure and the input IP3 will be low. From a noise figure point of view, it is advantageous to work as closely as possible to the maximum gain point. However, if the voltage at the VCTRL pin is increased beyond the maximum gain point (where additional increase in control voltage does not give an increase in gain), the response time of the gain control circuit is increased. If control speed is crucial, a few dB of gain margin should be allowed from the highest gain point to be sure that at all temperatures, the maximum gain setting is not crossed. At low gain settings, the noise figure and the input IP3 will be high. Optionally, the control voltage VCTRL can be set lower than 0.2V. The normal range is from VCTRL = 0.2V to 1.7V, which results in a nominal gain range from 1.6dB to 56.8dB. The linear-indB gain relation with the VCTRL voltage still holds for control voltages as low as –0.35V. This results in an 5546f 8 LT5546 U W U U APPLICATIO S I FOR ATIO extended gain control range of –23dB to 57dB. The VCTRL pin is a very sensitive input because of its high input impedance and therefore should be well shielded. Signal pickup on the VCTRL pin can lead to spurs and increased noise floor in the I/Q baseband outputs. It can degrade the linearity performance and it can cause asymmetry in the two-tone test. If control speed is not important, 1µF bypass capacitors are recommended between VCTRL and ground. VCC VCC + 400mV – 2xLO + 8k 8k 2xLO – IF DET 1k 3.8k 5546 F03 A fast responding peak detector is connected to the VGA input, sensitive to signal levels above the signal levels where the VGA is operating in the linear range. It is active from –22dBm up to 5dBm IF input signal levels. The DC output voltage of this detector (IF DET) can be used by the baseband controller to quickly determine the presence of a strong input level at the desired channel, and adjust gain accordingly. Figure 3a shows the simplified circuit schematic of the IF DET output. (3b) (3a) Figure 3a. Simplified Circuit Schematic of the IF DET Output and Figure 3b. The 2xLO Inputs 3.3pF 2xLO INPUT 100pF 2xLO INPUT TO 2xLO+ 39nH 2xLO INPUT 1:4 TO 2xLO– TO 2xLO+ 56Ω TO 2xLO+ TO 2xLO– 240Ω 100pF 3.3pF TO 2xLO– I/Q Demodulators The quadrature demodulators are double balanced mixers, down-converting the amplified IF signal from the VGA into I/Q baseband signals. The quadrature LO signals are generated internally from a double frequency external CW signal. The nominal output voltage of the differential I/Q baseband signals should be set to 0.8VP-P or lower, depending on the linearity requirements. The magnitudes of I and Q are well matched and their phases are 90° apart. Quadrature LO Generator The quadrature LO generator consists of a divide-by-two circuit and LO buffers. An input signal (2xLO) with twice the desired IF signal frequency is used as the clock for the divide-by-two circuit, producing the quadrature LO signals for the demodulators. The outputs are buffered and then drive the down-converting mixers. With a fully differential approach, the quadrature LO signals are well matched. Second harmonic content (or higher order even harmonics) in the external 2xLO signal can degrade the 90° phase shift between I and Q. Therefore, such content should be minimized. In disable or standby mode, the divide-by-two stage is powered down. After enabling the circuit, the phase relation between the IF signal and the baseband (I or Q) signals can be either 0° or 180°, since the circuit cannot distinguish between the two subsequent identical sinusoi- 5546 F04 (4a) (4b) (4c) Figure 4. 