IF Digitally Controlled Variable-Gain Amplifier

_______________________________________________________________________________________

7

Detailed Description

The MAX2027 is a high-performance, digitally con-

trolled variable-gain amplifier for use in applications

from 50MHz to 400MHz.

The MAX2027 incorporates a digital attenuator with a

23dB selectable attenuation range followed by a fixed-

gain, high-linearity amplifier. The attenuator is digitally

controlled through five logic lines: B0–B4. This on-chip

attenuator provides up to 23dB of attenuation with

±0.05dB state-to-state accuracy. The fixed-gain amplifi-

er utilizes negative feedback to achieve high stability,

gain, linearity, and wide bandwidth.

Applications Information

Input and Output Matching

The MAX2027 incorporates on-chip input and output

matching for operation below 250MHz. Use a DC-block-

ing capacitor value of 1000pF for pins 3, 12, and 18 (see

Figure 1). For operation above 250MHz, external match-

ing improves performance. Table 1 and Table 2 provide

recommended components for device operation.

Digitally Controlled Attenuator

The digital attenuator is controlled through five logic

lines: B0, B1, B2, B3, and B4. Table 3 lists the attenua-

tion settings. The input and output of this attenuator

require external DC-blocking capacitors. This attenua-

tor insertion loss is 2dB when the attenuator is set to

0dB (B0 = B1 = B2 = B3 = B4 = 0).

Pin Description

PIN

NAME

FUNCTION

1, 2, 11

Power Supply. Bypass to GND with capacitors as close to the pin as possible as shown in the typical

application circuit (Figure 1).

3

RF_IN

Signal Input. See the typical application circuit for recommended component values. Requires an

external DC-blocking capacitor.

4, 5, 16, 17,

19, 20, EP

GND

Ground. Use low-inductance layout techniques on PC board. Solder the exposed pad evenly to the

board ground plane.

6–10

B4–B0

Gain-Control Bits. See Table 3 for gain setting.

12

RF_OUT

DC-blocking capacitor (Figure 1).

13

Connect an 825

14

15

Amplifier Input. Requires a DC-coupling capacitor to allow biasing.

18

Attenuator Output. Requires an external DC-blocking capacitor.

COMPONENT

VALUE

SIZE

C1, C3, C4

1000pF

0603

C2, C5

100pF

0603

C6, C7

0.1µF

0603

C10

0.047µF

0603

R1

825

Ω ±1%

0603

R2–R6

47k

Ω

0603

L1

330nH

0805

L2

680nH

1008

Table 1. Suggested Components of

Typical Application Circuit

FREQUENCY

COMPONENT

VALUE

SIZE

L3, L4

11nH

0603

300MHz

C8, C9

6.8pF

0603

L3, L4

8.7nH

0603

400MHz

C8, C9

5pF

0603

Table 2. Suggested Matching

Components