Linear Technology 1233A Series Manual de usuario

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1233A-X

1.5GHZ TO 3.8GHZ HIGH LINEARITY UPCONVERTING MIXER

LT5579

DESCRIPTION

Demonstration circuit 1233A-x is a high linearity up-

converting mixer featuring the LT5579.

The LT

5579 is a high performance upconverting mixer

IC optimized for output frequencies in the 1.5GHz to

3.8GHz range. It features single-ended LO input and RF

output ports to simplify board layout and to reduce sys-

tem cost.

The LT5579 offers a superior alternative to passive mix-

ers. Unlike passive mixers which have conversion loss

and require high LO drive levels, the LT5579 delivers

conversion gain at significantly lower LO input levels

and is less sensitive to LO power level variations. Only

-1dBm of LO power is needed, and the balanced design

results in low LO signal leakage to the RF output. The

lower LO drive level requirements, combined with the

excellent LO leakage performance, translate into lower

LO signal contamination of the output signal.

The DC1233A-x series of demonstration circuits are

designed for evaluating the LT5579 IC at several com-

mon frequency ranges:

VERSION APPLICATION IF INPUT LO INPUT RF OUTPUT

WiMAX

456MHz

Low

side

3.6GHz

iMAX

456MHz

High

side

2.6GHz

UMTS

240MHz

High

side

2.14GHz

PCS

240MHz

Low

side

1.95GHz

Demonstration circuit 1233A-x can be easily optimized

for operations at other frequencies. Refer to the “Appli-

cation Note” section and the LT5579 data sheet for de-

tails.

Design files for this circuit board are available. Call

the LTC factory.

, LT, LTC, and LTM are registered trademarks of Linear Technology Corp.

All other trademarks are the property of their respective owners.

Table 1. Typical Demo Circuit Performance Summary (T

= 25°C, V

= 3.3V, P

= -5dBm (-5dBm/tone for 2-tone tests,

∆

∆∆

∆

f = 1MHz),

= -1dBm, unless otherwise noted. Low side LO for 1950MHz and 3600MHz. High side LO for 2140MHz and 2600MHz.)

PARAMETER CONDITIONS TYPICAL PERFORMANCE

Supply Voltage

3.3V

Supply Current

226mA

LO Input Frequency Range

1.1GHz to 4GHz

LO Input Power

5 to +2dBm

1233A

WiMAX 3.6GHz

WiMAX 2.6GHz

UMTS

PCS

IF Input Frequency Range

12dB Return Loss, LO applied

330 to 505MHz

174 to 263MHz

RF Output Frequency Range

10dB Return Loss,

LO applied

3170 to 4100MHz

2260 to 2780MHz

2035 to 2285MHz

1840 to 2020MHz

Conversion Gain

0.5dB

1.3dB

2.6dB

1.9dB

Conversion Gain vs. Temperature

40°C to 85°C

0.027dB/°C

0.020dB/°C

Output 3rd Order Intercept

23.2dBm

26.2dBm

27.3dBm

28dBm

Output 2nd Order Intercept

54dBm

45dBm

42dBm

40dBm

Single Sideband Noise Figure

12dB

9.9dB

Output Noise Floor

OUT

5dBm

155.5dBm/Hz

157.5dBm/Hz

158.1dBm/Hz

Output 1dB Compression

10.7dBm

13.7dBm

.9dBm

13.6dBm

IF to LO Isolation

73dB

74dB

81dB

80dB

LO to IF Leakage

22dBm

26dBm

28dBm

25dBm

LO to RF Leakage

35dBm

36dBm

35dBm

34dBm

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1233A-X

1.5GHZ TO 3.8GHZ HIGH LINEARITY UPCONVERTING MIXER

APPLICATION NOTE

ABSOLUTE MAXIMUM RATINGS

Supply Voltage......................................................3.6V

LO Input Power.............................................. +10dBm

LO Input DC Voltage .................... -0.3V to V

+ 0.3V

RF Output DC Current........................................ 60mA

IF Input Power (Differential).......................... +13dBm

, IF

DC Currents ........................................... 60mA

JMAX

.................................................................150°C

Operating Temperature Range.............. -40°C to 85°C

Storage Temperature Range............... -65°C to 150°C

IF INPUT INTERFACE

The standard demonstration circuit 1233A-x can be re-

configured for other IF input frequencies. The details of

the matching circuit are omitted in this guide, since the

LT5579 datasheet presents in depth explanations and

the IC’s IF input differential impedance. Matching com-

ponent values for several common IF input frequencies

are listed in Table 2. Refer to the demonstration circuit

schematic in Figure 3.

