Application information

RHF1401

18/29

Single-ended signal with transformer

Using an RF transformer is an efficient method of achieving high performance.

Figure 21 shows the schematic view. The input signal is fed to the primary of the

transformer, while the secondary drives both ADC inputs.

Figure 21.

Differential input configuration with transformer

The internal common mode voltage of the ADC (INCM) is connected to the center-tap of the

secondary of the transformer in order to bias the input signal around this common voltage,

internally set to 0.46 V. The INCM is decoupled to maintain a low noise level on this node.

Our evaluation board is mounted with a 1:1 ADT1-1WT transformer from Minicircuits. You

might also use a higher impedance ratio (1:2 or 1:4) to reduce the driving requirement on

the analog signal source.

AC coupled differential input:

Figure 22 represents the biasing of a differential input signal in AC-coupled differential input

that can be forced through INCM or supplied externally (in this case, INCM may be left

internal).

Figure 22.

AC-coupled differential input

RHF1401

VIN

VINB

INCM

50

Ω

100pF

330pF

4.7µF

10nF

Analog source

1:1

ADT1-1

50

Ω

10nF

RHF1401

VIN

VINB

INCM

33pF

100k

Ω

100k

Ω

50

Ω

10nF

common

mode