THS7001, THS7002

70-MHz PROGRAMMABLE-GAIN AMPLIFIERS

SLOS214B – OCTOBER 1998 – REVISED AUGUST 1999

3

POST OFFICE BOX 655303

block diagram

_

+

PREAMP VCC+

PREAMP A IN+

PREAMP A IN–

SHDN–A

Preamp

PREAMP

OUT A

PGA–A

IN–

G2A

G1A

G0A

PGA–A REF

PGA

VCC+

PGA–B

GND

PGA

VCC–

CLAMP+ (VH)

CLAMP– (VL)

PGA–A OUT

_

+

_

PREAMP VCC–

PREAMP B IN–

PREAMP B IN+

SHDN–B

Preamp

PREAMP

OUT B

PGA–B REF

PGA–B OUT

+

G2B

G1B

G0B

PGA–A

GND

_

+

PGA–B

IN–

Figure 2. THS7002 Dual Channel PGA

input preamp

To achieve the minimum input equivalent noise required for very small input signals, the input preamp is

configured as a classic voltage feedback amplifier with a minimum gain of 2 or –1. The output of the preamp

is accessible, allowing for adjustment of gain using external resistors and for external filtering between the

preamp and the PGA.

programmable gain amplifier (PGA)

The PGA is an inverting, programmable gain amplifier. The gain is digitally programmable using three control

bits (TTL-compatible terminals) that are encoded to provide eight distinct levels of gain/attenuation. Nominal

gain/attenuation is shown in Table 1.

Table 1. Nominal Gain/Attenuation

G2

G1

G0

PGA GAIN

(dB)

PGA GAIN

(V/V)

0

0

0

–22

0.08

0

0

1

–16

0.16

0

1

0

–10

0.32

0

1

1

–4

0.63

1

0

0

2

1.26

1

0

1

8

2.52

1

1

0

14

5.01

1

1

1

20

10.0