Table 2. IF Input Component Values

IF Freq.

(MHz)

C1,C2

(pF)

C9 (1)

(pF)

TL1,TL2

(3)

L1,L2

(nH)

R1,R2

(

Ω

ΩΩ

Ω

)

70 1000 120 (2) 4.7nH 100 9.1

140 1000 120 (2) Z

=70

Ω

100 9.1

240 82 33 (2) Z

=70

Ω

40 11

450 33 33 (2) Z

=70

Ω

40 11

NOTE:

Center of C9 is 3mm from the edge of the IC package

for all cases.

C3 is a small-valued capacitor used to improve the

LO-RF leakage in some applications, and it has little

effect on impedance matching. C3’s value and loca-

tion depend on LO and RF frequencies and are de-

termined experimentally. In certain instances, two

common-mode capacitors to ground instead of one

single differential capacitor may provide better leak-

age suppression.

The 70

Ω

microstrip transmission line TL1 and TL2

provide inductances required for matching. At lower

frequencies, external inductors are necessary.

R1 and R2 set the DC current in the mixer core to the

optimum level of 50mA per side. Their values should

be well matched for best LO leakage performance.

0.1% tolerance is recommended.

L1 and L2 reduce the loading effect of R1 and R2.

Their self-resonant frequency should be at least sev-

eral times the IF frequency. High quality wire-wound

type inductors are recommended. The DC resis-

tances of L1 and L2 need to be accounted for in the

selection of R1 and R2.

LO INPUT INTERFACE

The LT5579’s LO input port is internally matched from

1.1GHz to 4GHz, with a minimum return loss across

this range of about 9dB at 2.3GHz. External matching

should be used for lower LO frequencies for best per-

formance. Refer to the LT5579 datasheet for more in-

formation and impedance data.

RF OUTPUT INTERFACE

The LT5579 utilizes an internal RF transformer to step

down the mixer core output impedance to simply RF

output matching. Matching component values for sev-

eral common RF output frequencies are listed in Table

3. High quality precision microwave capacitors, such

as the AVX Accu-p series, should be used for C8 to

minimize parasitics.

Table 3. RF Output Component Values

RF Frequency (MHz) C8 (pF) L3 (nH)

1650 1.5 6.8

1750 1.2 6.8

1950 1 4.7

2140 0.45 3.9

2600 - 1.0

3600 0.7 0

Ω

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1233A-X

1.5GHZ TO 3.8GHZ HIGH LINEARITY UPCONVERTING MIXER

TEST EQUIPMENT AND SETUP

The LT5579 is a high linearity upconverting mixer IC.

Accuracy of its performance measurement is highly

dependent on equipment setup and measurement tech-

nique. The following precautions are recommended:

Use high performance signal generators with low

harmonic output. Otherwise, utilize low-pass fil-

ters at the signal generator outputs to suppress

higher-order harmonics.

Turn off the signal generators’ output automatic-

level-control (ALC). This prevents conflict in

power-level control between the two sources,

which can introduce intermodulation products.

High quality combiners that provide broadband

50Ω

ΩΩ

Ωtermination on all ports and have good port-

to-port isolation should be used. Attenuators on

the outputs of the signal generators are recom-

mended to further improve source isolation to

prevent the sources from modulating each other

and generating intermodulation products.

Beware of the signal generators’, and if used, source

amplifiers’ 1dB compression point. When driven

close to their 1dB compression point, the sources

and amplifiers may introduce additional distortions.

The level of intermodulation products from the input

sources needs to be much lower than the products

expected to be generated by the DUT. In general, IM

products measured at the input connector to the DUT

should be 25dB or more below the expected level at

the DUT output.

If possible, use small attenuator pads with good

VSWR on the demonstration circuit’s input and

output ports to improve source and load match to

reduce reflections, which may degrade measure-

ment accuracy.

Use narrow resolution bandwidth (RBW) and en-

gage video averaging on the spectrum analyzer to

lower the displayed average noise level (DANL) in

order to improve sensitivity and to increase dy-

namic range. The trade off is increased sweep

time.

Spectrum analyzers can produce significant internal

distortion products if they are overdriven. Generally,

spectrum analyzers are designed to operate at their

best with about –30dBm to -40dBm at their input fil-

ter or preselector.

