TSA1204

Application information

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8.3

Driving the differential analog inputs

The TSA1204 is designed to deliver optimum performance when driven on differential

inputs. An RF transformer is an efficient way of achieving this high performance.

Figure 25 describes the schematics. The input signal is fed to the primary of the transformer,

while the secondary drives both ADC inputs. The 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. It determines the DC component

of the analog signal. Being a high impedance input, it acts as an I/O and can be externally

driven to adjust this DC component. 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.

Figure 25.

Differential input configuration with transformer

Figure 26.

AC-coupled differential input

Figure 26 represents the biasing of a differential input signal in AC-coupled differential input

can be let internal or fixed externally.

TSA1204

VIN

VINB

INCM

50

Ω

33pF

330pF

470nF

10nF

Analog source

1:1

ADT1-1

channels

I or Q

50

Ω

10nF

TSA1204

VIN

VINB

INCM

33pF

100k

Ω

100k

Ω

50

Ω

10nF

common

mode