Data Sheet

ADRF5700

THEORY OF OPERATION

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Rev. 0 | 13 of 16

The ADRF5700 incorporates a 5-bit fixed attenuator array that

offers an attenuation range of 46 dB in 2 dB steps. An integrated

driver provides parallel mode control of the attenuator array.

The ADRF5700 has five digital control inputs, D2 (LSB) to D6

(MSB), to select the desired attenuation state in parallel mode, as

shown in Figure 23. Internally, there are two 16 dB stages, and

these stages can be controlled by the D5 and D6 pins.

POWER SUPPLY

The ADRF5700 requires a positive supply voltage applied to the

VDD pin and a negative supply voltage applied to the VSS pin.

Bypassing capacitors are recommended on the supply lines to filter

high frequency noise.

The power-up sequence is as follows:

1. Connect GND.

2. Power up the VDD and VSS voltages. Power up VSS after VDD

to avoid current transients on VDD during ramp-up.

3. Power up the digital control inputs. The order of the digital

control inputs is not important. However, powering the digital

control inputs before the VDD voltage supply can inadvertently

forward bias and damage the internal ESD structures. To avoid

this damage, use a series 1 kΩ resistor to limit the current

flowing into the control pin.

4. Apply an RF input signal to ATTIN or ATTOUT.

The power-down sequence is the reverse order of the power-up

sequence.

Power-Up State

The ADRF5700 has an internal pull-up resistor (see Figure 6).

The internal pull-up resistor sets the attenuator to the maximum

attenuation state (46 dB) when the VDD and VSS voltages are

applied if D2 to D6 are left floating.

Single-Supply Operation

The ADRF5700 can operate with a single positive supply voltage

applied to the VDD pin and the VSS pin connected to ground.

However, some performance difference can occur in the switching

characteristics and large signal (see the Electrical Specifications

section for further information).

RF INPUT AND OUTPUT

Both RF ports (ATTIN and ATTOUT) are DC-coupled to 0 V. No DC

blocking is required at the RF ports when the RF line potential is

equal to 0 V.

The RF ports are internally matched to 50 Ω. Therefore, external

matching components are not required.

The ADRF5700 supports bidirectional operation with equal power

handling capability. Refer to the RF input power specifications in

Table 1.

Table 8. Truth Table

Digital Control Input1

Attenuation State (dB)

D62

D52

D4

D3

D2

Low

Low

Low

Low

Low

0 (reference)

Low

Low

Low

Low

High

2

Low

Low

Low

High

Low

4

Low

Low

High

Low

Low

8

Low

High

Low

Low

Low

16 (D5)

High

Low

Low

Low

Low

16 (D6)

High

High

High

High

High

46

1 Any combination of the VCTRL input states provides an attenuation equal to the sum of the bits selected.

2 D5 and D6 both correspond to the 16 dB state. D5 has slightly better state accuracy at higher frequencies.

Figure 23. Simplified Circuit Diagram