Sufficient spectrum analyzer in-

put attenuation should be used to avoid saturating

the instrument, but too much attenuation reduces

sensitivity and dynamic range.

Before performing measurements on the demo

circuit, the system performance should be evalu-

ated to ensure that: 1) clean input signal can be

produced, 2) the spectrum analyzer’s internal dis-

tortion is minimized, 3) the spectrum analyzer has

enough dynamic range and sensitivity, and 4) the

system is accurately calibrated for power and fre-

quency.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1233A-X

1.5GHZ TO 3.8GHZ HIGH LINEARITY UPCONVERTING MIXER

QUICK START PROCEDURE

Demonstration circuit 1233A-x is easy to set up to

evaluate the performance of the LT5579. Refer to

Figure 1 and Figure 2 for proper measurement equip-

ment connections and follow the procedure below:

NOTE:

Care should be taken to never exceed absolute

maximum input ratings.

RETURN LOSS MEASUREMENTS

Configure the Network Analyzer for return loss

measurement, set appropriate frequency range,

and set the test signal to –5dBm.

Calibrate the Network Analyzer.

Connect all test equipment as shown in

Figure 1

Apply 3.3V DC supply power, and verify that the

current consumption is approximately 226mA in

the presence of LO signal. The supply voltage

should be confirmed at the demo board V

and

GND terminals to account for ohmic losses due to

the high current.

With the LO signal applied, and the unused demo

board port terminated in 50Ω, measure return

loss of the IF input and RF output ports.

Set the test signal to –1dBm, and re-calibrate the

Network Analyzer.

Terminate the IF input and RF output ports in 50Ω.

Measure return loss of the LO input port.

RF PERFORMANCE MEASUREMENTS

Connect all test equipment as shown in Figure 2

Set the LO source (Signal Generator 1) to provide

a -1dBm, CW signal to the demo board LO input

port at appropriate LO frequency.

Set the IF sources (Signal Generators 2 and 3) to

provide two -5dBm CW signals, 1MHz apart, to

the demo board IF input port at the appropriate IF

frequency.

Measure the resulting RF output on the Spectrum

Analyzer:

The wanted two-tone RF output signals are at:

OUT(1,2)

= f

+ f

IF(1,2)

for low-side LO, and

OUT(1,2)

= f

– f

IF(1,2)

for high-side LO

The 2nd order intermodulation product which is

closest to the wanted RF signals is used to cal-

culate the Output 2nd Order Intercept:

IM2

= f

+ (f

IF1

+ f

IF2

) for low-side LO, and

IM2

= f

- (f

IF1

+ f

IF2

) for high-side LO

Similarly, use the 3rd order intermodulation

products which are closest to the wanted RF

signals to calculate the Output 3rd Order Inter-

cept:

IM3,1

= f

+ f

IF1

- ∆

, and

IM3,2

= f

+ f

IF2

+ ∆

for low-side LO, and

IM3,1

= f

- f

IF1

+ ∆

, and

IM3,2

= f

- f

IF2

- ∆

for high-side LO

Where

∆

= f

IF2

– f

IF1

Calculate Output 2nd and 3rd Order Intercepts:

OIP2 = 2•P

OUT

– P

IM2

OIP3 = (3•P

OUT

– P

IM3

) / 2

Where P

OUT

is the lowest power level of the two

wanted output signals at either f

OUT1

or f

OUT2

, P

IM2

the 2nd order intermodulation product at f

IM2

, and

IM3

is the largest 3rd order intermodulation product

at either f

IM3,1

or f

IM3,2

. All units are in dBm.

Alternatively, the output intercept can be calculated

using the power difference between the desired out-

put signal and the intermodulation products:

OIP2 =

∆

IM2

+ P

OUT

OIP3 = (∆

IM3

)/2 + P

OUT

Where

∆

IM(2,3)

= P

OUT

– P

IM(2,3)

Turn off one of the IF signal generators, and measure

Conversion Gain, IF to LO isolation, LO to IF and LO

to RF leakages, and Input 1dB compression point.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1233A-X

1.5GHZ TO 3.8GHZ HIGH LINEARITY UPCONVERTING MIXER

Figure 1. Proper Equipment Setup for Return Loss Measurements

Figure 2. Proper Equipment Setup for RF Performance Measurements

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1233A-X

1.5GHZ TO 3.8GHZ HIGH LINEARITY UPCONVERTING MIXER

Figure 3. Demonstration Circuit Schematic

Mouser Electronics

Authorized Distributor

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