2xLO Input Matching Networks for 4a) Narrow Band Tuned to 570MHz, 4b) Wide Band, 4c) Single-Ended Wide Band dal waveforms of the 2xLO input signal. The phase relation between I and Q is always 90°, i.e. I always leads Q by 90°. Figure 3b shows the simplified circuit schematic of the 2xLO inputs. Depending on the application, different 2xLO input matching networks can be chosen. In Figure 4, three examples are given. The first network provides the best 2xLO input sensitivity because it can boost the 2xLO differential input signal using a narrow-band resonant approach. The second network gives a wide-band match, but the 2xLO input sensitivity is about 2dB lower. The third network gives a simple and less expensive wide-band match, but 2xLO input sensitivity drops by about 9dB. The IF input sensitivity doesn’t change significantly using any of the three 2xLO matching networks. Baseband Circuit The baseband circuit consists of I/Q low-pass filters, I/Q hard limiters (clippers) and I/Q output buffers. The hard limiters operate as linear amplifiers normally. However, if a high level input temporarily overloads a linear amplifier, then the circuit will limit symmetrically, which will help to prevent the output buffer from overloading. This speeds 5546f 9 LT5546 U W U U APPLICATIO S I FOR ATIO up recovery from an overload event, which can occur during the gain settling. The clipping level is approximately constant over temperature. The first order integrated lowpass filters are used for noise filtering of the down-converted baseband signals for both the I channel and the Q channel. These filters are well matched in gain response. The –3dB corner frequency is typically 17MHz. The I/Q outputs can drive 2kΩ in parallel with a maximum capacitive loading of 10pF at 5MHz, from all four pins to ground. The outputs are internally biased at VCC – 1.19V. Figure 5 shows the simplified output circuit schematic of the I channel or Q channel. and standby mode, the maximum discharging current is about 300µA, and the maximum charging current is more than 4mA. In Figure 5 the simplified circuit schematic of the STBY (or EN) input is shown. Table 2. The Logic of Different Operating Modes EN STBY Comments Low Low Shutdown Mode Low High Standby Mode High Low or High Normal Operation Mode VCC The I/Q baseband outputs can be DC-coupled to the inputs of a baseband chip. For AC-coupled applications with large capacitors, the STBY pin can be used to pre-bias the outputs to nominal VCC – 1.19V at much reduced current. This mode draws only 3.6mA supply current. When the EN pin is then driven high (>1V), the chip is quickly switched to normal operating mode, avoiding the introduction of large charging time constants. Table 2 shows the logic of the EN pin and STBY pin. In both normal operating mode OPTIONAL VCC IOUT+ (OR QOUT+) IOUT– (OR QOUT–) I CHANNEL (OR Q CHANNEL): DIFFERENTIAL SIGNALS FROM LPF 300µA 300µA 5546 F05 Figure 5. Simplified Circuit Schematic of I Channel (or Q Channel) Outputs and STBY (or EN) Input IOUT+ IOUT– QOUT+ QOUT– VCC3 C37 0.1µF J1 22k STBY (OR EN) R47 49.9Ω C31 1µF 7 IOUT + U3 LT1818CS 6 – 4 R48 3.09k C35 4.7µF R50 2k C1 5.6pF R46 3.09k R49 2k R39 3.09k 3 C2 5.6pF 2 + C32 1pF – C29 1pF 16 15 14 C30 1µF 7 U2 LT1818CS R42 2k C28 0.1µF C33 0.1µF 5V C38 0.1µF R43 2k C27 0.1µF R41 1k C34 R45 0.1µF 1k 3 2 C36 4.7µF 6 R44 49.9Ω J2 QOUT 4 R40 3.09k 13 IOUT+ IOUT– QOUT+ QOUT– J3 IFIN C43 22nF T1, 1:4,TR-R JTX-4-10T MINI-CIRCUITS 1 6 1 2 3 4 GND STBY IF + 2XLO+ U1 LT5546 IF – T2, 1:4, TR-R C45 22nF JTX-4-10T MINI-CIRCUITS 12 11 EN VCC2 2XLO R52 240Ω 10 2XLO – GND R35 20k J4 6 9 1 R36 20k IF VCC VCTRL DET VCC 5 6 7 8 17 GND 1 = EN 2 = STBY VCC1 C22 1µF C15 1nF C16 1nF VCTRL R51 100Ω C25 1.5pF SW1 OVERLOAD C26 NOTE: OUTPUT BUFFERS U2 AND U3 WITH ASSOCIATED 1.8pF COMPONENTS ARE INCLUDED FOR EVALUATION ONLY. DEMO BOARD: DC696A C43, C45, C22, R51, C25, C26 AND C39 ARE OPTIONAL C39 1µF 5546 F04 Figure 6. Evaluation Circuit Schematic