ADL5350ACPZ-R7 Datasheet ADL5350ACPZ-R7, ADL5350-EVALZ | P16-P18

ADL5350

Rev. 0 | Page 16 of 24

Supply voltage = 3 V, RF frequency = 1950 MHz, IF frequency = 190 MHz, RF level = −10 dBm, LO level = 6 dBm, T

= 25°C,

unless otherwise noted.

–

–9

–10

–11

–12

–13

–14

–15

1800 2050202520001975195019251900187518501825

IF FEEDTHROUGH (dBc)

RF FREQUENCY (MHz)

+85°C

+25°C

–40°C

05615-054

Figure 54. IF Feedthrough vs. RF Frequency

–

–10

–12

–16

–18

–14

–9

–11

–13

–17

–15

1610 186018351785 1810176017351710168516601635

IF FEEDTHROUGH (dBc)

LO FREQUENCY (MHz)

05615-055

+25°C

–40°C

+85°C

Figure 55. IF Feedthrough vs. LO Frequency

–14

–12

–10

–8

–6

–4

–2

1560 1610 1660 1710 1760 1810 1860 1910 1960

RF LEAKAGE (dBc)

LO FREQUENCY (MHz)

05615-056

Figure 56. RF Leakage vs. LO Frequency

ADL5350

Rev. 0 | Page 17 of 24

FUNCTIONAL DESCRIPTION

CIRCUIT DESCRIPTION

The ADL5350 is a GaAs pHEMT, single-ended, passive

mixer with an integrated LO buffer amplifier. The device

relies on the varying drain to source channel conductance

of a FET junction to modulate an RF signal. A simplified

schematic is shown in

Figure 57.

GND1 GND2

LOIN

INPU

VPOS

INPUT

OR OUTPUT

OUTPUT

OR INPUT

05615-057

Figure 57. Simplified Schematic

The LO signal is applied to the gate contact of a FET-based

buffer amplifier. The buffer amplifier provides sufficient

gain of the LO signal to drive the resistive switch. Additionally,

feedback circuitry provides the necessary bias to the FET

buffer amplifier and RF/IF ports to achieve optimum

modulation efficiency for common cellular frequencies.

The mixing of RF and LO signals is achieved by switching

the channel conductance from the RF/IF port to ground at

the rate of the LO. The RF signal is passed through an external

band-pass network to help reject image bands and reduce

the broadband noise presented to the mixer. The band-

limited RF signal is presented to the time-varying load of

the RF/IF port, which causes the envelope of the RF signal

to be amplitude modulated at the rate of the LO. A filter

network applied to the IF port is necessary to reject the

RF signal and pass the wanted mixing product. In a down-

conversion application, the IF filter network is designed to

pass the difference frequency and present an open circuit

to the incident RF frequency. Similarly, for an upconversion

application, the filter is designed to pass the sum frequency

and reject the incident RF. As a result, the frequency response

of the mixer is determined by the response characteristics

of the external RF/IF filter networks.

IMPLEMENTATION PROCEDURE

The ADL5350 is a simple single-ended mixer that relies

on off-chip circuitry to achieve effective RF dynamic

performance. The following steps should be followed

to achieve optimum performance (see

Figure 58 for

component designations):

RF/IF GND2 LOIN NC

RF/IF NC VPOS

C2L2

GND1

ADL5350

1234

8765

05615-058

Figure 58. Reference Schematic

1. Table 7 shows the recommended LO bias inductor

values for a variety of LO frequencies. To ensure efficient

commutation of the mixer, the bias inductor needs to

be properly set. For other frequencies within the range

shown, the values can be interpolated. For frequencies

outside this range, see the

Applications Information section.

Table 7. Recommended LO Bias Inductor

Desired LO Frequency (MHz)

Recommended LO Bias

Inductor, L4

(nH)

380 68

750 24

1000 18

1750 3.8

2000 2.1

The bias inductor should have a self-resonant frequency greater than

the intended frequency of operation.

ADL5350

Rev. 0 | Page 18 of 24

2. Tune the LO port input network for optimum return

loss. Typically, a band-pass network is used to pass the

LO signal to the LOIN pin. It is recommended to block

high frequency harmonics of the LO from the mixer

core. LO harmonics cause higher RF frequency images

to be downconverted to the desired IF frequency and

result in sensitivity degradation. If the intended LO

source has poor harmonic distortion and spectral purity,

it may be necessary to employ a higher order band-pass

filter network.

Figure 58 illustrates a simple LC band-

pass filter used to pass the fundamental frequency of the

LO source. Capacitor C3 is a simple dc block, while the

Series Inductor L3, along with the gate-to-source

capacitance of the buffer amplifier, form a low-pass

network. The native gate input of the LO buffer (FET)

alone presents a rather high input impedance. The gate

bias is generated internally using feedback that can result

in a positive return loss at the intended LO frequency.

If a better than −10 dB return loss is desired, it may be

necessary to add a shunt resistor to ground before the

coupling capacitor (C3) to present a lower loading

impedance to the LO source. In doing so, a slightly

greater LO drive level may be required.

3. Design the RF and IF filter networks.

Figure 58 depicts

simple LC tank filter networks for the IF and RF port

interfaces. The RF port LC network is designed to pass

the RF input signal. The series LC tank has a resonant

frequency at 1/(2π√LC). At resonance, the series reactances

are canceled, which presents a series short to the RF

signal. A parallel LC tank is used on the IF port to reject

the RF and LO signals. At resonance, the parallel LC tank

presents an open circuit.

It is necessary to account for the board parasitics, finite

Q, and self-resonant frequencies of the LC components

when designing the RF, IF, and LO filter networks.

Table 8

provides suggested values for initial prototyping.

Table 8. Suggested RF, IF, and LO Filter Networks for Low-Side LO Injection

RF Frequency (MHz) L1 (nH)

C1 (pF) L2 (nH) C2 (pF) L3 (nH) C3 (pF)

450 8.3 10 10 10 10 100

850 6.8 4.7 4.7 5.6 8.2 100

1950 1.7 1.5 1.7 1.2 3.5 100

2400 0.67 1 1.5 0.7 3.0 100

The inductor should have a self-resonant frequency greater than the intended frequency of operation. L1 should be a high Q inductor for optimum NF performance.

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ADL5350ACPZ-R7

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