with I/Q Output Buffers 5546f 10 LT5546 U W U U APPLICATIO S I FOR ATIO Evaluation Board The evaluation circuit schematic is drawn in Figure 6. The components associated with buffers U2 and U3 are included to drive a 50Ω load for evaluation purposes only. There is a unity voltage gain relationship for AC signals between the evaluation board outputs (I and Q) and the IOUT+, IOUT– or QOUT+ and QOUT– outputs of the LT5546 when the evaluation board outputs are terminated in 50Ω. Figure 7. Component Side Silkscreen of Evaluation Board Figure 8. Component Side Layout of Evaluation Board Figure 9. Bottom Side Silkscreen of Evaluation Board Figure 10. Bottom Side Layout of Evaluation Board 15nH 1.8V RX INPUT: 2.4GHz TO 2.5GHz 1µF 10pF 280MHz IF SAW BP FILTER VGA 1ST LO, 2.12GHz TO 2.22GHz MAIN SYNTHESIZER AUX SYNTHESIZER VCC 5, 8 2 RX FRONT END 15nH 1nF I-MIXER LPF BASEBAND PROCESSOR HARD CLIPPER 3 16 15 I-OUTPUTS 7 IF DET 6 VCTRL 14 13 Q-OUTPUTS 0° Q-MIXER 2ND LO, 560MHz –10dBm 90° 11 3.3pF 39nH LPF A/D D/A A/D HARD CLIPPER f/2 12 10 LT5546 3.3pF A/D 9 STBY EN 1,4,17 5546 F11 Figure 11. 2.4GHz to 2.5GHz Receiver Application (RX IF = 280MHz) 5546f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 11 LT5546 U PACKAGE DESCRIPTIO UF Package 16-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1692) BOTTOM VIEW—EXPOSED PAD RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 ± 0.10 (4 SIDES) 0.72 ±0.05 0.75 ± 0.05 R = 0.115 TYP 0.55 ± 0.20 15 16 PIN 1 TOP MARK 1 4.35 ± 0.05 2.15 ± 0.05 2.90 ± 0.05 (4 SIDES) 2 2.15 ± 0.10 (4-SIDES) PACKAGE OUTLINE (UF) QFN 0802 0.30 ± 0.05 0.200 REF 0.30 ±0.05 0.65 BCS NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGC) 2. ALL DIMENSIONS ARE IN MILLIMETERS 0.00 – 0.05 0.65 BSC 3. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 4. EXPOSED PAD SHALL BE SOLDER PLATED RELATED PARTS PART NUMBER Infrastructure LT5511 LT5512 LT5515 DESCRIPTION COMMENTS High Signal Level Upconverting Mixer High Signal Level Downconverting Mixer 1.5GHz to 2.5GHz Direct-Conversion Quadrature Demodulator LT5516 800MHz to 1.5GHz Direct-Conversion Quadrature Demodulator LT5522 600MHz to 2.7GHz High Signal Level Downconverting Mixer RF Power Detectors LT5504 800MHz to 2.7GHz RF Measuring Receiver LTC5505 RF Power Detectors with >40dB Dynamic Range LTC5507 100kHz to 1000MHz RF Power Detector LTC5508 0.3GHz to 7GHz RF Power Detector LTC5509 300MHz to 3GHz RF Power Detector LTC5532 300MHz to 7GHz Precision RF Power Detector RF Receiver Building Blocks LT5500 1.8GHz to 2.7GHz Receiver Front End LT5502 400MHz Quadrature IF Demodulator with RSSI LT5503 1.2GHz to 2.7GHz Direct IQ Modulator and Mixer LT5506 40MHz to 500MHz Quadrature IF Demodulator with VGA RF Output to 3GHz, 17dBm IIP3, Integrated LO Buffer DC-3GHz, 20dBm IIP3, Integrated LO Buffer 20dBm IIP3, NF =16.8dB, Integrated LO Quadrature Generator 4V to 5.25V Supply, 21.5dBm IIP3, NF = 12.8dB, Integrated LO Quadrature Generator 4.5V to 5.25V Supply, 25dBm IIP3 at 900MHz, NF = 12.5dB, 50Ω Single-Ended RF and LO Ports 2.7V to 5.25V Supply, 80dB Dynamic Range, Temperature Compensated 2.7V to 6V Supply, 300MHz to 3.5GHz, Temperature Compensated 2.7V to 6V Supply, 48dB Dynamic Range, Temperature Compensated 2.7V to 6V Supply, 44dB Dynamic Range, Temperature Compensated –30dBm to 6dBm, 600µA Supply Current, Temperature Compensated Precision VOUT Offset Control, Adjustable Gain and Offset 1.8V to 5.25V Supply, Dual-Gain LNA, Mixer 1.8V to 5.25V Supply, 70MHz to 400MHz IF, 84dB Limiting Gain, 90dB RSSI Range 1.8V to 5.25V Supply, Four Step RF Power Control, 120MHz Modulation Bandwidth 1.8V to 5.25V, I/Q Baseband Bandwidth 8.8MHz, –40dB to 57dB Linear Power Gain 5546f 12 Linear Technology Corporation LT/TP 1003 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2003